TERRAIN INTELLIGENCE Ifope~}M' Oy QUARTERMASTER SCHOOL Lubflar

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DEPARTMENT OF 'THE ARMY FIELD MANUAL

TERRAIN INTELLIGENCE IfOPE~}m' Oy QUARTERMASTER SCHOOL LUBflAR. U.S. ARMY QUA. TZ. MSIR SCL, FORT LEE, VA. 22YOlS

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HEAD QU ARTER S, DEPARTMENT OF T HE ARMY OCTOBER 1967 *FM 30-10

FIELD MANUAL HEADQUARTERS DEPARTMENT OF THE ARMY No. 30-10 I WASHINGTON, D.C., 24 October 1967 TERRAIN INTELLIGENCE

CHAPTER 1. INTRODUCTION ...... -- 1-3 2. CONCEPTS AND RESPONSIBILITIES Section I. Nature of terrain intelligence _____.______.__. 4-7 II. Responsibilities -. ------8-11 CHAPTER 3. PRODUCTION OF TERRAIN INTELLIGENCE Section I. Intelligence cycle __ …...__…____-----__-- 12-16 II. Sources and agencies …...... --- 17-23 CHAPTER 4. WEATHER AND CLIMATE Section I. Weather ...... 24-39 II. Climate -...... 40-47 III. Operations in extreme climates _...... 48-50 CHAPTER 5. NATURAL TERRAIN FEATURES Section I. Significance ...... 51, 52 II. Landforms ______------53-61 Drainage...... 62-69 IV. Nearshore oceanography ...... 70-75 V. Surface materials ...... 76-81 VI. Vegetation ...... 82-91 CHAPTER 6. MANMADE TERRAIN FEATURES Section I. Significance -...... 92, 93 II. Lines of communication …...... 94-103 III. Petroleum and natural gas ____. _.______.___ 104-108 IV. Mines, quarries, and pits …...... 109-112 V. Airfields ------113-115 VI. Water terminals ______…------116-118 VII. Hydraulic structures -...... 119-121 VIII. Urban areas and buildings ...... 122-128 IX. Nonurban areas ___ _------129-131 CHAPTER 7. MILITARY ASPECTS OF THE TERRAIN Section I. Military use of terrain _.....______._____._ 132-139 Ii. Special operations ...... 140, 141 III. Water supply ------142-147 CHAPTER 8. TERRAIN STUDIES Section I. Basic features _…------…------148-153 II. Terrain and climate _-___.._____._____..__ 154-156 III. Military aspects _____- _------157-166 IV. Coastal hydrography ...... 167, 168 CHAPTER 9. TRAFFICABILITY -...... 169-178 APPENDIX A. REFERENCES ------B. OUTLINE FOR TERRAIN STUDIES ______C. SAMPLE TERRAIN STUDY ...... D. SAMPLE CLIMATIC STUDY ______.______E. NATURAL TERRAIN FEATURES ------F. DEPARTMENT OF DEFENSE INTELLIGENCE INFORMATION REPORT FORMS 1396 AND 1396C ...... INDEX ......

*This manual supersedes FM 30-I10, 28 October 1959.

CHAPTER 1 INTRODUCTION

1. Purpose and Scope 2. Changes and Comments a. This manual serves as a guide in the pro- Users of this manual are encouraged to sub- duction and use of terrain intelligence. It mit recommended changes or comments to im- shows how terrain and weather are evaluated prove it. Comments should be keyed to the in military planning and how terrain influ- specific page, paragraph, and line of the text ences combat. The manual also serves as a in which the change is recommended. Reasons guide in understanding the purpose, scope, should be provided for each comment to insure limitations, and applications of terrain analy- understanding and complete evaluation. Com- sis. The manual provides information con- ments should be forwarded to the Comman- cerning the acquisition and use of terrain in- dant, U.S. Army Engineer School, Fort Belvoir, telligence at unit level in a theater of opera- Va., 22060. tions. 3. Relation to Other Manuals b. This manual covers basic characteristics of the natural and manmade features of an The material presented in this manual is area and their effect on military operations. related to material in FM 5-30, FM 30-5, and It defines terrain intelligence and explains the TM 5-545. Other manuals of the FM 30- series intelligence process of collection, evaluation, cover specialized intelligence activities. FM interpretation of information, and dissemina- 100-5, FM 100-15, and FM 101-5 cover intel- tion of the finished intelligence. It discusses ligence in general staff activities and in the some of the sources of terrain information, plans and operations of large units. Field man- including their relative value and use. Guid- uals of the 5-series contain detailed informa- ance is furnished for the preparation of the tion on the operation of engineer troop units terrain study. The material presented herein and their intelligence functions. is applicable to both nuclear and nonnuclear warfare.

3 CHAPTER 2

CONCEPTS AND RESPONSIBILITIES

Section I. NATURE OF TERRAIN INTELLIGENCE

4. Definitions rain intelligence, he will be able to exploit the a. Terrain is part of the surface of the advantages of the terrain and avoid or mini- earth, including natural and manmade fea- mize its unfavorable aspects. By the proper tures. Both its natural and manmade features utilization of terrain, a numerically inferior affect military operations. force may achieve combat superiority over a larger enemy force. The compilation of terrain b. Terrain intelligence is processed infor- intelligence is not limited to enemy areas. It mation on the military significance of the also covers the area natural and manmade characteristics of an occupied by the friendly area. force and also the adjacent terrain. c. Terrain analysis is the process of inter- 6. Classifications preting a geographical area to determine the a. Mission. Terrain intelligence is classified effect of the natural and manmade features on according to the mission and level of the com- military operations. It includes the influence mand at which it is used. These categories are of weather and climate on those features. considered broadly as strategic and tactical or d. A terrain study is an analysis and inter- operational. Terrain intelligence is one element pretation of natural and manmade features in the intelligence requirements of a com- of an area, their effects on military operations, mander. Engineers have considerable interest and the effects of weather and climate on these in terrain because they are trained and equip- features. ped to make terrain studies and to conduct e. A terrain estimate is that portion of an field reconnaissance. analysis of the area of operations concerned b. Strategic. Strategic terrain intelligence with the military aspects of the terrain, and is concerned with large-scale plans and may in- the effects of the characteristics of terrain on clude the military capabilities of nations. Stra- enemy and friendly courses of action, including tegic intelligence is produced continuously and the possible use of nuclear weapons. requires the compilation and interpretation of information by highly specialized personnel. 5. Purpose Included in strategic intelligence are descrip- The purpose of terrain intelligence is to ob- tions and analyses of beaches, water terminals, tain data about the terrain, weather, and cli- inland waterways, urban areas, and major ter- mate, thereby assisting the commander in rain features; transportation and communica- making decisions and the troops in attaining tion systems; soils, rock types, underground their missions. In planning an operation, the installations, climate and weather, vegetation, commander and his staff analyze the effects state of ground, and hydrography. that the terrain and weather conditions will c. Operational. Operational terrain intelli- have upon the activities of both friendly and gence is produced for use in planning and con- enemy forces. The commander must make the ducting tactical or other operations. It is based most effective use of the terrain assigned to upon information secured locally or provided his unit. If he is furnished with adequate ter- by higher headquarters and is concerned pri-

4 marily with the effects of weather and ter- plans, particularly those prepared for special rain upon the particular operations of the unit. operations or for operations under extremes of Route reconnaissance reports are of greatest climate. Special studies, prepared from a logis- importance in providing current information tical viewpoint, are essential in planning op- about routes of communication. erations in mountains, jungles, or deserts, in d. Objectives. The difference in the type of snow and extreme cold, and for airborne and terrain intelligence required by strategic and amphibious operations. tactical planners reflects their objectives. The b. Problems. Research and development strategic planner may consider an entire coun- agencies are concerned with the problems re- try or continent, while the tactical planner is sulting from adverse climate, weather, and concerned only with the terrain in the area terrain. Terrain intelligence is necessary to of his operations. Where the strategic planner determine the requirements for new means of often studies problems that may arise some transportation, types of shelter and construc- years ahead and applies terrain intelligence in tion, weapons, and clothing. It is a basic re- a wide variety of hypothetical situations, the quirement in the development of new equip- tactical planner is primarily engaged with ment and in the maintenance and modification problems that currently involve his unit, al- of existing equipment. though he will study the terrain in his entire area of possible operation. c. Needs. Current and accurate terrain intelligence is required by topographic engineer 7. Applications agencies for use in preparing or revising mili- a. Planning. Terrain intelligence is essential tary maps. Civil Affairs operations depend on to the commander in order to plan strategic accurate terrain intelligence, particularly con- and tactical operations. Detailed and reliable cerning matters of economic and political im- terrain intelligence is required for all logistical pact on tactics and logistics.

Section II. RESPONSIBILITIES

8. Department of Defense functions is subject to review, ap- a. Defense Intelligence Agency (DIA). The proval, and promulgation by the Defense Intelligence Agency (DIA) is an Secretary of Defense. agency of the Department of Defense (DOD) (3) Obtaining the maximum economy and under the direction, authority, and con- and efficiency in the allocation and trol of the Secretary of Defense. It is admin- management of DOD intelligence re- istered by a director, a deputy director and a sources. This includes analysis of chief of staff at the headquarters which has those DOD intelligence activities and such subordinate units, facilities, and activi- facilities which can be fully inte- ties as are specifically assigned to the Agency grated or collocated with non-DOD by the Secretary of Defense or by the Joint intelligence organizations. Chiefs of Staff acting under the authority and (4) Responding directly to priority re- direction of the Secretary of Defense. DIA is quests levied upon the DIA by the responsible for- United States Intelligence Board (1) The organization, direction, manage- (USIB) and satisfying the intelli- ment, and control of all DOD intelligence requirements of the major gence resources assigned to or in- components of the DOD. cluded within DIA. b. Assistant Chief of Staff for Intelligence (2) Review and coordination of those (ACSI). The Under Secretary of the Army is DOD intelligence functions retained the DA's responsible officer for its intelligence, by or assigned to the military de- counterintelligence, and communications se- partments. Overall guidance for the curity in international affairs. The intelligence conduct and management of such and counterintelligence activities of the United 5 States Army are the responsibility of the As- assigned to a unit formed for that sole func- sistant Chief of Staff for Intelligence (ACSI). tion. At field army and lower levels, combat His duties include directing the Army mapping terrain intelligence is the principal concern, and geodesy program and the military geo- becoming increasingly detailed and localized at graphic intelligence program. He also has the successively subordinate levels. responsibility for coordinating those activities with Army components of unified and speci- 10. Intelligence Officer fied commands. The terrain intelligence that a commander needs to make a sound decision and an effective c. Chief of Engineers. Under the program plan must be provided by the unit intelligence direction of the Assistant Chief of Staff for officer. As a part of his intelligence report, the Intelligence, the Chief of Engineers is re- intelligence officer makes an analysis of the sponsible for- area of operations normally based upon a ter- (1) Providing direct support to the As- rain study. The intelligence officer must plan sistant Chief of Staff for Intelligence and coordinate the collection of terrain infor- in mapping and geodesy activities. mation and the production, maintenance, and (2) Providing technical supervision and dissemination of terrain intelligence. Concur- coordination of worldwide geographic rently, he should keep the officer responsible intelligence activities. for the preparation of terrain studies informed (3) Providing and directing assigned ele- of the planning that is in progress or in pros- ments engaged in mapping, geodesy, pect, so that the required terrain information military intelligence, and related serv- may be secured and compiled. ices, to include maintenance of the Department of Defense (DOD) mas- 11. Engineer ter worldwide mapping and geodesy Under the general staff supervision of G2 library and the DOD World Geodetic the staff engineer, or the senior engineer com- System. mander in the event a staff engineer is not authorized, carries out the terrain intelligence 9. Command functions. He produces and maintains terrain Commanders at all levels are responsible for studies based upon terrain analyses. This in- the production of intelligence, including ter- volves- rain intelligence. A commander must insure a. Determining the requirements for terrain that he and his staff are aware of the effects information, based upon requests from G2. of weather and terrain on their mission. He must know and utilize the capabilities for pro- b. Collecting and evaluating terrain infor- ducing terrain intelligence that exist within mation. his command or in outside agencies and insure c. Assembling terrain intelligence into a that his command gathers pertinent informa- terrain study. He provides technical interpre- tion on the weather and terrain, and transmits tation of the terrain covering such factors of this to all units requiring it. To do this prop- military significance as obstacles, routes, and erly, his command must be trained in the basic avenues of approach, cover and concealment, skills of terrain analysis. At theater level ter- landforms, hydrology, crosscountry movement, rain intelligence is more detailed than the in- and related subjects. He also disseminates ter- telligence compiled at national level, and the rain studies and technically evaluated infor- production of theater intelligence may be mation.

6 CHAPTER 3

PRODUCTION OF TERRAIN INTELLIGENCE

Section I. INTELLIGENCE CYCLE 12. Phases employed and issuance of the neces- The intelligence cycle described in FM 30-5 sary orders and requests. is also followed in the production of terrain (5) Followup. intelligence. The activities associated with in- 14. Collecting telligence operations follow a four-step cycle, Collecting is the oriented on the commander's mission. The four systematic exploitation of steps are- sources of information and the reporting of the information thus obtained to the proper a. Planning the collection effort and pre- intelligence agencies. A source is the person, paring orders. thing, or activity from which information is b. Collecting the information. obtained. An agency is any individual or orga- c. Processing the collected information. nization which collects or processes informa- d. Disseminating and using the resulting in- tion. Sources of terrain information and collec- telligence. tion agencies are discussed in paragraphs 17 through 23. 13. The Collection Effort a. Direction. Terrain intelligence is directed 15. Processing Sequence by the responsible intelligence officer in the a. Processing is the step in the intelligence name of the commander. This direction in- cycle whereby information becomes intelli- volves- gence. (1) Determination of intelligence require- b. Recording involves the reduction of in- ments. formation to writing or other graphical form (2) Preparation of a collection plan. of presentation and the grouping of related (3) Issuance of orders and requests to ap- items to facilitate study and comparison. propriate collection agencies. c. Evaluation is the appraisal of an item of (4) Continuous check on the production information to determine its pertinence, the activities of the collection agencies. reliability of the source or agency, and the b. Steps. Five successive steps are involved accuracy of the information. in direction- d. Interpretation is the result of critical (1) Determination of the information re- judgment involving analysis, integration, and quirements. deduction. Analysis is the sifting and sorting (2) Analysis of the requirements to de- of evaluated information to isolate significant termine indications that would an- elements with respect to the mission and op- swer the questions presented. erations. Integration is the combination of the (3) Translation of these indications into elements isolated in analysis with other known orders and requests for information information to form a logical picture of enemy pertaining to specific activities, local- activities or the influence of the characteristics ities, characteristics, or conditions. of the area on the mission of the command. (4) Selection of collection agencies to be Deduction is the acquisition of a meaning from

7 the hypothesis developed, tested, and consid- photointerpretation reports, and climatic sum- ered valid. maries. The information and intelligence are instruments in detecting enemy targets and 16. Dissemination and Use developing-effective combat power. The means Terrain intelligence is disseminated to com- and methods selected for dissemination depend manders and staffs as one element of the over- upon the 'detail, pertinence, and urgency of the all intelligence report. Dissemination may be information and intelligence as well as its in- accomplished by means of briefings, confer- tended use. Consideration is given to the needs ences, messages, or such intelligence documents of the user, his resources for using the mate- as the estimate, summary, periodic report, an rial, and the capabilities of available commu- analysis of area of operations, annex, maps, nications.

Section II. SOURCES AND AGENCIES

17. Maps and Terrain Models gree of acidity, nutrients, suitabil- a. Maps. Maps are a basic source of terrain ity for certain crops, and similar in- information. They are intelligence documents, formation. Engineering soil maps not supply items. Accordingly, the intelligence indicate the qualities of soil construc- officer usually is responsible for staff super- tion or vehicle movement. Agricul- vision over military maps and survey activities. tural soil maps may be used for en- The classification of US maps by type and gineering purposes after they have scale is explained in AR 117-5. Foreign maps, been interpreted according to engi- or those copied from maps that were prepared neering nomenclature and require- by foreign agencies, often vary from US stand- ments. ards and procedures. Reliability information (2) Geologic sketch maps indicate the is indicated in the margin of US produced geology of an area. Outcrop maps topographic maps. Foreign maps may not show the bedrock that is exposed. provide this. Portions of one map sheet may Bedrock maps show the surface of be fully reliable and yet other parts of the the bedrock as it would appear if the same sheet may be based on obsolete data. The overlying soils were removed. These use of a map must be regulated by an estimate maps are useful in locating sites for of the probable changes in manmade features major structures and in finding that have occurred since the date of the latest sources of rock for construction pur- revision. All personnel must be impressed with poses when the overburden has been the importance of reporting errors, changes, described. and omissions in existing maps, so that new (3) Communication maps include those editions may incorporate the necessary correc- that show the system of lines and tions. Maps prepared for a special purpose may sequence of stations of railways, pro- not be reliable for information that is not re- vide automobile route information, lated to that purpose. A railway map, for ex- and indicate navigable waterways ample, may be quite accurate in presenting and the routes and stops of airlines. railway information, but may be unreliable These really could be considered for data shown on roads or other features. transportation maps. Special maps and overlays may be prepared (4) Relief maps show differences in eleva- for a specific military purpose or to show only tion by the use of various tints and particular characteristics of the terrain. shading patterns. A plastic relief map (1) Soil maps are prepared primarily for is a standard topographic map printed agricultural purposes to show the po- on a plastic and molded into a three- tentialities of the soil for crop pro- dimensional form with a 2:1 exag- duction. This type of map shows soils geration in the relief. Because of the of various types, indicating their de- shrinkage characteristics inherent in

8 plastic materials, there is considerable Photographs preserve information in a per- distortion of the features shown on manent form, so that it is available for later this type of map. For example, some study and comparison. Remote-sensor imagery stream lines may appear not coin- includes infrared photography and side-looking cident with valley bottoms: airborne radar. It provides imagery records (5) Pictomaps are maps on which the of terrain, vegetation, and cultural features photographic imagery of a standard that may be obscured by atmospheric, natural, photomosaic has been converted into or artificial cover. interpretable colors and symbols. Des- b. Advantages. Properly interpreted, aerial ert sands, swamps, jungle, glaciers, and ground photography and airborne infrar- and extra terrestrial topography are ed and radar imagery will furnish detailed some of the features that are ideally information concerning: portrayed on a pictomap. Shadows of (1) The identification of vegetation soils map features are emphasized on the and rocks. pictomap. They accurately delineate (2) Both surface and subsurface drainage many cultural features, and they lend characteristics. Indications of surface a three-dimensional effect to buildings drainage can be located, marked, and and vegetation. This effect symbolizes evaluated through detailed stereo and establishes relative heights of study. In some cases, subsurface these cultural features. The pictomap drainage can be predicted in general is an excellent source for terrain in- terms, such as, "well-drained" or formation. "poorly drained." (6) Other special maps show the distribution of major vegetation types and (3) Suitability of terrain for construc- show depth of depressions for use in tion of airfields, roads, and under- mountain and winter operations; wa- ground installations, based upon topo- ter supply sources and distribution graphy, drainage, soils, and engineer- systems; structure of town and city ing materials. General character- plans; conditions affecting cross- istics can be given, such as"flat plain, country movement; and similar de- predominantly fine-grained soils, well- tailed information that can be pre- drained, forest cover, deposits of sented most effectively in graphic gravel suitable for borrow." form. (4) Suitability of terrain for cross-coun- b. Terrain Models. A terrain model is a try movement and airborne and air- three-dimensional graphic representation of an mobile operations. Photographs and area showing the conformation of the ground photomaps can be used advantageous- to scale. Usually it is colored to emphasize ly in studying and rating areas as various physical features, and the vertical to their suitability for movement, scale is exaggerated to convey relief. Terrain based on the evaluation of relief, models may be made for use in strategic or slopes, drainage, soils, and vegeta- tactical planning, assault landings, airborne tion. General characteristics may be landings, and aerial target delineation. determined, such as "flat plain, grass- covered, silty soils, hedgerows, poor 18. Photographs and Remote-Sensor drainage." Imagery (5) Aerial and ground photographs, in- a. General Features. Aerial and ground terpreted by skilled personnel, can photographs provide an accurate visual record give highly detailed information of the terrain. They furnish information that about all types of manmade features, is not readily available or immediately ap- from artificial obstacles to large parent by ground reconnaissance or by visual industrial complexes. observation from the air, especially of enemy- (6) Photographs depict up-to-date terrain held areas. features. Maps depict only what the 9 mapmaker saw at the time the map- distinguished. While such manmade ping information was gathered. features as roads, railroads, bridges, c. Limitations. The amount of information and buildings can be identified, the that can be derived from interpretation of interpreter may have difficulty in photography is limited by adverse weather determining their structural details. and by densely forested terrain. Aerial photo- Colored film is frequently the most graphs may not provide detailed factual ineffective for identifying vegetation. formation concerning the engineering prop- The best' scale depends on the data erties of soil, vehicle type and trafficability needed. Vegetation can also be iden- relationships, and quantitative data for mate- tified from differences in tone on rials and other items. This type of information black and white aerial photographs. usually can be obtained only through field (2) Stereopairs, vectographs, and an- sampling and laboratory testing procedures aglyphs are particularly useful in or by comparison with information from recon- making terrain studies. A stereopair naissance reports, geological surveys, and consists of two photographs of the similar sources. It is important that informa- same terrain taken from different tion obtained from aerial and ground photo- positions. Usually they are taken graphs should be correlated with information from a position vertically above the from other sources, such as maps, personal area being photographed with about reconnaissance, and reports from intelligence 60 percent of each photo (called the agencies. overlap) common to both photographs. Examination with a stereo- d. Requirements. There should be sufficient scope gives an exaggerated third-di- aerial photograph coverage made to enable the mensional view of the terrain includ- interpreter to determine the extent of local ed in the overlap. A vectograph is a conditions and the expected variations. Usually print or transparency in which the vertical coverage is best for measurements, al- two photographs of the stereoscopic though oblique photographs are more useful pair are rendered in terms of degree for certain purposes, such as in the study of of polarization presenting a stereo- dense forest areas. Scales of 1:5,000 to 1:20,- scopic image when viewed through 000 are desirable for detailed terrain analysis. Polaroid spectacles. An anaglyph is a Photographs in this range provide good area picture combining two images of the coverage and stereoscopic perception of re- same object, recorded from different lief. They show such details as major gully points of view, as images of the right characteristics, and the outstanding terrain and left eye, one image in one color features. being superimposed upon the second (1) Photographs with scales smaller than image in a contrasting color. Viewed 1:30,000 provide excellent area cover- through a pair of light filters, the an- age in the broadest sense. Major aglyph produces a stereoscopic effect. physiographic details are easily seen (3) Controlled mosaics of an area provide and studied; relief must be great, an accurate map from which measure- however, before stereovision is prac- ments of distances can be obtained. ticable because only major relief The amount of detail useful for ter- forms are clearly differentiated at rain analysis will depend upon the these scales, and small details are lost. scale of the mosaic. Major gullies can be plotted, for example, but in some cases their char- 19. Books and Periodicals acteristics cannot be determined. As Valuable terrain information can be found a rule, landforms can be delineated in a wide variety of books and periodicals. only when there is a great contrast in These include trade journals, economic atlases, pattern. Slopes associated with land- tide tables, pilots' handbooks, tourist guides, forms at times cannot be seen or and similar publications. Unpublished syste-

10 matic records covering meteorological, hydro- operations, and airborne operations. logical, and similar scientific data prepared f. Engineer Reconnaissance Reports. Re- by government agencies, engineering firms, ports that summarize data obtained by re- private societies, and individuals also contrib- connaissance are a major source of terrain in- ute valuable terrain information. Although formation. They are of particular value in utilized chiefly for terrain studies made by providing current, detailed information about higher headquarters, material of this type, lines of communication and availability of when locally available, can be of considerable natural construction materials. value to lower echelons. 21. Captured Enemy Documents 20. Intelligence Reports Maps and other intelligence documents Strategic intelligence studies prepared by captured from the enemy often are of great Department of Defense agencies provide de- value as sources of terrain information. Usu- tailed terrain information concerning major ally, enemy-prepared military maps and ter- geographical areas. Such studies include- rain studies of enemy territory will be more up a. National Intelligence Survey (NIS). This to date and detailed than our own. The proc- is a series of documents covering the coun- essing of captured enemy documents is de- tries of the world, presenting a digest of the scribed in FM 30-15. basic intelligence required for strategic planning and for the operations of major units. 22. Interrogation Each survey describes in detail the terrain Interrogation personnel should be kept in- characteristics of a specific area or nation sup- formed of the terrain information that is reported by descriptive material, maps, charts, quired by intelligence officers. Useful infor- tables, and with reliability ratings assigned to mation about the area held by enemy forces all data. frequently can be obtained from prisoners of b. Engineer Intelligence Studies (EIS). war, deserters, liberated civilians, refugees, These are no longer published, but the EIS escapees, evadees, cooperative enemy nationals, files are still an important source. These docu- and self-surrendered and apprehended enemy ments describe in detail those natural and espionage agents. manmade features of an area that affect the 23. Collection Agencies capabilities of military forces, particularly a. Units. Collection agencies include intel- with reference to engineer operations. They ligence personnel, troop units, and special in- were produced by the Office, Chief of Engineers. formation services. FM 30-5 discusses the c. Lines of Communication (LOC). These types and capabilities of these agencies. All studies, prepared on either medium scale maps units within a command may be employed by or single, small-scale foldup sheets, contain an the intelligence officer to secure terrain infor- analysis of transportation facilities with in- mation. In addition, he may request higher formation on railroads, inland waterways, high- headquarters to use their units and facilities to ways, airfields, pipelines, ports, and beaches. secure information he requires. d. Terrain Studies. These contain area in- b. Troops. Reconnaissance missions to secure telligence depicted on medium and small scale terrain information may be assigned to combat maps with accompanying textual and graphic or combat support units. Such missions may material. They are for strategic planning, and be accomplished by units specifically organiz- describe principal terrain characteristics, ed for reconnaissance or by other units as- major aspects of land, water and air move- signed reconnaissance missions in addition to ment, and key installations. their normal activities. e. Special Reports on Military Geography. c. Aircraft. In addition to ground recon- These are designed primarily for strategic naissance, aircraft may be employed to secure planning and generally directed towards anal- information about the terrain. Although it ysis of a major aspect of military geography may be limited by adverse weather or enemy such as cross-country movement, amphibious air defense, air reconnaissance is the fastest

11 means of gathering terrain information and, natural earth sciences who prepare special ter- at times, may be the most practical means rain studies, evaluate all types of terrain in- of reconnoitering enemy territory. Informa- formation, and serve as consultants to agencies tion on objects such as trees, structures, and faced with technical problems. Terrain infor- communication lines is of great importance for mation may be provided by personnel whose airmobile and air landing operations. Army normal duties are not primarily concerned with aviation has the capability to conduct air terrain intelligence. These include military reconnaissance missions, but additional sup- intelligence personnel of the MI battalion, field port may be requested through intelligence army, and MI detachments at corps. Civil channels for reconnaissance flights to be ac- Affairs staffs acquire terrain intelligence in complished by the Air Force. considerable detail, particularly in the areas of d. Specialized Agencies. An engineer ter- agriculture, forestry and fishing, transporta- rain detachment usually is assigned to each tion, and other economic functions. Civil corps. The detachment is composed of person- Affairs area studies and surveys are sources of nel in various fields of engineering and the information and intelligence.

12 CHAPTER 4

WEATHER AND CLIMATE

Section I. WEATHER 24. Definition standard references. In most English-speaking Weather comprises the day-to-day changes countries, the Fahrenheit scale is used, with in atmospheric conditions. The physical prop- the melting point of ice designated as 32°F erties and conditions of the atmosphere that above zero and the boiling point of water as must be measured or observed to describe the 212°F above zero. Countries using the metric state of the weather are termed the weather system employ the centigrade (Celsius) scale, elements. with the freezing point of water designated as 0° C and the boiling point, 1000 C. In the 25. Air Temperature United States, surface air temperatures are a. Measuring. Air temperature is the degree indicated in degrees Fahrenheit and upper of hotness or coldness of freely circulating air air temperatures in degrees centigrade. Tem- as measured by a thermometer that is shield- peratures may be converted from one of these ed from the sun. The thermometer is cali- scales to the other by use of the following brated by using the melting point of ice and formulas: the boiling point of water at sea level as C = 5 (F - 32° ) Example: Change 770 F to C. Multiply 770 F - 320 by which A,9equals2 equals 250 C. 0 0 F = - 5 X C +32 Example: Change 250 C to F. Multiply 250 C by- - and add 320, 5 which equals 770 F. b. Recording. Temperature data may be re- specific year. corded in the following forms: (6) Mean annual range. Difference be- (1) Mean daily maximum temperature. tween the mean monthly tempera- The average of the daily maximum tures of the warmest and coldest temperatures for a month. months. (2) Mean daily minimum temperature. (7) Diurnal variation. Difference be- The average of the daily minimum tween the maximum and minimum temperatures for a month. temperatures occurring in a day. (3) Mean daily temperature. Average of (8) Normal values, or long-term mean. daily maximum and minimum tem- The average of temperature values for peratures for any specific day. the entire period of record. These (4) Mean monthly temperature. Average values usually are used to evaluate of daily mean temperatures for any the climate. specific month. (9) Extreme values. Absolute maximum (5) Mean annual temperature. Average or absolute minimum or extreme of daily mean temperatures for any values.

13 (10) Length of freezing period. Number cate low-pressure areas and those significantly of days with minimum temperature above 760 millimeters usually indicate high- below freezing. pressure areas. In general, cold air, being c. Use of Data. Monthly daily maximum and heavy and.dense, causes high barometric pres- mean daily minimum temperatures usually are sures, while hot air, which is light and thin, employed to provide a general definition of the causes low pressures. High-pressure systems type of climate, and the mean annual range usually are associated with fair, dry weather; to indicate its variability. Extreme values show low-pressure systems, with unsettled, cloudy the limits which must be anticipated in the conditions. climate being considered. Temperatures also 27. Winds are recorded at various altitudes above the a. Description. Wind is air in motion and ground level in order to provide data for esti- results from differences in atmospheric pres- mating certain types of nuclear-weapon effects. sure. A wind is described by its direction and speed. The direction of a wind is the direction 26. Atmospheric Pressure from which it is blowing. A wind coming a. Definition. Atmospheric pressure is the from the north, for example is termed a north force exerted per unit of area by the weight wind. As reported in observations, wind of the atmosphere from the level of measure- direction is determined with reference to true ment to the top of the atmosphere. At sea north and is expressed to the nearest 10 level this pressure is approximately 6.66 kilo- degrees. Thus, a direction of 090 degrees (a grams per 6.45 square centimeter or 14.7 wind from due east) would be reported as 09. pounds per square inch. Mean sea level is used Wind velocities are reported by the Air as a reference for surface weather observa- Weather Service in knots. A table of wind tions, and pressure measurements are shown speeds and their specifications is given (table on weather maps and climatic charts as if the 1) to aid in estimating speeds. Over ir- entire surface of the earth were at sea level. regular terrain, a wind does not move with a Atmospheric pressures are recorded at various steady force or direction, but as a succession altitudes to provide data for estimating nu- of gusts and lulls of variable speed and clear-weapon effects. direction. These eddy currents, caused by b. Measurement. The standard device for friction between air and terrain, are called measuring atmospheric pressure is a mercurial gusts or turbulence. Turbulence also results barometer which balances the weight of the from unequal heating of the earth's surface, atmosphere with a column of mercury. The the cooler air of adjacent areas rushing in to standard atmospheric sea-level pressure is replace the rising warm air from heated areas. equal to that exerted by a 760 millimeter Usually the turbulence produced by surface (29.29 inch) column of mercury at 320 F. and friction is intensified on a sunny afternoon. at standard gravity. For some scientific b. Systems. Local pressure and wind systems purposes, it is desirable to indicate atmospheric are created by valleys, mountains, and land pressure in units of pressure (weight per unit masses that change the weather characteristics of area) rather than in units of length(centi- of areas. Since land masses absorb and radiate meters or inches). In the metric systems, a bar heat more rapidly than water masses, the land is the unit of measure. The millibar (1/1000 is heated more than the sea during the day of a bar) is used in meteorology to designate and cools more at night. In coastal areas, the value of atmospheric pressure. The warm air over the land rises to a higher standard sea level pressure is 1013.2 millibars. altitude and then moves horizontally out to One millibar equals .0762 centimeters or 0.03 sea. To replace this warm air, the colder air inches of mercury. Most weather stations to- over the water moves on to the land, creating day observe pressure on an aneroid barometer, the so-called sea breeze. The circulation is calibrated in both millibars or inches or milli- reversed at night, so that the surface air moves meters of mercury. Barometer readings sig- from the land to the sea, resulting in a land nificantly below 760 millimeters usually indi- breeze.

14 Table 1. Weather Map Scale of Wind Velocity Descriptive itenm Knots Metersfleconds Specifications Calm -...... less than 1 0-0.2 Calm; smoke rises vertically. Light air ...... 1-3 0.3-1.5 Direction of wind shown by smoke drift but not by wind vanes. Light breeze ------4-6 1.6-3.3 Wind felt on face; leaves rustle. Gentle breeze ------7-10 3.4-5.4 Leaves and small twigs in constant motion; wind extends light flag. Moderate breeze …--- 11-16 5.5-7.9 Raises dust and loose paper; small branches are moved. Fresh breeze ------17-21 8.0-10.7 Small trees in leaf begin to sway; crested wavelets form on inland waters. Strong breeze …_----- 22-27 10.8-13.8 Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. Near gale ______28-33 13.9-17.1 Whole trees in motion; inconvenience felt when walking against wind. Gale _-___-_._._._- _ 34-40 17.2-20.7 Breaks twigs off trees; generally impedes progress. Strong gale ______. 41-47 20.8-24.4 Slight structural damage occurs (chimney pots, slates and shingles removed). Storm ------48-55 24.5-28.4 Seldom experienced inland; trees uprooted; considerable structural damage occurs. Violent storm ______. 56-63 28.5-32.6 Very rarely experienced; accompanied by widespread damage. Hurricane ______64 and over 32.7 and over

bblawpppw SDCN RM

Figure 1. Chinook or foehn effect.

15 c. Vally Wind. Heated by the daytime sun, cept where the monsoon winds pick up the air in contact with a mountain slope be- moisture by moving over warm seas before comes lighter than the surrounding air and striking an island or peninsular coastline. rises up the slope, being replaced by denser, colder air. This air movement is called a valley 28. Humidity wind because it appears to be flowing up from a.' Vapor.'Water vapor is the most important the valley. At night the air in contact with constituent of the atmosphere that determines the slope becomes colder and more dense, sink- weather phenomena. Although the oceans are ing down along the slope to create a mountain the primary source, a limited amount of water breeze that seems to flow out of the mountain. vapor also is furnished to the atmosphere Mountain breezes generally are stronger than from lakes and rivers, snow, ice fields, and valley winds, especially in the winter. vegetation. The percentage of water vapor by d. Chinook. A chinook (North America) or volume in the air may vary from practically foehn (Europe) (fig. 1) is a phenomenon zero in deserts to 4 or 5 percent in humid that occurs in winter and spring on the lee tropical areas. or downwind side of mountain ranges over b. Amount. Humidity is the term used to which there flows a steady crosswind of describe the amount of water vapor in the air. moisture-laden air. As the air rises over the The amount that the air actually contains windward side of the mountains it expands and compared with what it could hold at a given cools rapidly, producing clouds and precipita- temperature and pressure is termed the relation. As the air moves down the lee side of the tive humidity. When a specific air mass holds mountain range it compresses and warms. As all the moisture that it can at a given temper- a result, there are warm, dry winds on the lee ature, it is described as having a relative side of the mountains. humidity of 100 percent. e. Fall and Gravity. Fall and gravity winds c. Dew Point. The dew point is that temper- are caused by the descent of downslope air ature at which the air becomes saturated. The through the action of gravity. They are typ- higher the dew point, the greater amount of ical of the Greenland coast, which is essen- water vapor the air can hold. The closer the tially a high plateau sloping abruptly to the dew point temperature is to the actual temper- sea along an irregular coastline cut by many ature, the greater the likelihood of condensa- fiords. The central plateau area remains ice- tion. Condensation results when the capacity covered throughout the year, developing ex- of the atmosphere to hold water is reduced by tremely cold air masses which frequently cooling, so that the water vapor in the air is drain off through the fiords to the sea and changed to visible moisture such as fog or attain a near-hurricane speed. At sea level the clouds. winds remain relatively cold and very dry. Similar winds are the bora, which drain off 29. Clouds the southern Alps and the Balkan Plateau a. Classification. Clouds are masses of con- into the Adriatic Sea, and the mistral of the densed moisture suspended in air in the form Rhone Valley in France. of minute water droplets. They are classified f. Monsoon. A monsoon wind is any season- according to their form or appearance and by ally changing or reversing wind. It is strongest the physical processes producing them. The and steadiest on the southern and eastern Air Weather Service reports the type of clouds sides of Asia. It blows outward from high- present, the heights of the cloud bases and pressure centers overland toward the sea in cloud tops, the amount of cloudiness, and the winter and inward toward low-pressure over- direction in which the clouds are moving. Cloud land in summer. In most regions, the summer amounts are reported in terms of the fraction monsoon season is generally characterized by of the sky that is covered by clouds (fig. 2). extensive cloudiness and frequent precipita- The following terms are used: tion. The winter monsoon season is character- (1) Clear. No clouds, or less than 0.1 of ized by dry air and infrequent cloudiness ex- the sky covered.

16 0 () 20 3 4

two or no clouds one-tenth three-tenths four- tenths five-tenths

Figure 2. Cloud cover symbols.

(2) Scattered. 0.1 to 0.5 of the sky cov- are separate from each other and ered. rarely cover the entire sky. The pre- (3) Broken. 0.6 to 0.9 of the sky covered. cipitation from cumiliform clouds (4) Overcast. More than 0.9 of the sky generally is showery in nature. covered. (2) Stratiform clouds usually occur in b. Heights. Cloud heights are reported in layers that may extend from horizon meters above the ground. The heights of to horizon, without the vertical de- clouds below 1,500 meters (5,000 feet) are re- velopment of cumiliform clouds. Pre- ported to the nearest 30 meters (100 feet); cipitation from this type of cloud clouds from 1,500 to 3,000 meters (5,000 to usually is in the form of light con- 10,000 feet) are reported to the nearest 150 tinuous rain, drizzle, or snow. meters (500 feet), and clouds above 3,000 e. Groupings. Clouds may be grouped into meters (10,000 feet) to the nearest 300 meters four families (fig. 3)- (1,000 feet). A ceiling is defined as the lowest (1) High. Cirrus, cirrostratus, cirrocumu- layer of clouds that is reported as broken or lus. overcast and not classified as thin. Heights of clouds are reported in meters or feet above the (2) Middle. Altostratus, altocumulus. point of observation. (3) Low. Stratus, nimbostratus, stratocumulus. c. Direction. Cloud direction is the direction toward which the cloud bases are moving. It is (4) Vertical development. Cumulonimbus reported according to the eight points of the for an example. compass. f. High Clouds. High clouds usually occur at d. Appearance. According to their appear- heights of from 6,000 to 12,000 meters (20,- ance, clouds are either cumiliform or strati- 000 to 40,000 feet), although they may be form. Cumiliform clouds are formed by rising found at much lower altitudes in polar regions. currents in unstable air. Stratiform clouds re- They are composed of ice crystals. The charac- sult from the cooling of air in stable layers. teristics of the major cloud types in this group (1) Cumiliform clouds are dense with are as follows: vertical development. The upper sur- (1) Cirrus. This is a delicate white fibrous face of a cumiliform cloud is dome- cloud that often appears bright yel- shaped, while the base is nearly low or red from the reflection of light horizontal. Usually clouds of this type from a rising or setting sun. Cirrus

17 8,000M -

25,000 FT -

7,000 M -

20,000 FT. - 6,00 M -

.. iUS I I~:~ 5,000 M -

15,000 FT - i .~~~~~i Kj . z 7s 4,000 M - dltocumulus 'z-s 'I: I

, \ - . --I V . .- -. ~- S : -"71 I ,, - or . A-.'::

.1 : ; 1.I -1

10,000 FT- 3,000 M - altostratus 'I

2pOOM -

%000 FT.-

.·n a e~sa

1,000 M -

0- I - Figure S. Major cloud types.

18 clouds may appear as isolated tufts, square miles. Usually they are thin, featherlike plumes, or streaks with and range in thickness from a few upturned ends often referred to as hundred feet to several thousand feet. mare's tails. Because of. their thin- Frequently, stratus clouds are accom- ness, cirrus clouds do not blur the panied by fog, haze, or smoke be- outlines of the sun or moon, and usu- tween their bases and the ground. ally do not make an appreciable Visibility is very poor under stratus change in the appearance of the sky. clouds, and precipitation from them (2) Cirrostratus.These are thin, whitish usually is in the form of light snow or veils of clouds that give the sky a drizzle. milky look. Usually they can be dis- (2) Nimbostratus. Clouds of this type tinguished from cirrus clouds by the form a low, dark gray layer. Precipi- halo which light from the sun or tation usually is in the form of con- moon produces in them. tinuous rain or snow of variable (3) Cirrocumulus. Clouds of this type intensity. Because of its thickness, consist of patches of small, rounded sometimes more than 4,500 meters masses or white flakes arranged in (15,000 feet), the nimbostratus is fre- groups or lines. quently classified as a cloud of verti- g. Middle Clouds. Middle clouds usually occur cal development. at altitudes of 1,800 to 6,000 (6,000 to 20,000 (3) Stratocumulus. This type of cloud feet) meters in the lower limit of this range forms a lower layer of patches of in the colder seasons, and at altitudes near the rounded masses or rolls. The base of upper limit in the warmer seasons. The major the stratocumulus usually is higher types are- and rougher than the stratus clouds. (1) Altostratus. Clouds of this type ap- Frequently these clouds change into pear as a veil of gray or bluish fibrous the stratus type. clouds, the thinner forms resembling i. Vertical. Vertical development clouds can- the thicker forms of cirrostratus. not be classified according to height, since Altostratus clouds are associated with they extend through all the levels assigned to smooth or stable air layers, and occa- other cloud groups. The bases vary from 150 sionally they produce light rain or to 3,000 meters (500 feet to 10,000 feet) or snow. higher, while the tops may vary from 450 (2) Altocumulus. This cloud type can ap- meters (1,500 feet) to more than 12,000 meters pear as a layer or in patches, is white (40,000 feet). They all occur in relatively un- or gray in color, and the cloud ele- stable air and frequently are associated with ments appear as rounded masses or strong vertical currents and intense turbu- rolls. They occur in a variety of lence. In this category are the following: forms, and may exist at several levels at the same time. (1) Cumulus. Clouds of the cumulus type are dense, with vertical development. h. Low Clouds. Low clouds usually have The base is horizontal and uniform bases below 1,800 meters (6,000 feet) and in- in height above the earth, with a top clude the following types: that is domed or cauliflower-like in (1) Stratus. These form a low layer re- shape. Cumulus clouds appear white sembling fog, although they do not when they reflect sunlight toward the rest upon the surface. They give the observer, but when viewed from di- sky a hazy appearance. The base of rectly underneath or when they are this cloud is usually rather uniform between the observer and the sun, in height but it often occurs in the they may appear dark with bright form of ragged patches or cloud frag- edges. Over land, cumulus clouds tend ments. Layers of stratus clouds may to develop during the warming of the cover hundreds of thousands of day, dissipating at night when the 19 -45 d

20 earth's surface cools. Over water, hour. Showery precipitation is marked by cumulus clouds tend to develop at rapid changes in intensity and by starting and night as the water surface remains stopping abruptly. The intensity of precipita- warm while the air mass cools tion is determined on the basis of its rate of slightly. fall. It is described as follows: (2) Cumulonimbus. Clouds of this type (1) Very light. Scattered drops or flakes are heavy masses which extend to which do not completely wet an ex- great heights. Their upper portions posed surface, regardless of duration. resemble mountains or towers capped (2) Light. Not more than 0.25 millimeter with a fibrous texture. They develop (0.01 inch) in 6 minutes. only in unstable air. Cumulonimbus (3) Moderate. 0.26 to 0.75 millimeter clouds are distinguished from cumu- in 6 minutes. lus clouds chiefly by the veil of (0.01 to 0.03 inch) ice crystal clouds which surrounds (4) Heavy. More than 0.75 millimeter their upper portions. Thunderstorms, (0.03 inch) in 6 minutes. squalls, turbulence, and hail are char- c. Intensity. The intensity of snow and driz- acteristic of cumulonimbus clouds. zle is determined on the basis of the reductions in visibility which result, as follows: 30. Precipitation (1) Very light. Scattered drops or flakes a. Description. Precipitation (fig. 4) is visi- which do not completely wet an ex- ble moisture that falls from the atmosphere, posed surface, regardless of duration. such as rain, sleet, snow, hail, drizzle, or com- Negligible effect on visibility. binations of these. As an air mass rises, its (2) Light. Visibility 1 kilometer (5/8 ability to hold moisture decreases and clouds mile) or more. form. When the cloud droplets become too statute large to remain in suspension, rain occurs or if (3) Moderate. Visibility less than 1 kilo- the air temperature is below freezing, snow is meter (5/8 statute mile), but not less formed. Sleet is frozen rain formed by droplets than 1/2 kilometer (5/16 statute passing through a layer of below-freezing air. mile). Hail consists of rounded particles composed of (4) Heavy. Visibility less than 1/2 kilo- layers of ice falling from cumulonimbus clouds meter (5/16 statute mile). with strong updrafts. Raindrops are carried to d. Amount. The amount of precipitation is high altitudes and frozen into ice pellets. They expressed in terms of the vertical depth of then fall and are carried up again by the up- water (or melted equivalent in the case of draft until the weight of the pellet is greater snow or other solid forms) accumulated within than the force of the updraft, whereupon it a specified time on a horizontal surface. This falls to earth. Freezing rain falls from the air is expressed to the nearest 0.25 millimeter in liquid form but freezes upon contact with (0.01 inch). A depth of less than 0.13 milli- objects on the surface that are at a tempera- meters (0.005 inch) is called a trace. In the ture below the freezing point. The ice formed case of snow, both the actual depth and the on these surfaces is called glaze. Air Weather equivalent in water are required. Snow depth Service observations include information on is measured to the nearest whole inch, and less the form of precipitation and its character, in- than 1.3 centimeters (0.5 inch) is termed a tensity, and amount. trace. The water equivalent of snow is deter- b. Character.The character of precipitation mined by melting a representative sample and refers to its duration and to changes in its measuring the resulting depth of water. As an intensity. It is reported as continuous, intermit- average figure, 25 centimeters (10 inches) of tent, or showery. Continuous precipitation is snow are considered to be equivalent to 2.5 that in which the intensity increases or de- centimeters (1 inch) of water, although this is creases gradually. Intermittent precipitation is subject to wide variation. The depth of snow characterized by a gradual change in intensity, is of concern in estimating the trafficability but ceases and recommences at least once an and the water equivalent is significant for 21 problems involving water supply, flood predic- pools of air which range in size from about 30 tion, stream flow, and drainage. meters to .8 kilometer (100 feet to one-half mile) in diameter. A tornado appears as a ro- 31. Fog tating funnel-shaped cloud extending toward Fog is defined as a mass of minute water the ground from the base of a cumulonimbus. droplets suspended in the atmosphere at the The low pressure and the high wind speeds surface of the earth that reduces horizontal encountered in the center of the tornado are visibility. It is formed by the condensation of very destructive. The paths of tornadoes over water vapor in the air. The most favorable the ground usually are only a few miles long conditions for the formation of fog are an and the tornadoes move at speeds of 40 to 90 abundance of water vapor, high relative hu- kilometers (25 to 55 miles) per hour. Although midity, and a light surface wind. A light wind the maximum wind speeds associated with tor- tends to thicken fog. Increasing wind speeds nadoes never have been measured directly, will usually cause fog to lift or to dissipate. property damage and other effects indicate Fog usually is more prevalent in coastal areas that they may exceed 800 kilometers (500 than inland because there is more water vapor miles) per hour. When they occur over water, in the atmosphere. Inland fogs may be very tornadoes are termed waterspouts. persistent in industrial regions. In most areas c. Tropical Cyclones. A tropical cyclone is a of the world, fog occurs more frequently dur- low-pressure system of cyclonic winds that ing the colder seasons of the year than it does forms over tropical water areas (fig. 5). Cy- in the warmer seasons. clones of great intensity are called hurricanes Storms in the Atlantic and Eastern Pacific Oceans, 32. typhoons in the Western Pacific Ocean, cy- a. Thunderstorms. A thunderstorm is a local clones in the Indian Ocean, and willi willi in storm accompanied by thunder, strong gusts Australia. The average life span of a tropical of wind, heavy rain, and sometimes hail, usu- cyclone is 6 days, although some last only a ally lasting for no more than an hour or two. few hours and others as long as 2 weeks. Tropi- A thunderstorm is cellular, each of its many cal cyclones of hurricane intensity are charac- cells having violent up and down drafts in terized by extremely strong and gusty surface close proximity. The overall mass has a charac- winds, with speeds of 117 to more than 240 teristic frontal zone with violent cool winds kilometers (73 to more than 150 miles) per racing inward toward the storm in spite of its hour; continuous intense rain in the central forward motion. When a thunderstorm reaches area, and a relatively calm area near the center its mature stage and the rain begins, a down- known as the eye. These storms vary in size draft starts in the lower and middle levels of from 80 to 800 kilometers (50 to 500 miles) in the storm. This large body of descending air diameter. The precipitation associated with causes strong, gusty surface winds that move tropical cyclones is extremely heavy. They are out ahead of the main storm area, often re- frequently accompanied by violent thunder- sulting in a radical, abrupt change in wind storms, with the heaviest rainfall usually oc- speed and direction termed the first gust. In curring some distance ahead of the eye of the general, the strongest thunderstorm winds oc- moving cyclone. Abnormally high tides are a cur on the forward side of the storm where the common companion of hurricanes and are re- downdraft first reaches the surface. These sponsible for a great amount of damage. winds ascend upward at various rates, depending on the intensity and size of the storm. The 33. Weather Forecasts actual storm has layers conducive to icing and a. Factors. A weather forecast is a predic- hail formation depending on the altitudes ob- tion of the weather conditions expected to oc- tained by updrafts and so on. The speed of a cur at a place, within an area or along a route thunderstorm wind may reach 80 to 120 kilo- at a specified future time. The accuracy and meters (50 to 75 miles) per hour for a short reliability of weather forecasts depend upon a time. number of factors, including the climatic char- b. Tornadoes. Tornadoes are circular whirl- acteristics of the forecast area, the amount 22 Figure 5. Tropical cyclones. of weather data available, the reliability of a period of 3 to 5 days, and extended-period weather communications facilities, the length forecasts cover periods in excess of 5 days. of the forecast period, and the experience of They are less detailed and specific than short- the forecaster. Other factors being equal, the period forecasts. Usually the weather informa- reliability of forecasts generally decreases as tion is expressed in terms of departure from the length of the forecast period increases. normal conditions and is suitable only for pre- b. Format. Weather forecasts may be preliminary planning purposes. sented in coded (numerical), graphical (pic- f. Severe Weather Forecasts. These provide torial), or written (plain language) format. warnings of weather conditions that will cre- Normally, weather forecasts for use by Army ate unusual difficulties. Examples of severe units will be issued in plain language form. Be- weather include tropical cyclones, thunder- cause forecasts are subject to sudden change, storms, strong and gusty surface winds, heavy they are usually transmitted by electrical precipitation, and extremes of temperature. means. Abbreviations are used extensively. The Air Weather Service furnishes such warn- The abbreviations used in weather messages ings when requested by commanders, based are contained in AR 320-50 and in the Federal upon the needs of their particular unit or in- Aviation Agency (FAA) publication, Contrac- stallation. The weather conditions that will be tions. critical vary with the type of unit or installa- c. Sources. Weather forecasts and special tion. For example, one unit may require warn- studies are provided by agencies of the Air ings of winds in excess of 15 to 20 knots, but Weather Service of the Air Force. Air Weather another may not be adversely affected by wind Service is found on all Air Force bases and on until the speed reaches 35 to 40 knots or more. many Army bases that have Army aviation 34. Weather Intelligence units. Division and lower units receive weather forecasts from either attached personnel of a. Dissemination. Timeliness is the critical Air Weather Service or from higher head- factor in disseminating weather reports and forecasts. Normally they are transmitted by quarters. radio or teletype. Weather information is in- d. Short-Period Forecasts. These forecasts corporated in such documents as the intelli- cover a period up to 48 hours in advance of gence estimate, periodic intelligence report, issue, giving detailed values of the weather ele- analysis of area of operations, and the intelli- ments expected to occur during the period and gence summary. the time of anticipated weather changes. They b. Responsibility of Intelligence Officer. The are sufficiently reliable for use in detailed intelligence officer at corps and lower levels is short-range planning. responsible for determining the weather infor- e. Medium-PeriodForecasts. This class covers mation requirements and submitting them to

23 the Air Weather Service personnel. He informs 3 hours. Chemical Corps smoke battalions can subordinate units of the weather data required furnish information concerning surface winds by the Air Weather Service and instructs them and temperature. The pilots of Army aircraft in the procedure for collecting and forwarding are capable of reporting weather conditions the data. He disseminates the received weather within their area of flight operations. Forward information and coordinates with G3/S3 in the combat units can provide weather data ob- weather training of subordinate units. tained by visual observation, and if required, c. Requirements. Weather requirements are they may be equipped with instruments for of two types-those established by the Army obtaining additional weather data. and passed to the Air Weather Service for ac- f. Interpretation.An intelligence officer does tion, and those established by the Air Weather not merely disseminate verbatim the weather Service and passed to the Army for action. The forecast received from higher headquarters. He intelligence officer coordinates all activities must interpret it in relation to particular op- directed toward satisfying these requirements. erations, He also receives interpretations from At division and higher levels this coordination such special staff officers as the chemical officer is effected through the Air Force Staff Weather (toxic chemical interpretations and interpreta- Officer, a special staff officer at those echelons. tions relative to fallout predictions and travel Below division, the intelligence officer requests of fallout clouds), the aviation officer, and the Air Weather Service support through intelli- Staff Weather Officer. The weather informa- gence channels. Army weather requirements tion that he transmits to the command must be may include climatic information to be used in presented in its most usable form, with the the planning phase of an entire campaign or operational aspects of the data indicated operation, weather forecasts, reports of cur- whenever applicable. rent weather, and weather summaries. Under conditions of nuclear warfare, timely and ac- 35. Effects of Temperature curate weather data, particularly that concern- a. Temperature. Periods of freezing tem- ing upper air wind speeds and direction, is peratures will increase the trafficability of essential in fallout predictions. Fallout pre- some soils, while with others it may create ice dictions are required both for friendly and sheets on roads, making movement more diffi- enemy employment of nuclear weapons. cult. Thawing temperatures may make frozen d. Requests. Requests for specific weather soils difficult to traverse and may damage information received by the intelligence officer roads with poor foundations. The ability of are evaluated to determine whether or not the projectiles to penetrate the earth is decreased information can be secured by organic agen- by frozen soil, but freezing increases the cas- cies before they are forwarded to the Air ualty effect of contact-fuzed shells. Melting Weather Service. In all cases, before forward- snows may cause floods and in mountain areas ing the request the intelligence officer insures result in avalanches. that requests from various units do not overlap b. Inversions. Temperature inversions create and that they cannot be fulfilled from informa- an exception to the normal decrease in tem- tion already available. perature that occurs with increases in altitude. e. Information Sources. Weather data re- In a temperature inversion, the air nearest the quired by the Air Weather Service from Army ground is colder than the overlying air. The units may be secured by artillery meteorolog- lower air remains stable. Dust and smoke re- ical sections, Chemical Corps units, Army avi- main near the ground, reducing visibility and ation, and forward combat troops. Artillery air purity. Inversion conditions are favorable meteorological sections are capable of making to either enemy or friendly employment of winds-aloft observations and of determining toxic chemical or biological agents. Radar upper air pressure, temperature, and humidity. beams may also be refracted or ducted due to In addition. they measure and,report data for inversions. fallout prediction and use by the Air Weather c. Site Selection. In selecting sites to provide Service. This information is transmitted every protection against low temperatures in the

24 northern hemisphere, preference should be The speed and direction of the wind are prime given to the southwesterly slopes of hills and considerations in areas contaminated by toxic mountains, where the temperature usually is chemical agents, biological agents, and radio- higher than on other slopes. Cold air flows logical fallout. Winds of 5 to 16 kilometers (3 downslope and remains pocketed in inclosed to 10 miles) per hour provide the most favor- drainage areas or is dammed by forests or able conditions for the employment of contam- other barriers. These cold air pockets have the inating agents. Winds below or above that lowest temperature of the terrain, and often range cause a loss of effectiveness in the use are characterized by freezing or fog when ad- of gas, smoke, chemicals, radioactive clouds, jacent areas are frost-free or clear. In areas of and mists. The direction of the wind must be frequent calm or near calm conditions such considered for the protection of friendly troops. cold air drainage areas should not be selected In areas characterized by great turbulence and for troop bivouacs or for such facilities as variable winds the use of contaminating motor pools and hospitals. In hot climates, cau- agents is highly dangerous. tion is required in utilizing cold air pockets, b. Projectiles. Winds tend to deflect projec- since they are likely areas for the formation tiles from their normal paths, particularly of ground fog and excessive humidity. In windy when they are fired at long ranges. The effect areas, on the other hand, these pockets provide that wind will have on a projectile increases shelter from the chilling effects of the wind. with an increase in the velocity of the wind Areas susceptible to cold air drainage can be and the size of the projectile. To obtain ac- readily located by ground reconnaissance or curacy in artillery fires, the direction and from topographic maps by visualizing the flow velocity of the wind must be known in order of cold and dense air over the terrain. In gen- to apply compensating corrections to firing eral, concave land surfaces facilitate the accu- data. Winds also affect the efficiency of sound- mulation of cold air, and convex surfaces favor ranging equipment. drainage of air from the surface. Toxic chem- c. Parachute Landings. Parachute landings ical and biological aerosols also tend to collect are feasible in winds up to 25 kilometers (15 in depressions and low places. In areas where miles) per hour. At higher velocities, the wind heating is required, careful selection of the tends to scatter troop concentrations, to foul terrain in locating bivouacs and other instal- equipment, and increase the number of casual- lations will save fuel. If temperature data are ties from landing accidents. Strong winds also available for various possible sites, or can be increase the time that parachutists must re- estimated by altitude factors and terrain con- main in the air, as well as the time required to figuration, fuel requirements may be closely secure equipment and prepare for combat after ascertained. Toxic chemical agents vaporize landing. more rapidly in high ambient temperatures than in low ambient temperatures. The effects d. Amphibious. Strong winds hinder amphib- of weather on toxic chemical and biological ious operations by creating high seas which agents, and on radiological contamination, are will prevent landing craft from landing or re- discussed in FM 3-5 and TM 3-240. Temper- tracting. ature has no significant effects upon the in- e. Nuclear. Wind speed and direction have tensity of blast or the thermal radiation of no influence upon the blast or thermal radia- nuclear weapons. tion effects of nuclear weapons, nor upon the range of the initial nuclear radiation. Winds 36. Winds at all atmospheric levels are significant factors, a. Description. In arid or semiarid areas, however, in determining the location of radio- strong winds frequently raise large clouds of logical fallout resulting from the surface, sub- dust and sand which greatly reduce observa- surface or airburst of a nuclear weapon. Con- tion. Similar effects result in snow-covered taminated dirt and debris carried upon the regions, where blowing snow may reduce visi- column and cloud will be deposited downwind. bility over wide areas. Observation aircraft f. Aerosols. The effectiveness of toxic chem- may be grounded entirely during such periods. ical and biological agent aerosols is influenced 25 by the direction and speed of the wind. Such connaissance. Dense clouds above the camera aerosols are dissipated rapidly in high winds. level may reduce light intensity to the point The use of toxic chemical agents in vapor form that photography becomes difficult or impossi- is most effective on clear or partially clear ble. A high, thin layer of clouds, on the other nights when the air usually is most stable. hand, may eliminate ground shadows and thus g. Radar. Strong winds can damage radar improve the quality of aerial photographs. In antennas or even prevent use of the radar. cloudy areas, close combat air support may be prohibited or restricted to aircraft equipped 37. Effects of Humidity with suitable navigation instruments. a. Ballistics. The effects of humidity upon b. Searchlights. Low-lying clouds may be ballistics are important because of the rela- used to advantage -by reflecting searchlight tionship of humidity and density. The amount beams to illuminate the ground surface. Any of water vapor in the air affects the trajectory considerable degree of night cloudiness reduces of projectiles by the influence that it has upon the amount of moonlight that reaches the air temperature and density. Humidity also ground. If the fullest utilization of twilight has an effect upon the distance that sounds periods is desired, the extent of cloud cover travel, thus affecting sound-ranging opera- must be considered. tions. Humidity does not seriously decrease the c. Nuclear. Clouds have no influence upon effectiveness of most toxic agents and may in- the blast effect of nuclear weapons that are crease the effectiveness of some, such as blister burst below them, nor do they affect nuclear gas. The effectiveness of some biological agent radiation, but they may affect the intensity aerosols may tend to be increased by moisture of thermal radiation reaching a target. If a in the air since living organisms are affected weapon is burst above or within a continuous adversely by dry air and direct sunlight. cloud layer over the target, a large portion or b. Smoke. In the use of a screening smoke, a all of the thermal radiation may be attenuated, humidity of 90 percent will have twice the ob- with a serious loss of effect. The amount of scuring effect of a humidity of 40 percent. loss will depend upon the thickness and con- With this increase in relative humidity, only tinuity of the cloud layer and the position of one-fourth of the amount of smoke-producing the burst with respect to it. If a weapon is material need be used. burst below a continuous or nearly continuous c. Nuclear. Humidity has no influence upon cloud layer, some of the thermal energy may be the blast effect or nuclear radiation of a nu- reflected from the cloud layer downward on the clear weapon and no direct effect upon thermal target area, enhancing the total thermal effect. radiation intensities. It will affect target vulnerability to a degree, because it will determine 39. Rainfall the moisture content of clothing, structures, a. Amount. When planning extended oper- equipment, and vegetation and their suscepti- ations, the average amount of precipitation bility to ignition. This effect is pronounced, occurring in the proposed area must be con- however, only when a very high or very low sidered. An area with 50 centimeters (20 relative humidity has prevailed over a long inches) or less of rainfall in a year normally period. will not have adequate supplies of water for military purposes. Rainfall of 50 to 200 centi- 38. Cloudiness meters (20 to 80 inches) a year presents no a. Effects. Daytime cloudiness reduces the serious problems in operations, other than amount of heat received from the sun at the those that occur in rainy seasons through local- earth's surface, slowing down the drying of ized flooding and poor soil trafficability. An- roads and affecting the trafficability of soils. nual rainfall in excess of 200 centimeters (80 Extensive night cloudiness prevents the loss of inches) generally hinders normal operations heat from the earth's surface due to radiational during the seasons that the greater amount of cooling and results in higher nighttime tem- this rainfall occurs. The seasonal and daily peratures. Cloudiness chiefly affects air oper- cycle of precipitation (fig. 6) affects the sched- ations by limiting aerial observation and re- uling of military activities. Seasonal distribu- 26 Figure 6. Seasonal distribution of rainfall.

tion may be uniform throughout the year or it concealment, and may facilitate surprise at- may occur in distinct wet and dry periods. In tacks. Operation of listening and sound-rang- the monsoon areas of southeast Asia, for ex- ing posts is often limited by precipitation. ample, the rains come suddenly and with such d. Neutralization. Rain and snow normally violent downpours that some military oper- reduce the effectiveness of toxic chemical and ations must cease almost entirely, and plans biological agents. Heavy or lasting rain washes must be revised. During rainy seasons in most away these agents and may neutralize them. tropical or semitropical areas, there usually are Snow may cover liquid toxic agents so that predictable periods of maximum rainfall oc- little vapor or contamination hazard appears curring at certain times of the day which must until the snow melts. Heavy precipitation will be considered when planning construction tend to dilute the concentration of biological work or tactical activities. The maximum rate agent aerosols. of precipitation expressed in inches per day or e. Communication. Precipitation may have hour may also be critical in designing culverts an adverse effect upon communications, reduc- or other facilities for draining excess water. ing the range of field wire circuits and pro- b. Trafficability. Precipitation affects soil ducing radar "clutter" which tends to obscure trafficability and hence cross-country move- target echoes. ment. In areas of seasonal precipitation, the f. Nuclear. Precipitation has a significant cross-country movement characteristics of an influence upon the blast effect of a nuclear area may change drastically each season. Sea- weapon, but no effect upon initial nuclear radi- sonal floods may swell or flood streams, mak- ation. It affects the range of thermal intensity ing fording and bridging operations difficult to the degree that it reduces visibility. Build- or impossible. Snow and sleet hamper move- ings, equipment, debris, vegetation, and other ment on roads in winter, often making them normally flammable elements will require impassable in mountainous areas. The snow higher thermal intensities for ignition, and the that accumulates in mountains during the spread of primary or secondary fires will be winter months frequently affords a water sup- limited. Residual radiation may be affected. ply throughout the year to lower, drier re- If the radioactive particles formed in an air- gions. burst are ingested into rain-bearing clouds, c. Visibility. Precipitation usually has an the nuclear cloud (if it does not rise above the adverse effect on visibility and observation, rain-bearing clouds) will become so mixed with although rain sometimes may wash excessive the rain cloud that it will become an integral impurities from the air. Rain and snow aid part of the rain-producing system. The radio-

27 active material will be deposited with the rain surface, possibly concentrating it in other over a large area. Heavy rain over an area areas where there are watercourses, low would wash away some of the material from a ground, drainage system, or flat undrained contaminating burst, either air, surface or subareas.

Section II CLIMATE

40. Definition direction of winds, amount of precipitation, a. Elements. Climate (fig. 7) refers to the and average temperatures (figs. 8 and 9) that general variation and pattern of the primary will prevail in an area can be approximated, climatic elements which include temperature, based upon statistics compiled for previous precipitation, humidity, winds, and air pres- years. These climatic elements may be de- sure. It is a composite or generalization of the scribed by graphs or charts in terms of means, day-to-day weather at a given place or area ranges, average maximums and minimums, ex- over a long period of time. The strength and tremes, and frequencies of occurrence.

Figure 7. Major climate regions.

28 Figure 7-Continued.

Figure 8. World temperatures in January.

b. Terrain. Although the heat transmitted land and ocean areas, where the land has by the sun to the earth is the dominant factor higher summer temperatures and lower winter in weather and climate, terrain has a major temperatures than the adjacent body of water. effect upon the climate in many regions. High Local terrain influences may also be highly mountains can block the movement of air significant in military operations. The ground masses and act as climatic divides. Terrain configuration often strongly affects the pattern can also effect differences in climate between of occurrence of fog, surface winds, and other

29 Figure 9. World temperatures in July. conditions. Information about these local con- tically equal in length throughout the year. ditions frequently can be obtained only by the Night temperatures usually are a few degrees analysis of topographic maps, ground recon- lower than daytime temperatures. There are naissance, and the interrogation of inhabi- no clearly marked seasons. Relative humidity tants. is high at all times, and cloudy weather pre- c. Plants. The influence of climate on the vails. There are heavy rains on at least 4 or 5 growth of plants is a predominant factor in days each week during the rainiest months, their distribution, and the relation between with the greatest amounts during the periods soil formation and climate is so close that the when the sun is most directly overhead. The pattern displayed by a soil map will provide an rains are torrential, often accompanied by indication of the climatic conditions. thunder and lightning. Ordinarily the rain begins in the afternoon, when the heated air is 41. Tropical Rainy Climates rising most rapidly, and ends before nightfall, a. Rain Forest Climate. The tropical rain although occasionally a light rain will continue forest climate occurs in a belt generally extend- into the night. ing from 50 to 8 ° on either side of the Equator. b. Savanna Climate. The tropical savanna In some regions, such as the Amazon Basin climate occurs generally in the regions from and the Congo Basin, the air is always hot and 5° to 15° on either side of the Equator, between damp, there are frequent torrential rains of the dry climates and the tropical rain forest short duration, and the winds are feeble or regions. Instead of the dense forests typical of absent for long periods of time. This climatic the tropical rain forest climate, the savanna type is also found on windward coasts, where, regions have more open forests and large areas between latitudes of 5° and 25 °, easterly trade covered with tall grasses. Savanna regions winds blow almost constantly over hills or have high temperatures, with annual ranges mountains. The cooling of these winds as they (difference between mean temperature of the rise over the barriers produces an extremely warmest and coldest months of the year) vary- heavy rainfall. This occurs, for example, in ing between 5° and 15° F. The total amount of portions of Hawaii, the Philippines, the eastern rainfall is less than that of the tropical rain coasts of Central America, Brazil, Madagascar forest climate. There are distinct wet and dry (Malagasy), and most of the islands in the seasons, and usually the rainy season begins southern Pacific Ocean. In this type of climate, and ends with squalls and violent thunder- the rays of the sun are nearly vertical most of storms. During the rainy season, periods of the time, so that days and nights are prac- intensely hot sunshine also alternate with

30 brief, violent deluges of rain. The amount of is meager and erratic. Steppe regions on the rainfall varies considerably, so that there are poleward sides of deserts have almost all their years of drought and years of flood. In the dry annual rainfall in the cool season. Those ad- season the weather resembles that of desert joining savannas on the equatorward sides of regions, with very little rainfall. Trees lose deserts generally have a brief period of rela- their leaves, many small streams are dry, and tively heavy rains during the time when the the soil becomes hard and cracked. Visibility sun is highest. is greatly reduced by dust and the smoke from d. Middle-Latitude Dry Climates. These oc- grass fires. cur within the deep interiors of continents, in c. Monsoon. In certain parts of southern and the regions surrounded by mountains or pla- southeastern Asia, the climate is greatly in- teaus that block the humid maritime air fluenced by monsoon winds. The wet and dry masses. Rainfall is meager and undependable, seasons coincide respectively with the onshore as in the low-latitude deserts, but there is also and offshore winds. a season of severe cold. In winter there may be a small amount of snow, frequently accompa- 42. Dry Climates nied by strong winds. The temperature and a. Description. Dry climates are those in weather characteristics are similar to those which the evaporation rate exceeds the pre- of humid continental climates in comparable cipitation rate. The dry climates are located latitudes, except that there is less rainfall. The on the leeward interior portions of continents. area immediately to the east and west of the There are two subdivisions: the arid or desert Caspian Sea is a typical example of this type, and the semiarid or steppe type. In gen- climate. eral, the steppe is a transitional region sur- e. Middle-Latitude Desert Climate. This rounding the desert and separating it from the climate is characterized by lower temperatures humid regions. Dry climates are characterized and precipitation than low-latitude desert cli- by extreme seasonal temperatures with large mates. This climate occurs in the basinlike, annual ranges. Daily ranges also are high. low-altitude areas, surrounded by high-land Humidity is relatively low, averaging from 12 rims, that exist in some continental interiors. to 30 percent around the middle of the day. The Great Basin of the U.S. and the Turkestan Generally the skies are clear and cloudless. Basin of Asia have this type of climate. Sum- Because vegetation is meager, the barren sur- mer temperatures are high. Middle-latitude face of the dry earth becomes very hot during steppes occupy intermediate locations between the day and cools rapidly at night. The vegeta- deserts and humid climates. They have small tion offers little friction to the moving air, amounts of rainfall, which is usually unpre- and accordingly, strong, persistent winds are dictable in amount or time of occurrence. typical of desert regions. b. Low-Latitude Desert Climates. These oc- 43. Humid Mesothermal Climates cur in the vicinity of 20 ° to 25' north or south, a. Description. These climates are character- with the average positions of their extreme ized by moderate temperatures that occur in a margins at approximately 150 and 30°. The seasonal rhythm. They are divided into three Sahara and Australian Deserts are typical ex- general categories-Mediterranean climate, amples of this type of climate. In these desert humid subtropical climate and marine west regions, rainfall is not only small in amount, coast climate. but erratic and uncertain. However, infrequent b. Mediterranean Climate. This climate has heavy showers may turn dry streambeds into hot, dry summers and mild winters, during raging torrents. Often there is no rainfall for which most of the annual precipitation occurs. several years, and the skies are almost always Annual rainfall usually ranges from 38 to 64 clear and cloudless. centimeters (15 to 25 inches). In the winter c. Low-Latitude Steppes. These are semiarid, months, the average temperature is usually having a short period of rain-bearing winds between 40 ° and 50°F.; in the summer, it and storms each year. Precipitation, however, ranges generally from 700 to 80 ° F. This type 31 of climate occurs in five regions-the border- tropical air mass, then be reduced by a sub- lands of the Mediterranean Sea, central and sequent polar wind as much as 300 F. in 24 coastal Southern California, central Chile, the hours, resulting in a severe freeze. southern tip of South Africa, and parts of d. Marine West Coast Climate. This climate southern Australia. Coastal areas often have a occurs on the western or windward sides of modified type of Mediterranean climate, with continents, poleward from about 400 latitude, cool summers accentuated in some areas by the and results from onshore westerly winds that cool ocean currents offshore. There is apt to be blow over the land from adjoining oceans. It a cool daily breeze along the seacoast and for a borders the Mediterranean type on its equator- short distance inland. Relative humidity is ward margins, extends into the higher middle high. Fogs are frequent, but usually are dissi- latitudes and ends at the subarctic or tundra pated by the heat of the sun in the early morn- climate. Where mountains are closely parallel ing hours. Winters are mild and frost infre- to the west coast, as in Scandinavia, this type quent, and the annual change in temperature of climate is confined to a relatively narrow at some locations is uncommonly small. Sum- region on seaward side of the highlands. In mer days in Mediterranean climates are warm parts of western Europe, where there are ex- to hot, with bright sunshine, low relative tensive lowlands, the effects of the ocean con- humidity, and nearly cloudless skies. Daily ditions have an influence on the climate for weather becomes erratic and unpredictable in many miles inland. Summers are cool with oc- autumn. The winds are less regular and there casional hot days but no severe or prolonged is occasional rain. Temperatures remain rela- heat waves. Rainfall is fairly abundant. Win- tively high. Winters are mild and warm, with ters are mild, particularly in western Europe, occasional frosts and relatively abundant rain- where a great mass of warm water known as fall. the North Atlantic Drift lies offshore. Cloudy c. Humid Subtropical Climate. This climate skies and a humid atmosphere are prevalent. occurs in regions located on the eastern sides There are frequent severe frosts. The midday of continents, generally from about latitude temperatures of most winter days are rela- 25° poleward (north or south) to 350 or 400. tively high. During unusually cold periods, This type of climate is found, for example, in temperatures may remain below freezing for the American Gulf States. Temperatures are several days. The winter season is marked by similar to those of the Mediterranean climate, severe storms, fogs, and mist. Where the west- with less contrast between regions on the ern coasts are bordered by mountain ranges, as coast and those located inland. Rainfall ranges in Norway and Chile, precipitation may reach from 75 to 165 centimeters (30 to 65 inches) a total of 250 to 380 centimeters (100 to 150 a year at most locations. In the summer, hu- inches) a year. In areas consisting predomi- midity is high, temperatures average from nantly of lowlands, rainfall usually averages about 75 ° to 80°F. in the hottest month, and from 50 to 90 centimeters (20 to 35 inches) there are frequent thundershowers. Nights are a year and may fall steadily for several days hot and sultry. There is no drought season, but at a time. In mountainous regions, such as the normally there is less rain in winter than in Cascade Range or the Scandinavian Highlands, summer. Severe tropical cyclones occur most snowfall is very heavy. The marine west coast frequently in the late summer and early fall. climate is cloudy, and has mist or fog for at Winters are relatively mild in this type cli- least 40 days a year at many locations. mate. Temperatures in the cool months usually average between 40° and 55°F. with the mid- 44. Humid Microthermal Climates day temperature around 55° to 60°F. and the a. Types. The humid microthermal climate night temperature from 350 to 45°F. The high occurs in the Northern Hemisphere northward humidity, however, makes the nights chilly from the subtropical climatic regions and in and uncomfortable. Snow may fall occasion- leeward interior locations. Latitudinal spread ally, but it does not remain for more than 2 is from about 400 N to 600 or 650 N. It has or 3 days. Daytime temperatures may be colder winters than the mesothermal type, raised above 60 ° or 70°F. by the arrival of a with larger annual changes of temperature,

32 longer frost seasons and snow cover that lasts e. Subarctic Climate. This climate occurs in for considerable periods. Humid continental latitudes of 50 ° to 60 ° in the Northern Hemi- and subarctic are the principal types of micro- sphere. The Eurasian region extends from thermal climate. Finland and Sweden to the Pacific coast of b. Humid Continental Climates. These cli- Siberia, and in North America, the subarctic mates border the marine west coast climatic stretches from Alaska to Labrador and New- regions. Where there are mountain barriers, as foundland. Long, extremely cold winters and in North America, the change between the two very brief summers characterize this type of types of climate is abrupt, but it is very grad- climate. Winter quickly follows summer, with ual where there are no barriers, as in the low- only a short period of autumn intervening. A lands of western Europe. Seasonal differences large part of these regions are frozen to a con- are extreme, with very cold winters and warm siderable depth, with only a few feet of the to hot summers. Along the seaboard, the sum- upper part thawing out in the summer. There mer heat is oppressive and sultry because of is little precipitation in subarctic regions. No the higher humidity, and the winter cold is more than 40 centimeters (15 inches) a year more raw and penetrating than in the drier falls over the greater part of the Siberian area. interior regions. Along the interior margins, In most of subarctic Canada the precipitation humid continental climates border upon the is less than 50 centimeters (20 inches) an- dry climates and have subhumid character- nually. Precipitation exceeds 50 centimeters istics. The prairies of North America and in- (20 inches) chiefly along the oceanic margins terior Eurasia are examples of such climatic of Eurasia and North America. regions. In these areas, the maximum rainfall 45. Polar Climates usually occurs in late spring and early summer, a. Location. The poleward limit of forest rather than at the time of greatest heat. In winter, regions with a humid continental type growth usually is considered the dividing line between polar climates and those of intermedi- of climate normally have a permanent snow ate latitudes coinciding with a line (isotherm) cover that lasts from a few weeks to several months. Summer rains usually occur in sharp connecting points having a temperature of showers accompanied by thunder and light- 50°F. for the warmest month. A mean annual temperature of 320 F. or below is also ning. Winter in the prairie regions is charac- a dis- tinguishing feature of polar climates. In the terized by frequent changes in weather con- Southern Hemisphere, the only large land area ditions, with occasional blizzards, known as burans. A blizzard is marked by violent gales, with a polar climate is the Antarctic continent. In the Northern Hemisphere, this climatic drifting snow, and extreme cold. Although region includes the Arctic Sea, the borderlands there may be no precipitation falling, the air is filled to a height of several hundred feet by of Eurasia and North America, with the island groups that are north of these continents, and swirling masses of dry, finely pulverized snow. ice-covered Greenland. The Arctic is almost a Afternoon thunderstorms frequently occur during summer in prairie regions. landlocked sea and the Antarctic is a seagirt land with important climatic differences be- c. Southern Margins. Regions on the south- tween them. The climate has fewer wide vari- ern margins of microthermal climates have ations in the Antarctic because it is a single long, hot, and humid summers lasting from land mass surrounded by oceans with a uni- 150 to 200 days between the periods of frost. form temperature. Winters are cold, with frequent intervals of b. Temperature. Polar climates have the mild, rainy weather. lowest mean annual and summer temperatures d. Winter. Winter is the dominant season and although the sun remains above the on the poleward side of regions with this type horizon for 6 months of the year, the rays are of climate. Summers are relatively short, usual- too oblique to raise the temperature signifi- ly comprising a period of about 5 months. Tem- cantly. Much of the energy from the sun is perature changes of as much as 40° F. in 24 reflected by snow and ice, and is consumed in hours are common in spring and autumn. melting the snow cover and evaporating the

33 water. As a result neither the land surface nor 50°F., the ground is free from snow for a short the air adjacent to it becomes warm. period and low sparse vegetation is possible. c. Precipitation. Precipitation averages less This climate is designated as tundra. It is less than 25 centimeters (10 inches) a year over rigorous than that of the icecap regions. The large parts of the polar land areas. Because warmest month isotherms of 50°F. on the of the low evaporation and small amount of equatorward side and 32°F. on the poleward melting, permanent ice fields several thousand side are considered to be the boundaries. Over feet thick have accumulated on Greenland and land areas, tundra climate is confined largely the Antarctic continent. to the 'Northern Hemisphere. Ocean prevails in those Antarctic areas where the tundra cli- 46. Tundra and Icecap mate normally would be found. Summers warm a. Tundra. Polar climates usually are di- enough to develop a tundra climate occur only vided into two types-icecap and tundra. Ice- in the most northerly fringes of the Antarctic cap climates are those where the average and on certain small islands of the region. The temperature of all months is below 32 ° F., vege- most extensive tundra areas are on the Arctic tation will not grow, and a permanent snow- Sea margins of Eurasia and North America. and-ice cover prevails (figs. 10 and 11). When Long, cold winters and brief, cool summers one or more months in the warm season have characterize the tundra climate. an average temperature above 320F. but below

i- .

Figure 10. Arctic terrain.

b. Temperatures. Average temperatures usu- -35 ° to -40°F. in January and February, ally are above freezing only for from 2 to 4 with even lower temperatures inland. Along months of the year, and killing frosts may oc- the Arctic borders of North America, the tem- cur at any time. Fog is prevalent along the perature for comparable periods is higher, and coast, frequently lasting for days at a time. winters are less severe. Snow cover disappears for 1 or 2 months dur- c. Precipitation. Annual precipitation nor- ing the summer season, and the lakes usually mally does not exceed 25 cm to 30 cm (10-12 are free from ice. Drainage is poor because of inches) in the tundra regions, although larger the permafrost, resulting in many bogs and amounts are received in parts of eastern Can- swamps. Summer temperatures do not differ ada, particularly in Labrador. Usually the most greatly in the various tundra regions. There is, precipitation occurs in summer and autumn, however, a considerable variation in winter the warmest seasons. Most of it is in the form temperatures. Average temperatures in the of rain, with occasional snow. The winter snow Arctic coastal areas of Siberia average about is dry and powdery, forming a compact cover. 34 Figure 11. Arctic tundra, showing warm-weather drainage.

Often it is accompanied by strong blizzard expected during the period of the proposed op- winds which pile up the snow on the lee sides erations. These studies are of particular value of hills and in depressions, sweeping exposed in developing new equipment and in anticipat- surfaces bare. There is no vegetation to break ing logistical problems. Special climatic stud- the force of the wind and to hold the snow ies may be prepared covering winds, rainfall, cover. tides, sea conditions, state of ground, and simi- d. Icecap. This climate characterizes the lar aspects of a specified area. Such studies permanent continental ice sheets of Greenland have been made, for example, to provide data and Antarctica and the ocean in the vicinity for use in determining- of the North Pole. The average winter-month (1) Location of camps, training areas, temperatures range from -35 ° to -45°F. depots, and landing fields. Storms or violent winds do not occur as fre- (2) Coastal areas most suitable for am- quently in the inner portions of the icecaps as phibious operations. in other climatic regions, but in some marginal (3) Operations of aircraft over certain areas there are extreme gales caused by the mountainous areas. precipitous descent of cold air from the con- (4) Smoke behavior in specified localities. tinental ice plateau. (5) Seasonal fuel requirements by weight, quantity, and type. 47. Climatic Studies b. Requests. Requests for climatic studies a. Records. Climatic studies are based upon should be made as far in advance as possible, the records of past weather in a given area and should provide all pertinent information, compiled over a long period of time. They are including mission, area and time, operational used in preliminary planning to provide an limits, flexibility permitted, and the form of estimate of the climatic averages that may be presentation.

Section III. OPERATIONS IN EXTREME CLIMATES 48. Desert Regions may reach 120' to 130°F. During daylight a. Weather. High summer temperatures are hours the thermal action may be so violent normal in desert areas; the summer maximum that planes cannot operate safely at lower alti- 35 tudes. The variation between day and night the mines. In heavy dust and sandstorms, the temperatures is great, the temperature often operations of mechanized units are similar to dropping below the freezing point in winter. those conducted at night. These sudden changes in temperature occa- b. Natural Features. There are few land- sionally give rise to winds of hurricane force marks in a sandy desert region. The most that carry large quantities of dust and sand. prominent features are the huge dunes created Under these conditions, visibility is very poor by sandstorms (fig. 12). Usually the surface and movement may be impossible. Climatic of a sand dune is packed firmly by the wind conditions in desert areas also increase main- for a depth of about 5 centimeters (2 inches). tenance requirements of mechanized units. This surface will support considerable weight, Rain is infrequent in desert regions, usually but detours may be necessary because many of averaging less than 25 centimeters (10 inches) the dunes are high, with steep slopes. Areas of a year, but it may come in sudden downpours. loose sand impede movement on foot or by Water sources are few, and frequently are pol- wheeled vehicles, but tracked vehicles are able luted and brackish. Usually water for military to operate in shallow sand. In flat, hard- forces must be transported by tank truck, rail, surfaced areas, roads and trails are not neces- or pipeline from sources outside the desert sary and all types of vehicles can move cross- area. Winds blow almost constantly in the country. Salt marshes, dry lakes, and wadis desert, frequently limiting the use of smoke (dry streambeds) occur along coastal areas or and other chemical weapons. Minefields may inland in depressions. Wadis and dry lakes are be made useless by the blowing dust and sand. impassable when wet and contain a powdery The wind either blows away the sand, expos- silt when they are dry which may cause ve- ing the mines, or deposits large quantities of hicles to bog down. it on the minefield, preventing detonation of

, V :,~~~~~~-__ . 6. --_4" 4>7··;- 11 ..4 ..tI ...... rL~~i·'~ '7i M_

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Figure 12. Sand dunes (Death Valley, California). 36 c. Manmade Features. Well-defined roads in summer and are evident in a wide are scarce in desert regions, although there arc which increases as the sun be- usually are trails between water sources. Occa- comes higher in the sky. The effect of sionally flash floods may cut the routes for a mirage generally is the distortion short periods of time. Dust and sa'nd storms of objects, particularly in the vertical may prevent traffic through lack of visibility dimension. This has an adverse effect and maintenance difficulties. A surfaced main upon observation, making it partic- supply route is essential and usually must be ularly difficult to identify vehicles. constructed. Road location is difficult and time- Distances in deserts are underesti- consuming, requiring extensive map study and mated. Shadows on the light-colored area reconnaissance. Buildings must be strong terrain can be seen for miles but tend enough to withstand the frequent high winds to distort distant objects. Moonlight and constructed tightly to reduce the infiltra- in desert areas is much brighter than tion of blowing sand and dust. Field fortifica- in other regions and nights usually tions in sand require adequate strengthening, are very clear, with the haze and with a maximum use of sandbags. In rocky glare eliminated. Observation at night deserts, field works can be installed only with may be better than during some pe- great difficulty. Field fortifications are easy to riods of the day. In open terrain, dig in sandy deserts, but they must be revetted, sound- and flash-ranging are particu- and may be filled quickly with drifting sand. larly effective. Artillery observers, d. Military Aspects. however, may find few positions that (1) Key terrain features. In desert op- will allow a commanding view of the erations, terrain features usually are terrain. The ability of a weapon to not major objectives, since the posses- fire effectively in the desert usually is sion of a particular piece of ground limited only by the range of the seldom contributes materially to the weapon and the ability of the ob- destruction of the enemy force. Oases server to adjust fire. There is little and other water sources are always vegetation or relief to mask weapons. critical, however, because an adequate (3) Cover and concealment. Cover from water supply is a fundamental re- enemy fire may be afforded by sand quirement of military operations in dunes, hills, and other irregularities arid or semiarid regions. in the desert terrain. Concealment is (2) Observation and fields of fire. The hard to obtain, since the vegetation brilliant sunlight of desert areas re- is sparse. Camouflage is used more ex- flected from the light colored ground tensively in desert areas than in nor- surface creates a glare. An observer mal terrain, and reliance must be with the sun to his back may see placed upon artificial means. Camou- well, but the glare greatly reduces flage from air or ground observation visibility when he faces toward the is extremely difficult to achieve. The sun. He loses his depth perception and movement of troops during daylight will confuse objects which are in is greatly restricted due to the lack shadows or haze. On hot days, a shim- of concealment and cover from air at- mering haze may nullify ground ob- tack and troops must be widely dis- servation at ranges of 450 meters persed. (500 yards) or less, depending on (4) Obstacles. There are relatively few local conditions. An optical phenom- major obstacles to movement in most enon encountered in desert regions is desert regions. Although the road net the mirage, an effect produced by lay- is limited, cross-country movement ers of air of varying density across may be good, varying with the type of which the observer sees reflections, surface materials. usually inverted, of some distant ob- (5) Nuclear weapons. The ease of disper- ject or objects. These occur frequently sion in desert areas avoids a concen-

37 tration of troops that could provide central and west Africa, the rain forest con- a profitable target for nuclear weap- sists of several stories of trees, the foliage of ons. Suitable targets are provided, which forms a dense canopy, preventing sun- however, by airfields, communication light from reaching the forest floor, and thus centers, and supply installations. precluding dense undergrowth. In other areas, (6) Toxic chemical and biological agents. such as in Southeast Asia and some islands in Two characteristics of desert regions the Pacific Ocean, where a monsoon climate pre- which limit the employment of toxic vails, the rain forest has a canopy only partly chemical agents are the sparseness of continuous and a dense undergrowth. Rain vegetation and the extreme variations forest is commonly called "jungle," but the in ambient temperature. Toxic agents term "jungle" is not recognized as a vegetation present storage problems because of type. Terrain covered by the rain forest varies the wide temperature ranges and the from mountain ranges to low, swampy plains. extreme conditions existing during In Southeast Asia, the Pacific Islands, and parts the day. Effective use of toxic chem- of Latin America, the rain forest covers ir- ical agents usually is limited to night. regular terrain. Other rain forest areas, such The direct sunlight and dry air which as those in central Africa and South America, characterize desert regions may pre- generally are low and level. Some coastal por- sent unfavorable environmental con- tions of rain forest areas are characterized by ditions for some biological agent mangrove swamps or by open beaches lined aerosols. with bamboo or coconut groves. Beyond the (7) Screening smokes. Under desert con- shoreline there may be paddy fields or pine- ditions when the winds are still, apple, coconut, sugar cane, or rubber plana- large-area smoke screening is of con- tions. Between these and the rain forest there siderable importance because of the may be low-lying foothills covered with brush normal lack of adequate natural con- or tall grass. Streams are numerous in rain cealment and cover. forest areas, but they are generally muddy and subject to sudden floods. In wet seasons an en- 49. Tropical Regions tire area of flat rain forest may become a con- a. Weather. Excessive heat and humidity tinuous swamp. In mountainous areas streams except in tropical deserts characterize that normally are shallow become torrential t r o p i c a l regions throughout the year. shortly after a heavy rain. The characteristics In the rain forest type of climate, there is little of rain forest terrain and its effects upon mili- seasonal variation in temperature. The weather tary operations are discussed in FM 31-30. is marked by sudden changes, with torrential c. Manmade Features. There are few roads rains that end abruptly to be followed at once or trails in rain forest areas. Usually roads by bright sunshine. Humidity tends to remain must be constructed, and the use of these is high because the vegetation checks evapora- limited to light trucks or light tracked ve- tion. Although monsoon areas have a dry sea- hicles. Except for coral in some coastal areas, son, the total rainfall is so great that rain there is a lack of materials suitable for road forest vegetation is dominant. High tempera- construction. The dense vegetation, unstable tures prevail in the tropical savanna regions, soils, and poor drainage make roadbuilding which have distinct wet and dry seasons; but difficult. To establish and maintain a road net in most of these areas, grass is the predomi- of even minimum standards calls for greater nate vegetation. Both rainfall and relative engineer effort than in other types of terrain. humidity are high in the wet season, and rain- Navigable waterways often provide the most fall is rare and relative humidity ranges from efficient routes of communication, although low to high. they are highly vulnerable to ambush. Bridges b. Natural Features. Military operations in suitable for military loads rarely exist in tropical regions are influenced chiefly by the jungle regions. The construction of bridges is rain forest vegetation. In some areas, such as complicated by the frequency and intensity the Amazon Basin of South America, and in of flash floods, the tendency of some jungle 38 streams to shift their courses, and the rapid readily noticeable from the air. Be- decay of wooden structural members. Engi- cause observation is limited, tactical neers must be prepared to repair or replace units must employ narrow frontages, bridges rapidly at short notice. Aerial trams reduced distances and intervals be- are useful because of the deep cuts made by tween elements, increased patrol ac- jungle streams in hilly or mountainous ter- tivity, and a larger number of liaison rain. Towns and villages in jungle regions parties than required in more open rarely provide suitable facilities for military terrain. The difficulties of observation installations. Usually settlements are avoided greatly restrict the employment of for hygienic reasons. Excellent anchorages may supporting arms and weapons. Artil- be found along many tropical coasts, but there lery forward observer teams on the are very few water terminals sufficiently de- ground usually cannot see the burst veloped to be of any value in military opera- and must adjust fire by sound spot- tions. ting and sound sensing methods. d. Key Terrain Features. In jungle areas, Aerial forward observers may be uti- the key terrain features generally are those lized with a higher degree of reli- that provide control of trails, navigable water- ability. Data based on maps or ways, and beaches suitable for amphibious photomaps can be used only to a landings. Possession of the edges of an area limited extent. of high rain forest could provide observation (2) Fields of fire. Since natural fields of points, thus giving advantages similar to those fire generally are limited to about 5 derived from the possession of high ground. or 10 meters (5 or 10 yards), lanes e. Observation and Fields of Fire. must be cleared. Where the under- (1) Observation. In rain forest, the dense growth is heavy, several days of labor vegetation often limits observation to will be required to clear 90-meter short distances. Usually the canopy (100-yard) fire lanes around a posi- in a primary rain forest, which con- tion. In order to avoid revealing wea- sists of a virgin growth of mature pon positions, a fire lane in dense trees, is so thick that it cuts off most vegetation usually is in the form of sunlight, and visibility is limited to a tunnel from 1 to 3.5 meters (1 to about 20 or 30 meters (20 or 30 4 yards) wide, with the overhanging yards). Visibility may be limited foliage left intact. In rain forest, the about 5 meters (5 yards) or less in most effective weapons are those that the secondary forest, which is com- can be supplied easily with ammuni- posed of a second growth that de- tion and are readily transportable velops when the original forest has over difficult terrain. Suitable wea- been burned off or cut. Rain, clouds, pons include mortars, machineguns, and the steamy exhalation from wet automatic rifles, and grenades. Arm- areas also tend to reduce visibility. ored vehicles cannot move through Because of the limited visibility and rain forest unless routes have been the lack of conspicuous landmarks, it prepared. Usually the movement of is often difficult to locate a ground tanks is limited to beaches, coconut position from a map. Camouflage groves, clearings, and improved from close ground observation is of trails. The principal value of tanks is the greatest importance in the rain in the use of their flamethrowers, di- forest. In most areas, however, there rect fire weapons, and crushing is less need for artificial camouflage weight in the destruction of enemy against air observation. Whenever field fortifications. Tanks are highly possible, the natural overhead is pre- vulnerable to ambush and close in at- served, since any break in the tack in rain forest terrain. Because normally uniform tree canopy is the heavy vegetation reduces the ef- 39 fective bursting radius of artillery h. Communications. Visual signaling is sel- shells, weapons of 105-mm or higher dom effective in the rain forest because of the calibers must be employed to blast dense growth. The use of messengers is slow away jungle undergrowth and destroy and may be hazardous. Wire circuits are hard enemy positions. Artillery pieces to install and maintain. The range of radio should be capable of high-angle fire sets may be greatly reduced by the vegetation, and should be drawn by tractors or resulting in ranges from 40 to 70 percent less transported by helicopters. Engineer than those considered normal in open or light- equipment must be available for the ly wooded terrain. improvement of trails, construction of i. Toxic Chemical and Biological Agents. firing positions, and clearing of fields Both the weather and terrain conditions in of fire. In some mountainous areas, rain forest areas are favorable for the em- only pack artillery may be practica- ployment of chemical and biological agents. ble. Air forces are effective in close Where the overhead canopy is very dense, how- tactical support of ground elements, ever, sprays from aircraft usually are only but their utility for tactical bombing moderately effective against personnel. The is less than in other types of terrain. large-scale use of defoliants will increase the Armed helicopters are used extensive- fields of fire of weapons, and provide increased ly in close support of ground forces. observation. f. Cover and Concealment. Rain forest provides concealment from air and ground obser- 50. Arctic and Subartic Regions vation and may furnish some cover from small a. Weather. Severe changes in weather are arms fire. The amount of cover given by slit common in arctic and subarctic regions. These trenches and other field fortifications is often changes include shifting periods of severe limited by the high water table, which pre- frosts, mild weather, sudden freezing, snow- vents excavating more than a few feet below storms, strong winds, and dense fogs. Reliable the surface of the ground. and timely weather forecasts are essential to g. Avenues of Approach. Cross-country guard against damage to equipment and instal- movement in rain forest is slow and difficult. lations and to gain any tactical advantages Troops may have to cut their way through con- that may be possible by exploiting changes in tinuous thick undergrowth or make lengthy de- weather conditions. Arctic operations fre- tours to avoid impassable swamps. On most quently are hindered by strong winds, which usually occur trails, troops must move in more often along the coast than a column of files, in the interior. Wind speeds in excess of 128 and the average rate of movement rarely ex- kilometers (80 miles) ceeds per hour have been re- 1.5 km per hour. Usually foot movement corded at coastal stations. may Winds blow con- be made most easily on ridges, where the tinually, and in most areas there are no hills, vegetation is more open and the better drain- mountains, or other natural barriers to pro- age results in less muddy surfaces. Except for vide protection. Blowing snow constitutes a small, fast streams with traversable beds, serios hazard to flying operations. Winds of movement is poorest along the banks of rivers, 16 to 24 kilometers (10 to 15 miles) per hour because of the dense vegetation, mud, swamps, will raise the snow several feet off the ground, and tributary streams. Even in comparatively obscuring such surface objects as rocks and dry weather, mud slows down vehicular traffic runway markers. The short days and long in the jungles. It may be necessary to supple- nights of winter reduce the amount of daylight ment motorized transport by the use of heli- available for tactical operations and work ac- copters and carrying parties. Jungle roads and tivities. Nights often are bright because of the trails rapidly disappear unless they are in con- illumination of the moon, stars, aurora bore- stant use. Accordingly, maps showing these alis, and reflections from the snow, so that features seldom are reliable. Air photographs night movements are possible. The short sum- of jungle terrain rarely reveal more than the mer nights permit military operations through treetops. the 24-hour period. 40 b. Natural Features. Following a heavy bridges of temporary construction. Runways snowfall, landmarks and other objects become and landing strips will require considerable covered, making orientation difficult. Gullies maintenance. Airfields that have been improp- and ditches are filled and obscured so that erly designed and constructed may become movement is made more hazardous. The freez- wholly inoperative for extended periods. ing of swamps and lakes may convert obstacles into avenues of approach for the enemy. d. Observation and Fields of Fire. Warmer temperatures in spring will create (1) Observation. Arctic air is exception- thaws and mud in the subarctic, causing rivers ally transparent, providing visibility and streams to overflow. In mountainous or over long distances. There is a lack of hilly country, landslides can be expected in the contrast between objects, however, spring, as the result of boulders and smaller particularly when they are covered rock formations expanding from the warmth by a layer of new snow. Observation of the thawing temperatures. in the Arctic is restricted chiefly by fog, blowing snow, and local smoke. c. Manmade Features. In the subarctic, The latter is a serious problem only routes of communication and transportation in the vicinity of larger settlements, are affected by every heavy snowfall and traf- where it often accompanies the shal- fic may come to a halt. Strong winds cause low radiation fogs of winter. A radi- snowdrifts requiring a constant clearing of ation fog results from the radiational routes, and transportation is slowed greatly cooling of air near the surface of the by ice and sleet. To avoid these drifts, roads ground on calm, clear nights. Depth may be routed through woods, where drifts perception is adversely affected by seldom occur, or along the crest of high ground arctic conditions, principally by the where the snow usually is less deep. In ex- extremely clear, dry air, the lack of tremely cold temperatures, railroad operation color differences, and the diffusing is restricted. Blocked tracks and derailments effect of light on the crystalline sur- are frequent; switches often are frozen; snow face of the snow and ice. A hazardous and rock slides, washouts, and frost heaving phenomenon that reduces visibility to damage the lines; and the ice caused by water near zero is the whiteout. When this seepage must be cleared from tunnels before condition exists, the horizon, shadows, they can be used. Excavation is difficult in and clouds are not discernible, and either frozen or thawed ground. In frozen only very dark objects can be seen. ground, handtools are ineffective. Explosives The amount of light reflected from a are effective, but they must be employed in snowcovered surface is much greater quantities greater than required in other ter- than that reflected from a darker rain. Gravel is easier to excavate than soil, surface, and accordingly the sun pro- because it has better drainage and accordingly vides greater illumination in the does not freeze as solidly. Foxholes, trenches, Arctic than in other regions. When breastworks, and emplacements may be pro- the sun is shining, sufficient light is vided by digging into the snow or through it reflected from the snow almost to into the underlying ground. Snow trenches eliminate shadows except in polar usually need revetting. In very deep snow, tun- areas where the shadows are quite nels may be dug to provide concealment. They long when the sun is shining. This furnish cover from small arms fire, but do not causes a lack of contrast, making it give protection from artillery fires. The spring difficult for the observer to distin- thaws in subarctic climates must be considered guish the outlines of objects even at when planning structures and fortifications. short distances. The landscape may Bunkers, trenches, and other field fortifications appear as a featureless grayish-white must be designed and sited so as to insure good field. Dark mountains in the distance drainage. In the thawing period, roads in low- may be recognized but a crevasse im- lying areas and bridges are apt to be washed mediately in front of a mountain may out. Floating ice will destroy or damage be undetected because of the absence

41 of contrast. There is good illumina- obscures projectiles and bursts. A tion from a full moon, and even the round bursting on impact in deep stars create considerable illumination. snow appears as a small white splash, Only during periods of heavy over- making sensing extremely difficult. cast does the arctic night approach Because of the cushioning effects of the darkness of other regions. A fog the snow, mines may fail to detonate. condition peculiar to the arctic cli- The clear air and snow cover may mate is ice fog. This is composed of increase the thermal radiation effect minute ice crystals instead of the of nuclear detonations in flat terrain water droplets of ordinary fog. Ice fog and snow shelters will be vulnerable forms in very cold, still air in a shal- to blast effects. Heavy snow and hard- low layer next to the ground. It is to-maneuver terrain will slow troops almost always present at temper- in traversing areas contaminated by atures of -45°F to -50°F in the vi- induced and residual nuclear radia- cinity of a source of water vapor and tion. When used in deep snow, im- remains as long as these conditions pact-detonating chemical ammunition persist. Where the smoke from build- burns in the snow and the chemical ing chimneys contributes water vapor agent tends to be smothered by the to cold, still air, ice fog may form at snow. Toxic chemical munitions pro- temperatures as high as -200 F. duce less vapor concentration because When the temperature increases of the low temperature and the rather than decreases with height smothering effect of the snow. On the through a layer of air, it is termed an other hand, low temperatures increase inversion. The strong temperature in- the persistency of toxic chemical versions present over the Arctic dur- agents in both vapor and liquid form. ing winter cause several phenomena Decay of biological agents is not as that affect observation. Sound tends rapid in arctic areas as it is in tem- to carry great distances. Light rays perate or tropical areas. are bent as they pass through the in- e. Cover and Concealment. The snow-covered version at low angles, often causing terrain offers few features that provide ade- objects beyond the horizon to appear quate concealment and cover. Tracks in the above it. This effect, termed looming, snow are almost impossible to hide, and dirt is a form of mirage. on fresh snow can be observed at a great dis- (2) Fields of fire. The fields of fire of tance. Due to the high visibility, effective automatic weapons are subject to the camouflage is difficult. Because of the difficul- effects of wind and snow and the final ties of concealment, night movements are protective line fires may be rendered frequently advisable. ineffective by snow drifts. Impact f. Obstacles. During the winter months, the bursts of high trajectory light artil- lakes, swamps, and rivers are frozen over and lery, mortar, and hand grenade fires cannot be employed as natural obstacles. Arti- are rendered relatively ineffective by ficial obstacles may be devised by freezing the cushioning effect of deep snow; large masses of snow or icecrete (a dense heavy artillery, however, remains frozen mixture of water, sand, and sometimes, highly effective. The employment of gravel) into desired shapes, or by icing deep proximity or mechanically timed air drifts. Roadblocks may be made by icing a bursts and overhead fire usually is section of the road, preferably one which the advisable. Because of the lack of iden- enemy must approach on an upgrade. Tank tifying objects and landmarks on traps may be devised by cutting the ice on a snow-covered terrain, the adjustment lake or river, then allowing it to refreeze of fire is difficult. Registration fire slightly. with air observation and by sound g. Avenues of Approach. Winter is generally and flash is hampered, since the snow the best time to travel in the Arctic and sub- 42 arctic, since the lakes, streams, and muskeg 100 centimeters (40 inches) deep without the areas are frozen over. Frozen rivers and water use of snowshoes and skis. Hard-packed snow, ways often become the best routes of advance however, is not difficult for troops to negotiate. and lines of communications during the winter With reasonable care lakes and streams may months. In general, most vehicles are immo- be crossed by vehicles in winter. The ice first bilized in snow from 1 to 1.5 meters (3 to 5 must be checked for thin spots, cracks, and feet) deep. The consistency of the snow, pressure ridges. During the spring thaws, whether it is dry and loose, moist, or packed, movement in ice and snow across tundra is affects the mobility of vehicles to a great ex- difficult and dangerous and cross-country tent. Tracked vehicles usually can move at low movement is practically impossible. After the speeds in packed snow that is no more than 1 snow cover has melted from the ground, both meter (3 feet) deep. After a packed snow trail wheeled and tracked vehicles can move rela- has been formed by the passage of several tively freely on it as long as the surface re- heavy vehicles, normal speeds may be main- mains frozen. This layer of ground that thaws tained. A thaw or the passage of a great many in the summer and freezes again in the winter vehicles on a relatively warm day will melt the is termed the active layer. As soon as the active snow surface, resulting in a coating of glare layer has melted, the tundra cannot support ice. The road then becomes practically impass- heavy concentrated loads and ordinary vehicles able to tracked vehicles unless ice cleats are will bog down. Even special-purpose vehicles installed on the tracks or the road is sanded. become roadbound during the thaw period and Foot movements are slow in 50 centimeters (20 cannot move across the tundra. inches) of snow and impossible in more than

43 CHAPTER 5

NATURAL TERRAIN FEATURES

Section I. SIGNIFICANCE

51. Definitions in a region with given conditions as to climate a. Topography. Topography refers to the and as to kind and structure of rock. The indi- physical features, both natural and manmade, cations of relative elevations given are to af- of the earth's surface. In terrain analysis, the ford specific definitions for the purposes of this following categories of topographical features manual. Other distinctions may be found in are considered: relief, drainage, surface mate- other references. A complete study of a land- rials, vegetation, special physical phenomena, form includes determination of its size, shape, and manmade (cultural) features. Terrain re- arrangement, surface configuration, and rela- fers to a consideration of topography in terms tionship to the surrounding area. of military significance. Weathering and ero- c. Relief. Relief refers to the irregularities of sion play a major role in shaping natural fea- the land surface. Local relief indicates the dif- tures (fig. 13). Weathering comprises the ef- ference in elevation between the highest and fects of the weather elements and erosion lowest points in a limited area and the size of includes the action of running water, waves, this area depends upon the purpose for which moving ice and snow, and wind upon rock and the surface is being considered. In terrain soil. studies, it is usually five square miles. Relief b. Landforms. Landforms are the physical features are the individual forms of the land expression of the land surface. The principal surface, such as hills or ridges and major re- groups of landforms are plains, plateaus, hills, lief features are plains, plateaus, hills and and mountains. Within each of these groups mountains. Minor relief features include: there are surface features of a smaller size, (1) High ground-swells, knolls, mounds, such as flat lowlands and valleys. Each type knobs, hummocks, hillocks, spurs, results from the interaction of earth processes ridges, buttes, mesas, and dunes.

Figure 15. Landforins caused by erosion in arid climate (a) Pinnacle. (b) Butte (Grand Canyon, Arizona).

44 (2) Depressions-gullies, draws, gulches, major factor influencing the commander when wadis, ravines, gorges, arroyos, can- deciding upon position defense or a mobile yons, and basins. defense. When the terrain restricts the ability (3) Breaks in high ground-saddles, of an attacking enemy to maneuver and pro- notches, cols, passes, cuts, and gaps. vides natural lines of resistance, a position de- (4) Special features-alluvial fans, talus fense may be desirable and of course, terrain slopes, talus cones, and boulder fields. that facilitates maneuver by defending forces will favor a mobile type of defense. In selecting 52. Military Operations the key areas for defense, the commander de- a. Influences. Terrain influences strategy and pends largely upon a terrain study. In addition, tactics. What aspects of the terrain are most a terrain study frequently will give valuable important at any given time will depend upon indications of probable enemy assembly areas, the particular requirements of the command field and air defense, artillery positions, ob- concerned. Logistic requirements, for example, servation posts, and avenues of approach. may emphasize the importance of communication centers, routes and rail nets, and water- d. Retrograde. In retrograde, good observa- ways. The tactics of a large-scale campaign tion and fields of fire permit engagement of may be dictated chiefly by the barriers im- the enemy at long ranges. Natural and arti- posed by major rivers and lakes, mountains, ficial obstacles are exploited to strengthen de- forests, or swamps. fenses, protect exposed flanks, and impede the of enemy advance. Concealment and cover are b. Attack. In the attack, the correct use essential for assembly areas and routes of terrain increases fire effect and diminishes losses. Dominant terrain forms the framework movement. Road nets are exploited to expedite of the system of observation, which in turn the movement of friendly forces and to facili- directly determines the effectiveness of sup- tate control, and are denied to the enemy for the same reasons. The effects of weather on porting weapons, the disposition and control of the terrain influence observation, trafficability, the attacking forces, the selection of objectives, and protective measures. Broken terrain, control, and the performance of troops and dense woods, built-up areas, and abrupt equipment. changes in elevation hinder the offensive em- e. Nuclear. The maximum effects of a nu- ployment of armor but afford cover and con- clear weapon are subject to many variables, de- cealment for infantry. Open, rolling terrain, pending on how the weapon is employed. Blast although providing little cover and conceal- and thermal effects would extend to a greater ment for infantry, is suitable for rapid ad- distance in open terrain, but the missile effect vances by armored formations. Soil traffic- and thermal fires obtained with a certain ability may be a determining factor in select- height of burst could create many adverse con- ing type of attack or an avenue of approach. ditions, such as tree blowdown, induced radia- c. Defense. The nature of the terrain is a tion, and immediate residual radiation.

Section II. LANDFORMS 53. Plains of feet above sea level and others are at sea a. Definitions. As a landform group, plains level. Some are rough and rolling and others are generally flat to rolling areas with uplands are flat. Because of their low degree of local or interstream areas less than 150 meters (500 relief, plains generally have low angles of feet) above adjacent valley bottoms. A dissected slope. In temperate climates, this characteris- plain is one with a surface that is interrupted tic makes them favorable for transportation by erosional features, and an undissected plain routes. Where there is monsoon weather or a is one with a smooth uninterrupted surface. tropical climate, however, more reliable routes b. General Characteristics. Plains may be may be provided by higher terrain. The details situated at any elevation. Some are thousands of relief include uplands and lowlands, ridges

45 and valleys, and hills and hollows, all within c. Classification. Plains are classified as- local ranges of elevation of 150 meters (500 (1) Flat. Local relief of less than 15 me- feet) or less. ters (50 feet).

Figure 14. Coastal plain formed by volcanic lava (Hawaii).

I - I- "o2w , . · (i ~~ N.~~ __ - .. . - -I~;-- I - .l L·: --.-- _. I'' . , _'

Figure 15. Outer delta features (Moses Point, Alaska).

46 0 5t 0

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00 a

'IC

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47 (2) Undulating. Local relief of 15 to 45 Cuestaform coastal plains are characterized by meters (50 to 150 feet). long, low ridges alternating with lowlands in (3) Rolling. Local relief of 45 to 90 me- bands several miles wide and many miles long ters (150 to 300 feet). generally parallel to the coast. The ridges on (4) Roughly dissected. Local relief of 90 this 'type plain are usually asymmetrical, the to 150 meters (300 to 500 feet). steeper slope being inland. (5) Slope. In terms of slope, plains are e. Delta Plains. These plains, which are considered smooth when they have formed by sediments deposited at the mouths large areas with a slope of less than of streams and rivers, are usually low and 2 percent, and rough when there are marshy, with a local relief of less than 15 me- large areas with a slope of more than ters (50 feet) (fig. 15). The features of great- 2 percent or many small areas with est relief are the natural levees, which are low, steep slopes. broad banks of alluvium on either side of the d. Coastal Plains. These are generally low stream channels. For protection against stream and featureless (fig. 14). Frequently they have overflow, artificial levees may be built near the shallow valleys formed by streams that origi- stream on top of the natural levees. nate inland. Swamps usually are numerous. f. Flood Plains (fig. 16). These, also called

Figure 17. Meandering river, showing flood plain and oxbow lakes. 48 OLD ALLUVIAL PLAIN NOW EXISTING AS A TERRACE OXBOW LAKE

FILLED MEANDER CHANNEL SURROUNDING HIGHLANDS ALLVIAL FAN /

Figure 18. Flood plain with evidence of pre-ezisting meander. alluvial plains, are formed by weathered and are classified as either ice scoured or drift eroded material deposited by streams upon the plains. floors of their valleys. The flood plain usually (1) Ice-scoured plains are level to gently is poorly drained, and may contain marshes, rolling areas composed largely of bare swamps, lakes, and former stream channels. rock. They are characterized by round. Unless protected by levees, it may become part- ed rock hills and broad open valleys ly or completely covered by water in times of and basins with comparatively low flood. The surface is flat, the levees alternating local relief. Over the valley floors with swamp areas. Meandering rivers and there may be a thin covering of glacial crescent-shaped (oxbow) lakes are characteris- debris which serves as an anchorage tic of this type plain (fig. 17 and 18). The silts for shallow-rooted trees, chiefly coni- and clays deposited on flood plains make pro- fers. There are numerous falls, rapids, ductive soils, and this type plain is used ex- and lakes. Some small shallow lakes tensively for agriculture. become filled with remains of marsh vegetation, such as sphagnum moss, g. Piedmont Plains. These are alluvial plains creating bogs of the type called formed by mountain streams with steep muskeg in Canada. gradients that deposit a sediment, consisting (2) Drift plains consist largely of boul- largely of gravel and sand, at the point where ders, gravel, sand, or the stream enters the lowlands. This type of clay in layers of varying plain is found in arid and semiarid regions thickness on top of other strata of rock and with meager vegetation and torrential rains. soil. The principal characteristic is a Although the plain may appear level, actually gently undulating it slopes away from the mountain base. Many surface which includes broad, low piedmont alluvial plains are covered only with hills, or swells, and wide, shallow depressions, or shrubs or sparse grasses. Those with fine soils swales. Commonly the are high in mineral plant fodds and, if irriga- local relief is less than 30 meters (100 feet). Large areas of drift tion water is available, they are suitable for plains are agriculture. essentially flat, with poorly developed natural drainage. Although soils are h. Glacial Plains. These (fig. 19 and 20) generally heterogeneous mixtures,

49 Figure 19. Glacial plain (Moose Jaw, Saskatchewan, Canada).

areas of impervious clays are com- are low, irregular ridges or hillocks. Numerous mon. After heavy rains, ponds several caverns are formed beneath the surface of a acres in extent may form; and unless karst plain, and there are also large under- artifically drained, the water may ground streams which may issue at the surface stand until it evaporates. In some lo- as springs of considerable volume. calities there are hills of clayey till called drumlins (fig. 21) that occa- 54. Plateaus sionally reach heights of more than a. Description. A plateau is commonly bor- 30 meters (100 feet) and may be a dered by an escarpment or steep slope on at mile long. Streams in this type of least one side. The plateau surface may be cut plain may be interrupted by swamps, by deep, narrow stream valleys, but the inter- lakes, falls, or rapids. stream areas are mostly broad and nearly level. i. Lacustrine Plains. These are formed by Tabular uplands with a local relief of more sediment settling on lake bottoms. Subsequent- than 150 meters (500 feet) may be considered ly the lake was drained by natural forces, or plateaus. They vary greatly in configuration, evaporated because of a major change in cli- but most have broad flat surfaces high above mate. They are level and often contain salty or sea level, and are deeply trenched by narrow alkaline lakes. Generally they are character- valleys. Depending upon the stage of the ero- ized by poor drainage and alkaline soils. sion cycle, the valleys that dissect the plateau j. Loess Plains. These are formed by wind- may be widely spaced early in the cycle or very blown particles of silt, called loess, which have closely spaced late in the cycle (fig. 24). Most been deposited over large areas, forming a large plateaus are in regions with arid or semi- smooth, gently sloping surface. The ability of arid climates. Plateaus may be classified into loess to stand in vertical walls results in steep three major types: escarpments along gullies, stream valleys, and (1) Intermountain (fig. 25). Surrounded artificial cuts (fig. 22). or nearly surrounded by mountains. k. Karst Plains. These (fig. 23) are a type (2) Piedmont. Lying between mountains of erosional plain developed on limestone. They and plains, or between mountains and have a pitted surface along with exposed bed- the sea. ding plain edges (pinnacles) tilted through the (3) Continental (fig. 26). Rising abruptly surface. The pitting is formed from subsurface from bordering lowlands or the sea collapsing due to the solvent action of under- on most or all margins; usually with- ground water. Between the depressions there out conspicuous mountain rims.

50 I:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I kl-X:,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

51 Figure 21. Drumlin (New York).

b. Climates. In arid climates, streams usual- Greenland produce marginal features ly flow in canyons cut into the plateau, the which are different from those of typical canyon having a narrow bottom offer- Antarctica. The ice is confined by the ing little space for a roadway. The stream is highlands, melting some distance in- seldom navigable and follows a steep, boulder- land on the southern and western strewn course interrupted by rapids and falls. margins. Where ice does not discharge Sudden and extensive changes in stream level into the sea, it protrudes through gaps are common. Canyons usually are too deep to in the bordering highlands (fig. 27). be crossed easily and too wide to be bridged Irregular icebergs form, drifting into economically. They rarely provide a transpor- the Atlantic Ocean during the spring tation route and are a difficult obstacle to months. movement. Areas between the streams usually (2) Marginal features of Antarctica. The are flat or rolling uplands, some of vast extent. marginal ice of Antarctica is thin and Areas of interior drainage called bolsons exist traversed by deep cracks. Except in on some plateaus. The streams empty into a few localities where it is retained these, resulting in level areas that may contain by the fringing mountains, the ice large salt lakes or salt marshes. Plateaus in overruns the land margins, so that the humid climates tend to be more dissected by exact position of the continental stream erosion than those in arid climates. shoreline is not known. The edge of Broad divides with rounded and irregular up- the ice is marked by sheer cliffs. From lands are common. these cliffs giant icebergs split off c. Ice Plateaus. The vast sheets of ice that along crevasses as a result of under- cover most of Greenland and Antarctica may cutting by waves and the buoyant ef- be regarded as great plateaus. Greenland is fect of sea water. Some of these are an intermontane plateau, surrounded by a tens of square miles in area. The ice- fringe of mountains. In most of Antarctica, bergs disintegrate by melting and the ice rises in a sheer wall, then slopes up disperse as masses of floe and drift rapidly to a fairly level interior with an aver- ice which fringe the continent for age elevation of about 1,830 meters (6,000 many miles. feet), the maximum elevation of 3,050 meters (10,000 feet) being found in regions inland 55. Military Effects of Plains and Plateaus from the Pacific coast. In general, the surfaces a. Variety. Although plains and plateaus are of an ice plateau are flat or have parallel characterized by relatively low relief compared ridges a few feet in height which result pri- to hills and mountains, they present a wide marily from the wind and drifting snow. variety of topographical conditions. Since (1) Marginal features of Greenland. The each type of plain or plateau differs in its fea- highland or mountainous rim and the tures and effects, one can only generalize about higher summer temperatures of their influences on military operations.

52 i~~~~~~~~~~~~l

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Figure 23. Karat plain (Canada).

Fi- a

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Figure 24. Plateau dissected by stream (Deschutes River, Oregon).

b. Movement. unfavorable soil conditions and dense (1) Coastal plains. In general, the topog- vegetation in areas of medium to raphy of coastal plains offers no ma- heavy rainfall. Movement along an jor obstacle to the cro,ss-country indented shore usually is difficult be- movement of tracked vehicles, al- cause the terrain is separated into though there may be areas that are compartments by streams and estu- difficult or impracticable because of aries. Cross-country movement in-

54 I __ - n _ ~~'!",~~ 7 Z 'W~~; f,4 t '4'i42p 111),,1el' 'I

2. C

Figure 25. Intermnountain plateau (Jackson Hole, Wyoming).

land may be limited to narrow areas as avenues of approach by the enemy bordered by water. In such terrain, must not be overlooked. attacks may require amphibious sup- (3) Alluvial Plains. The stream valleys in port. Coasts with beach ridges hinder alluvial plains generally provide cor- an advance inland because vehicles ridors through areas of greater relief. must cross poorly drained areas be- In dry weather, the cross-country tween relatively stable sand ridges. movement conditions usually are ex- Terrain of this type impedes the ade- cellent, except for such obstacles as quate dispersal of troops and supplies. streams and local areas of unfavor- (2) Delta plains. On delta plains cross- able soil or dense vegetation. In wet country movement usually is hindered weather or during floods movement by marshy ground, shifting streams may be limited to small areas of with loose sand and mud bottoms, higher, better-drained ground, such as and thick vegetation. Soils are better levees. Alluvial terraces are above drained in the inner regions of the flood levels and may be well-drained, delta. Normally the natural levees of but they are commonly isolated by streams provide the highest, best- steep slopes. It is not unusual for a drained, and most trafficable parts of stream to meander from one side of the delta. Movement on the low-lying its valley to the other. If the valley grounds of delta plains is always slopes are steep, such meandering threatened by the possibility that the may eliminate vehicular movement enemy will destroy dikes or levees and up or down the valley. flood the area. The use of waterways (4) Glacial plains. The topography of

55 'Cur" X iRB . g'. i·Ija ;a* E *E ' He'' --- '-i

W_nj4 _>

Figure 26. Eroded continental plateau (Grand Canyon, Arizona).

glacial plains usually presents no in- level surface of lacustrine plains (old surmountable obstacles to movement. lake beds). During wet weather, Large boulders may be obstacles in however, the fine soils may be slow- some area. In regions containing large drying and become nontrafficable areas of soft ground, lakes, or (fig. 29). marshes, movement in the rainy sea- (6) Loess plains. Loess is a fine-grained, son may be greatly hindered by mud yellowish-brown silt deposited by the (fig. 28). wind. In dry weather, movement con- (5) Lacustrine plains. No topographic ob- ditions on loess plains are good, ex- stacles to movement are offered by the cept where escarpments and ravines

56 ,,I*I.T( Pag ,-r - W0 e· -r

Figure 27. Tongues of icecap descending toward fiord (Greenland). are encountered. Ground conditions tion does not interfere, it may be good on the may become very poor in wet more level portions of these plains. Vegetation weather, making cross-country move- also determines the amount of observation that ment impracticable. may be secured in lacustrine, loess, and karst (7) Karst plains. Movement on karst plains. plains, a limestone region, is limited d. Cover and Concealment. Coastal plains chiefly by the sinkholes, which may provide few areas with sufficient cover and have steep slopes and contain swamps concealment for larger units. Except for the and ponds. In wet weather the clayey levees, there are also few topographic features residual soil overlying the limestone on delta plains that will conceal or protect may limit movement in some areas. troop bodies of any size. Little cover and con- Karst regions vary greatly in their cealment are available on alluvial plains, ex- characteristics-from a plain with an cept for that provided along terraced scarps, occasional sinkhole to a surface so river banks, and levees. On glacial plains, cover pitted and broken as to make even is lacking in the more level parts, but there dismounted movement very difficult. may be some limited cover and concealment Knowledge of the erosional develop- provided by knobby and forested areas. The ment is necessary to evaluate such an sinkholes of karst plains also provide a moder- area properly. ate degree of concealment and cover. c. Observation. The degree of observation e. Construction. available on coastal plains is normally good along the coastline, but inland the flat country (1) Coastal plains. Although generally and forest cover usually offer few observation there is no hard rock on coastal plains, points. Observation is limited on delta plains sand and gravel are abundant on because the low, level ground generally is cov- beaches and along streams. The ered thickly by vegetation. On alluvial plains, ground of coastal plains is excavated observation from the valley bottoms usually is easily, but the depth of excavation poor, but the bordering regions provide com- usually is limited by the high water manding views into the valleys. Where vegeta- table. Long and straight road aline- 57 Figure 28. Glacial boulders (Yo8emite National Park). ments normally can be obtained. water table limits underground re- There are many suitable sites for air- turn. Accordingly, drainage and fields, particularly along the marine pumping systems may be required. terraces. (3) Alluvial plains. Rock is scarce in flood plains. Abundant sand and fine (2) Delta plains except where it may crop out binder material may be obtained on along the scarps of terraces. Sand, delta plains, but gravel is scarce. gravel, and binder material are abun- There are no exposed hard-rock for- dant along stream channels and the mations or bedrock. Generally the terrace scarps. Terraces also may pro- location of airfields and roads must vide suitable sites for bunkers and be confined to the levees. Structural underground installations. Excava- foundations not built upon levees are tions in flood plains are limited by unreliable, and may settle due to the the high water table, but these plains low, poorly-drained ground with a and terraces if well-drained are suit- threat of periodic flooding. Drainage able for the construction of roads and always is a serious problem because airfields. the levees prevent the return of surface water to the river, and the high (4) Glacial plains. Sand and gravel are

58 7i0

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59 widely distributed on glacial plains, (3) Major interruptions (hills, moun- and rock usually is abundant. On till tains, river valleys). plains, boulders may provide building (4) Minor interruptions (gullies, stone, but there is bedrock only in a sinks, few locations, such as in deep valleys levees). where the overlying till has been cut b. Plateaus. through. Wet ground and weak soils may create foundation problems (1) Area covered by plateau. where the drainage is not good. (2) Surface (elevation, slope, surface, re- (5) Lacustrine plains. Except at the mar- lief features). ginal slopes, where sand, gravel, and (3) Major rock may be obtainable, lacustrine interruptions (hills, mountains, canyons, valleys). plains usually can provide only clay and fine sand for construction pur- (4) Margins (mountains above plateau, poses. The fine-grained soil makes a abrupt descending cliffs). poor foundation for structures, particularly in humid climates. Lacus- 57. Mountains trine plains provide level sites for airfields with few natural obstructions a. Description. As a landform group, moun- and allow unrestricted road aline- tains are rugged areas with crests that are, ments. in general, more than 600 meters (2,000 feet) above adjacent lowlands. They are commonly (6) Loess plains. Loess plains are a poor distinguished from other major source of gravel or rock, except where relief features by the predominance of slopes and there are underlying deposits. their overall Foun- massiveness. dations require In terms of local relief, moun- stabilization and in tains may be classified as low when they have cold climates the loess may heave. In a local relief of 900 meters (3,000 dry climates, thick Ioess deposits are feet) or less, and high when their height exceeds that easily excavated and are well suited figure. According to their size and arrange- for underground installations. Many good airfield ment, mountain features may be classified as sites and road alinements peaks, ranges, chains, and cordilleras. usually are available. (7) Karst plains. Large quantities of b. Peaks. A peak is a conical high mass, that limestone for building stone and rises above its surroundings. Ordinarily a peak crushed rock may be obtained on is a feature of minor order upon a range, but karst plains. Sand and gravel usually as in the case of an isolated volcanic cone, one are lacking. Excavation often is dif- peak may stand alone and comprise the entire ficult because of the irregular rock mountain mass. surface, with deep clay-filled pits, and the high pinnacles of rock that lie be- c. Ranges. A range is an arrangement, neath the residual soil. Grading usu- usually linear, of many peaks, ridges, and ally requires the excavation of rock. their valleys. The term ordinarily applies to There is always a possibility of foun- mountains that have a general unity of form, dation subsidence. structure, and geologic age. d. Mountain Chain. A mountain chain con- 56. Information Requirements - Plains and sists of several associated ranges, usually more Plateaus or less parallel, having unity of position, form a. Plains. or structure, but separated by trenches or (1) Extent of area covered by plain. basins. (2) Surface (elevation, slope, kind of sur- e. Cordillera. A cordillera is a large regional face). grouping of mountain chains.

60 58. Mountain Features 59. Hills a. Relief. Mountains are distinguished from As a broad landform group, hills are rough hills by their greater relief, more rugged con- areas with crests generally from 150 to 600 tours, and more complicated surface patterns. meters (500 to 2,000 feet) above adjacent low- The average slope of large mountains seldom lands. They usually contain a predominance of is more than 20 ° to 25 ° from the horizontal, moderate slopes. Hills may be classified as and only a few have slopes of more than 35 ° low when they have local relief of from 150 near the summit. Even walls that seem vertical to 300 meters (500 to 1,000 feet), and high, seldom have slopes that average more than 70 ° . when the local relief is from 300 to 600 meters (1,000 to 2,000 feet). Some very rough hills b. Valleys. Except where they have reached may appear mountainous in relation to adja- grade level and meander in flat alluvial valleys, cent plains, and locally may be called moun- mountain streams have high gradients and tains, but they are not properly of a size or flows of high velocity. The rapid downward nature to merit the term. Mature hill lands cutting action of the stream may uncover bed- may be almost entirely a succession of hills, rock of unequal hardness, so that falls and valleys, and narrow ridges, with level land oc- rapids develop. Some streams, in cutting cupying less than five percent of the total area. through bedrock of unequal resistance, erode Hill regions in an early stage of erosion may valleys which are broad at their headwaters, include some fairly level, plateaulike uplands then narrow to gorges, and subsequently open separated by steep-sided valleys. Those in a out again downstream. Valleys formed by more advanced erosional stage may have broad glacial action have wide rounded bottoms and open valleys and reduced slopes that are suit- steep sides. They have U-shaped profiles, in able for agriculture. Because some of the slopes contrast to the V-shaped profile of a stream in hill regions are steep and untillable, they eroded valley. The walls are steep and rugged. have retained their forest cover and have Most glaciated valleys have one or more basins streams with steep gradients that are capable in which impounded drainage creates lakes, of developing waterpower. ponds, or marshes. c. Divides. Between the mountain valleys 60. Military Effects of Hills and Mountains there are uplands formed by remnants of the a. Key Terrain Features. In both attack and original elevation. Rainfall on these uplands defense, the key terrain features may include separates according to the surface slopes and the heights which dominate valleys, the routes descends by numerous rivulets into adjacent of communications, passes and valleys which valleys, modeling the uplands as it flows. The permit cross-country movement through the uplands are called divides. When they separate mountains, and aircraft landing areas. Domi- the drainage destined for opposite sides of a nating heights which may be used by the continent they are termed continental divides. enemy for observation of avenues of approach must be controlled. d. Foothills and Spurs. The lowest and least massive features of mountain uplands are the b. Observation and Fields of Fire. foothills and spurs that fringe the principal (1) Observation. In hilly and mountain- highlands. Foothills are hills located at the ous areas, observation may be re- base of higher mountains or hills. A spur is a stricted. In most cases, commanding ridge projecting laterally from the main crest heights provide only partial observa- of a hill or mountain. tion of adjacent valleys and slopes. e. Passes. The erosion by streams or glaciers Foothills and spurs extending into a creates saddle shaped notches, or passes, in a valley obscure observation along the mountain barrier. The term pass is applied to valley. any type of natural passageway through high, (2) Fields of fire. Mountains and hills difficult terrain. place some restrictions upon the em- 61 ployment of supporting weapons. Ar- or up valleys in the daytime, may de- mor loses much of its mobility because flect the clouds or reverse the forecast it cannot move across country. Occa- flow; likewise they may produce fa- sionally tanks can be used in small vorable conditions for cloud travel. numbers against limited objectives, c. Cover and Concealment. The rugged to- but their action often is confined to pography of mountains offers abundant cover providing direct fire support. Artil- and concealment, although movement across lery is effective, but the limited visi- slopes or crests above the timberline will be bility in mountainous terrain restricts exposed. Sounds carry from valley bottoms to observation and adjustment of fire. hilltops, but within the valley, sounds are muf- Terrain features may also reduce the fled by ground forms and streams. effectiveness of air defense artillery by making radar siting difficult and d. Obstacles. Major obstacles to movement reducing the target acquisition range include steep, high ridges and ranges, high of the system. Survey and fire control valley routes and escarpments, sloping cliffs are hampered, and more time is re- and terrace faces. Minor obstacles include quired for artillery to displace. There stream embankments, valley terraces and is difficulty in finding gun positions benches, spurs, talus, and debris-choked valleys, that do not have too much defilade. and presence of boulders. The heavier crew-served weapons of the infantry and their ammunition e. Avenues of Approach. Hills and moun- are difficult to carry over the rugged tains parallel to the axis of advance offer flank protection, but limit lateral movement. When terrain. Mortars and recoilless rifles perpendicular to the axis, they are an obstacle are effective and are favored for op- attacker and an aid to the defender. erations in mountains and hill regions. to the the Deep valleys and ravines afford a Mountain roads must be improved because degree of protection from the blast roads are generally narrow, have steep grades, and poor surfaces. Sharp turns may prevent effect of nuclear weapons when the axis of the valley or ravine points the use of trailers. Roads in valleys or along well away from ground zero. When it defiles require that the adjacent high ground control of the roads. does not, there is little or no shielding be secured to insure Mountain roads are subject to slides and may effect, and blast damage may be increased because the blast is canalized. be blocked by snow. Those on the crest of Deep valleys and ravines afford sub- ridges may be exposed to enemy observation. stantial protection from thermal and Roads in defiles may be flooded and may also have large boulders. The best sites for military nuclear radiation to troops, materiel, roads in mountain areas are normally on the and buildings located within the sides of slopes. shaded portions. In terrain characterized by deep valleys and ravines, f. Communications. Hills and mountains con- however, blast effects of nuclear tain dead spaces that often limit the range weapons may cause serious avalanches and effectiveness of radios, although these re- and rock slides. Concentrations of strictions usually can be overcome by the use toxic chemical agent aerosols are ex- of relay sets. Wire laying is difficult, and visual tremely hard to achieve on marked signals are not always dependable and often downward slopes. Toxic chemical can be seen by the enemy. agents and biological agent clouds g. Air Support. The hazards in mountainous tend to flow over rolling terrain and regions place limitations upon the use of low- down valleys, to remain in hollows flying combat aviation. Targets are difficult to and on low ground and in depressions, locate and in many cases close air-support but to go around obstacles. Local strikes must be controlled by aerial FAC's winds, coming down valleys at night (Forward Air Controllers) or by indirect 62 means, since the functions of tactical air- mating the probable effect of fire on rock control parties are hindered by the terrain and fragmentation, and determining the possible weather. ricochet effects of projectiles. The soil usually is thin or stony, with underlying bedrock, so h. Combat. Combat in mountains and hilly that it is difficult to construct field fortifica- areas usually consists of a series of independent tions. Geologic study will assist in selecting actions to seize and hold key terrain, strike areas where excavations may be made and in communication lines, and protect friendly choosing the required explosives and equip- routes of supply and evacuation. Infantry plays ment. the dominant role, since it is not roadbound and can close with the enemy under any con- 61. Information Requirements - Hills and dition of terrain. Commanding positions in Mountains mountain terrain are often rocky ridges or eminences with little or no soil. If the im- a. Extent and Type of Mountains or Hills. portance of the position justifies the time and b. Ridge Crests. effort required, trenches, emplacements, and (1) Location and orientation. galleries can be cut into the solid rock. Parapets and breastworks of cobbles and boulders are (2) Elevations (typical, highest, lowest). effective against small arms, but they are (3) Height above adjacent valley flats vulnerable to artillery fire. Log breastworks (average, highest, lowest). and protective shelters may be built if timber (4) Pattern (lo n g straight, parallel stands are conveniently located. Mines and ob- ridges; branchlike and crooked ridges; stacles find their most important use in ob- clusters of knobs and peaks). structing movement on roads and trails and through defiles. Roadblocks are effective (5) Skyline (flat-topped and broad, or because of the difficulty of bypassing them. knifelike). Mountain terrain favors the defender because c. Slopes. available obstacles enable him to use minimum troops to deny the attacker the use of existing (1) Shape (convex, concave). routes. He can force deployment of major (2) Angle, in percent or degrees (near enemy units and the expenditure of large crest, middle, near base). amounts of mortar and artillery ammunition, (3) Minor relief features (rough lava, and can inflict the maximum punishment from boulder fields and gullies). protected positions. d Valley Flats. i. Construction. Hard rocks suitable for con- (1) Location. struction purposes are readily obtained in hills (2) Width (of main and tributary val- and mountains. Sand is scarce, but gravel may leys; average, widest, narrowest for be secured in the lower stretches of streams both categories). where they approach the foot of the mountains (3) Pattern (long, straight, and parallel or flow through hills. There are few suitable valleys or branchlike and crooked locations for airfields because of the difficulty valleys). of excavation in rock, the obstructed and limited approaches, the poor accessibility, and the (4) Transverse profile (degree of slope turbulent air currents. Highways, railways, near center and margin of valley). and tunnels are vulnerable in these areas. (5) Longitudinal profile (degree of slope Geologic data may be useful in indicating rock near mouth and head of valley). conditions favorable to initiating rock slides (6) Terraces (benchlands) along borders by bombing or artillery fire to block enemy of valley flats (number of terrace lines of communication. Geological information steps, width, continuity, elevation of will also assist in selecting sites for gun em- steps one above another, slope be- placements and other fortifications, in esti- tween terrace levels).

63 (7) Stream channels within valley of steps above one another, slope be- (straight or meandering, bordered by tween terrace levels). bluffs, gentle downslopes, or natural f. Passes. levees). I (1) Location. e. Intermontane Basins. (2) Elevations (average, lowest, highest). (1) Location. (3) Number of passes (distance between (2) Width (average, widest, narrowest). passes). (3) Shape (round, oval, long and narrow, (4) Gradients (near head of pass, down- irregular). slope). (4) Flat bottom lands (extent and loca- (5) When closed by ice and snow. tion). (6) Character of defile formed by pass and (5) Terraces (benchland) about borders approaches (width, length, character of flat bottom lands (number of ter- of slopes). race steps, width, continuity, elevation (7) Routes over each pass.

Section III. DRAINAGE

62. Effects of Drainage c. Patterns. Drainage patterns (fig. 30) reflect the subsurface structure. They are of a. Description.The water features of an area three major types--dendritic, trellis, and radial comprise its drainage. They include streams defined as follows: and canals; drainage and irrigation ditches; lakes, marshes, and swamps; artificial bodies (1) A dendritic drainage pattern is a of standing water such as reservoirs and ponds, treelike arrangement of streams found as well as such subsurface outlets as springs most frequently in an area underlain and wells. The character of these drainage fea- by homogeneous rock. tures is determined by precipitation, relief, (2) The trellis pattern results from the surface runoff and ground-water flow, and influence of tilted alternating strata various manmade improvements. Vegetation of weak and resistant rocks. The re- has a major influence upon drainage. Dense sistant strata separate each stream, grass and tree growth on slopes tend to slow producing the overall trellis effect. up and absorb a considerable amount of the (3) The radial pattern has streams that runoff, but slopes with few trees and sparse radiate from a central dome that lies vegetation permit rapid runoff and the forma- within a relatively flat area. tion of channels by erosion. b. Catchment. A catchment basin or catch- 63. Rivers and Streams ment area is the total area drained by a a. Perennial Stream. A perennial stream stream or system of streams. All water features flows throughout the year. The regular flow within this area are related and are considered may result from a spring lake or a glacier at as a whole. The limits of the drainage basin the head which furnishes a constant supply of are marked by the topographic divide which water, from direct precipitation of fairly con- separates it from neighboring drainage sys- stant quality, or because the beds are deep tems. The amount of water reaching the enough to be permanently below the fluctuating stream, reservoir, or lake depends upon the upper level of the ground water or water table. size of the area, the amount of precipitation, and evaporation and transpiration. The rate of b. Intermittent Stream. An intermittent evaporation depends upon the temperature, stream originates in a source of water that vapor pressure, wind, and solar radiation. fails periodically and is particularly common 64 ~~~O/g,~~~~~~~o-i~

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63 in semiarid regions with seasonal rain or snow- age net is centralized in interior basins. There fall. Some streams are intermittent because may be separate basins at different elevations they depend for supply upon the water table in each desert. Many large streams flow into and do not have beds deep enough to be inde- desert lakes that have no outlet, or disappear pendent of fluctuations in the table. through evaporation and seepage into porous c. Ephemeral Stream. An ephemeral stream surface material. Some streams encountered in is temporary, depending upon infrequent rain- deserts originate in humid regions, flow across fall for supply. the arid land, and then continue their course in another adjoining humid area. When pre- d. Bottoms. Rivers and streams deepen their cipitation occurs in desert areas, it is likely to beds by erosion of the underlying rock. As be in cloudbursts that generate a tremendous stream erosion continues, the velocity of the runoff as the water rushes down. Sheltered dry current decreases, with a resulting decrease washes or wadis may become extremely dan- in down-cutting potential. Eventually, the cut- gerous locations for bivouacs, gun positions, ting potential is balanced by the sediment load and installations during these brief but violent carried by the stream. Subsequently, unless floods. there is a change in the topography of the catchment basin, the stream alternates between 64. Lakes build-up and cutting down. Differences in the load carried by the water at different points, Some lakes are formed by glacial action in velocity caused by changes in grade, and in creating a depression which subsequently fills the degree of hardness of the rock make the with water, by the damming of a river by ice beds uneven, producing gorges, cataracts, rap- or a moraine, or by water filling a natural ids, and potholes. Where streams have a high depression as a glacier recedes. A stream may velocity and flow over loose materials, the bot- be formed into a lake because of interference toms commonly are rocky. In slow-moving with its natural course by a lava flow, dam, water, fine material such as silt and clay is or avalanche. Coastal lagoons frequently are deposited, and the bottoms will be muddy. formed by the deposition of silt or sand at the mouth of a river. The crater of an extinct e. Banks. As down-cutting potential de- volcano often collects water and becomes a creases, side-cutting begins and the river lake basin. Salt lakes occur when a lake is so widens its bed or develops a curving course. poorly drained that the minerals in the water As a rule, these curves will have steep banks remain while the water evaporates. In lime- on the outside and gentle, low banks on the stone country, lakes caused by the filling of inside. The conformation will vary with the depressions of dissolved rocks are common. composition of the bank, the velocity of the stream, and the kind of materials transported 65. Marshes and Swamps by the stream. Swift streams in rough relief commonly cut deep channels with low banks. a. Description. A swamp (fig. 31) is an area f. Flooding. Some streams flood annually and of saturated ground dominated by trees and others infrequently. Floods may be caused by shrubs. A marsh (fig. 32) is an area of satu- rapidly melting snow, by excessive precipita- rated ground dominated by grasslike aquatic tion and runoff, by ice jams, or by any com- plants. A bog is an area of soft, wet, spongy bination of these. When a river is in flood, the ground consisting of peat which supports velocity of water is greater than normal, with mosses, low shrubs, and in some cases poorly the fastest current in the main channel. developed trees. g. Desert Drainage. Arid climates have long b. Formation. Swamps, marshes, and bogs dry periods with infrequent precipitation. Des- are formed by the overflow of rivers, dams, ert streams for this reason are irregular in flooding by tides, a lack of balance between volume and duration of flow. Large areas of rainfall and runoff or seepage, impervious sub- many deserts do not have streams flowing out soil in level areas, or the spread of vegetation of their immediate vicinity because the drain- in lakes, particularly in oxbow lakes. They may 66 -~~~~u4

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Figure S2. Marsh (Foxholm, North Dakota). be numerous on delta and flood plains, where ice that moves slowly on a land surface. Glaciers surface water is not readily drained. Extensive depend on the receipt of an annual amount of marshes and swamps are encountered on the snow, and form only where there is a carryover plains of humid areas. In glaciated regions, of snow from one season to the next. Abundant marshes, bogs, and swamps are common. precipitation is more important than extreme cold. The ice is formed by the crushing of snow 66. Glaciers flakes from the weight of new snowfalls and a. Description. A glacier is a thick mass of shortly altered to a loose aggregate of rounded

67 granules of ice. With deeper burial these come frozen tightly in the sides and bottom granules are deformed, locally melted and re- of the ice. These fragments abrade the walls frozen and recrystallized, to produce a solid like a giant rasp. This abrasion scratches and mass of interlocking ice crystals. There are polishes the walls and straightens out the val- two types of glaciers: valley glaciers and con- ley.by grinding away irregularities on opposite tinental glaciers. sides. Narrow "V" stream valleys are reamed b. Valley Glacier. A valley glacier (fig. 33) out into much more even "U" shaped valleys. begins in the summit areas of the high mountains. Patches of snow are converted into ice- c. Ice Front. The lower end of a glacier, or fields. Those icefields at the heads of former the ice front, stands at that point where the stream valleys may eventually become thick supply of ice from up the valley is just equal enough so that the ice begins to move down- to the loss through melting and evaporation. ward following pre-existing stream valleys. As If supply is greater than loss, the ice front the glacier moves down the valley, rock frag- moves down the valley; if loss exceeds supply, ments become plucked from the walls and be- the ice front retreats.

Figure 33. Valley glacier (Alaskan coast. Kame terrace and outwash plain in right foreground). d. Debris. Rock debris carried in or on the cases the centers of accumulation lie at low glacier may be dumped at the ice front when elevations. Continental glaciers make extensive the ice melts. This material, called till, consists deposits dumped directly from the ice. End of an unsorted mixture of rock powder, pebbles, moraines mark positions at which the glacier cobblestone, and boulders. If the ice front re- edge stood for some time. They are long ridges mains stationary for a period of time, a ridge or belts of low hills that extend across the of till, extending across the valley, is formed. country for many miles. Large areas on the This ridge is termed an end moraine. glaciated side of the end moraines commonly receive a sheet of till plastered on the under- e. Continental Glaciers. Continental glaciers, lying rock. This ground moraine or till sheet such as those covering most of Greenland and was left behind as the heavily loaded ice sheet Antarctica, begin in one or more central areas melted away. of snow accumulation. The ice starts to move outward when it becomes so thick that the f. Meltwater. Streams of meltwater leaving pull of gravity on the mass exceeds the strength an ice sheet may flow down valleys that lead of the ice. No slope is required and in many away from the glacial front. The material pre-

68 viously left from frozen ice is deposited along ing through openings in the rocks, the water the stream valleys in the form of valley trains. issues at the surface as springs, streams, and Where the land surface slopes evenly away lakes. Ultimately all the water that is precip- from the edge of the ice sheet, meltwater itated returns to the atmosphere by evapora- streams may spread over the coufitryside in tion from water surface or from the foliage branching, braided patterns forming wide- of vegetation. Some also is released from fo- spread outwash plains. Outwash plains are liage by transpiration, the process by which composed of relatively well-sorted, evenly bed- a plant transmits water through its tissues, ded sand and gravel which may be many feet discharging water vapor from its foliage. thick and cover many square miles. Although this hydrologic cycle is irregular and may extend over a period of years, no water 67. Ground Water is lost permanently from circulation, but a a. Hydrologic Cycle (fig. 34). Water evapo- stage of the cycle may be bypassed or inter- rated from the ocean is condensed into clouds, rupted. Rain falling upon a heavily forested from which it falls to the earth as rain, snow, area, for example, may return directly to the sleet, or hail. Part of this water runs off into atmosphere by evaporation without going lakes and streams, or is retained by the soil, through other stages of the normal natural passing into underlying rock formations. Mov- process.

Figure 84. The hydrologic cycle. b. Water Table. When water fills the pores of the rock formations, amount of rainfall, and crevices of the underlying rock, a zone of and nature of the pore spaces in the soil or saturation results. This is ground water and rock. Water stored below the water table is the top of the saturated zone is the ground- the source of supply for springs and wells. water table, or simply, the water table (fig. 35). If the water table intersects the land surface, The depth of the water table beneath the sur- as it may on the sides of valleys, the water face varies according to topography, structure will flow or seep out as gravity springs or seeps. 69 Figure S5. Water sources. c. Springs and Seeps. Subsurface water acting under the influence of pressure issuing at the surface as a spring has a distinct from a higher water level is forced current, flowing continuously or intermittently to the surface of the ground. Fissures from a localized area. Water issuing as a seep in the rock, fault zones, and, in some emerges slowly over a large area, without a cases, solution channels may serve as noticeable current. Springs and seeps are of avenues along which water can move two principal kinds: gravity and artesian. to the surface. The water is generally (1) Gravity springs. Gravity springs and under much hydrostatic pressure, and seeps are those in which the subsur- therefore rises in the spring. Because face water flows by gravity from a of this rise, the spring or well is higher point of intake to lower point classified as artesian. A well with of issue. This may occur where the enough pressure to bring the water water table comes near or intersects above ground is called a flowing ar- the surface of the ground, usually tesian well. If the water rises only to around the margins of depressions, an intermediate level, it is a nonflow- along the slopes of valleys, and at the ing artesian well. foot of alluvial fans. Another type d. Circulation. Ground water is not static occurs along an exposed contact be- but moves slowly through openings in the rock tween the overlying pervious stratum and soil toward points of discharge. The rate and an underlying impervious of movement is controlled by gravity or hydro- stratum. They may appear at almost static pressure (the pressure exerted by water any elevation aiong a slope. at a higher level) and by the capacity of the (2) Artesian springs. Artesian springs rock or soil to transmit water, termed its occur where confined subsurface water permeability. Climate governs the amount of

70 water that will be contributed to the surface. its width, depth, and velocity. Rivers more than The amount that will be absorbed depends upon 150 meters (500 feet) in width are major the amount of pore space, or the porosity of obstacles. the ground. c. River Floods. Floods may cause long traffic interruptions particularly by damaging 68. Hydrological Effects on Military temporary bridges. A flood may immobilize a Operations theater of operations unless an adequate system of stream-gaging stations and flood-warning a. Rivers. Wide, deep rivers with valleys agencies has been established for all key rivers. that offer concealment may provide good de- Streams in mountainous areas are characterized fensive areas. The employment of a river as a by a high velocity with considerable variation forward edge of battle area (FEBA), however, in their flow. While they may be effective may also result in a frontage too wide for obstacles during flood periods, they usually are effective defense and with many covered areas so low in dry seasons that their beds may offer that interfere with observation and fields of routes of approach rather than obstacles to fire. Marshy terrain and ditches or tributaries movement. Such streams, however, are likely interfere with lateral communications and the to have beds so rocky as to eliminate vehicular movement of reserves. movement. b. River Line. In the attack of a river line, d. Lakes. Usually lakes are obstacles to the initial objectives are key terrain features movement because few are narrow enough to that could permit the enemy to bring effective be bridged. They must be bypassed or crossed small-arms fire on the crossing area. Next are in amphibious vehicles or boats and where they features that allow the enemy to deliver ob- exist in chains or large groups, as in glaciated served artillery fire, and, finally, those areas areas, they become major obstacles (fig. 36). on the enemy side of the river that are required The narrow land corridors separating the lakes to accommodate the troops, equipment, and canalize troop movements and limit maneuver, installations necessary to prevent the enemy rendering troops highly vulnerable to attack. from delivering effective sustained artillery A series of interconnected lakes may provide fire. A river or stream may be a temporary an extensive communication system and may obstacle to cross-country movement, but it slows also include navigable rivers and canals as in down advancing forces only until it is bridged Finland. An ice cover that is 1 meter (3 feet) or assault boats can be brought to the site or or more in thickness will support heavy loads. a crossing by helicopter is effected. The effec- Roads across frozen lakes may be prepared by tiveness of a river as an obstacle increases with clearing away the snow.

Figure s6. Arctic lake region (Northwest Canada). 71 e. Marches and Swamps. Normally movement bacterial pollution, seasonal varia- through a swamp or marsh is usually limited tions). to causeways, but many vehicles are now used (6) Bank characteristics (composition, in swamps in what is known as a riverine stability, height, and slope). operation. These may be key terrain features (7) Regulatory structures (levees and that could be seized by airborne, airmobile, dams). or mechanized forces prior to a large-scale movement. Mud and peat bottoms usually pre- (8) Islands, bars, shoals, and rapids vent cross-country movement. Special engineer (name, size, surface roughness, eleva- floating and portable bridging equipment may tion, and pattern). be necessary to supplement other means of (9) Ice (earliest, latest, and mean freezing traversing a swampy area or to cross or bypass and breakup dates, extent of frozen a gap in a causeway. Snow roads may be built surface; thickness of ice; carrying over swamps by removing the snow and then capacity; and frequency and location pouring water over the cleared surface until of ice jams). a frozen surface is obtained. (10) Kind and prevalence of animal and vegetable life. 69. Information Requirements - Drainage (11) Type and location of crossings. Major drainage areas are shown on maps of appropriate size accompanying some terrain (12) Utilization of watercourse (for water studies. Textual notes are provided if the im- supply, irrigation, disposal of waste). portant facts cannot be shown adequately on (13) Accessibility for military water sup- a map. Detailed information on features of ply (relation of road nets to potential military significance along a stream or portions water points, off-road approaches, in- of it may be shown on a strip map or annotated take problems). photomosaic. Information may include- b. Lakes. a. Rivers and Streams. (1) Name or other identification, and (1) Name or other identification, and location. location. (2) Length, width, depth and surface (2) Channel characteristics (form (fig. area at low, high, and mean water; 37), length, profile, gradient of stream periods of occurrence of each. bed). (3) Gage locations and periods of record, (3) Bottom characteristics (composition, zero gage elevations, mean and ex- depth, firmness, unusual conditions). treme gage heights and periods of occurrence. (4) Flow characteristics. (4) Shore characteristics (composition, (a) Measurements and periods of oc- stability, height, and slope). currence at low, high, and mean (5) Physical and chemical characteristics water of depth, width, volume of of water (turbidity, color, odor, taste, discharge, and velocity (minimum, temperature, chemical composition, maximum, and mean). bacterial pollution, seasonal varia- (b) Special phenomena (crosscurrents, tion). undertows, eddies, floods) ; periods; (6) Bottom characteristics (composition, area covered; destructive effects. depth, and firmness of material, un- Tidal effects at low, high, and mean usual bottom conditions, profiles). tides. (7) Regulatory structures. (5) Physical and chemical characteristics (8) Islands, bars, and shoals (name, size, of water (turbidity, color, odor, taste, surface roughness, elevation, and temperature, chemical composition, pattern). 72 I *r

Figure 37. Characteristic braided stream drainage pattern (Canada). (9) Ice (earliest, latest and mean freezing water points, off-road approaches in- and breakup dates; extent of frozen take problems). surface; type and thickness of ice; c. Marshes and Swamps. and carrying capacity). (1) Information in b above, as applicable. (10) Kind and prevalence of animal and (2) Seasonal variations (months when vegetable life. variations in extent and wetness are (11) Type and location of crossings. greatest and least). (3) Cross-country movement under vari- (12) Utilization of water body (for water ous seasonal conditions. supply, irrigation, disposal of waste). (4) Existing or potential causeways. (13) Accessibility for military water sup- (5) Special conditions (quicksand, per- ply (relation of road nets to potential mafrost).

Section IV. NEARSHORE OCEANOGRAPHY 70. Beaches and where there is an abundant supply of a. Description. A beach is defined as the material deposited by streams. Along hard-rock area extending from the shoreline inland to a coasts and on those not well supplied with marked change in physiographic form or ma- stream-carried material, beaches are short and terial, or to the line of permanent vegetation discontinuous, and are usually separated by (coastline). In amphibious operations, it is bold headlands or rock outcrops (fig. 38). considered that portion of the shoreline desig- b. Width. The width of a beach is subject nated for landing a tactical organization. to considerable change. Where there are sea- Beaches are characterized according to their sonal variations in wave attack and the supply predominant surface material, such as sand, of material, beaches may disappear or be great- silt, cobble, pebble, boulder, or by combinations ly damaged when the wave attack is heaviest. of these materials, such as sand and pebble. Beaches formed principally by streams usually Mud beaches are common, but silt is not usually show marked seasonal variations in width, and found in beach form, occurring more commonly are widest during the period of least rainfall. in underwater banks and shoals. In general, Beach widths are most nearly constant when beaches are long and continuous on low-lying the beaches are protected by groins or similar coasts, or on shores with soft rock formations, structures.

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74 c. Slope. The slope of a beach is determined g. Fresh Water. Fresh water is seldom chiefly by the size of the beach material and available on undeveloped beaches, although it the intensity of wave attack. Beaches of fine may be obtained from nearby streams or in sand that are not subject to intense wave action completely inclosed pools or lagoons that lie commonly have slopes ranging from 1 on 5 to immediately behind the beach. Streams or 1 on 60. Coarse material under light wave rivers with steep gradients that cross the beach attack results in beach slopes from 1 on 5 to will provide fresh water at sites above the 1 on 10. The band of wave uprush on a beach highest reach of the tide. is a good indication of the slope. On air photographs it may appear as a dark band lying 71. Terrain Adjacent to Beaches just landward of the waterline. A wide uprush a. Ridges. Beach ridges are mounds of beach band indicates a flatter slope than a narrow material heaped up by wave action along the band. On gravel beaches, however, uprush upper limit of wave uprush as single ridges bands are always narrow, and usually do not or as a series of approximately parallel ridges appear clearly on aerial photographs. extending some distance inland. Commonly d. Firmness. There is a wide variation in these ridges reach from 1 to 2.5 meters (3 to firmness between different beaches and differ- 8 feet) above mean high tide, but individual ent parts of the same beach. Beaches are most ridges may be as high as 9 meters (30 feet). firm when damp and when the material size is High ridges are found only in exposed locations, small. Dry sand usually is soft, except when the and are signs of occasionally severe storm wave material size is small. Pebble, cobble, and action. Ridges occur only when there is an boulder beaches are firm as far as bearing abundant supply of material on or in back of strength is concerned but are loose, making it the beach. In some locations belts of beach difficult for tracked vehicles to cross them. ridges extend for 2 or 3 kilometers (a mile or Silt and clay are invariably soft, but combina- two) inland, with a vertical difference in ele- tions of mud and sand provide a hard surface. vation of only a meter (few feet). Usually these As a rule, exposed beaches are firmer than areas are covered with grass or low bushes. similar beaches in sheltered locations. b. Dunes. Dunes are formed by windblown e. Vegetation. Vegetation immediately in rear sand carried inland from the beach and depos- of a beach is an indication of stability. Such ited as irregular hills or mounds. The sand is of areas are firmer than other parts of the beach fine to medium size. Dunes may reach heights and always lie above the limit of wave uprush. of 90 meters (300 feet), although commonly There is no vegetation on gravel beaches, but they do not exceed 30 meters (100 feet) in beaches composed of gravel and sand in com- height. Where there is vegetation, low bushes, bination may have a vegetation cover. and grass the dunes are fairly firm and can be f. Assault Landing. Assault landing is based crossed by light vehicles. Fresh water may be upon the potential of the beach and hinterland obtained from wells sunk in depression be- to permit the initial landing and the logistical tween dunes (fig. 39). support for the operation. Attack transport ships (APA) and attack cargo ships (AKA), 72. Underwater Topography which have a loaded draft of 8 meters (27 ft) a. Description. An examination of the terrain and 7.3 meters (24 ft), respectively, require as shown in photographs, topographic maps, landing crafts for unloading. A landing ship and hydrographic charts will indicate the prob- tank (LST) requires a maximum draft of 4 able characteristics of the hydrography. If the meters (13 ft), a landing craft medium (LCM) land behind the beach is flat and sandy or 1.5 meters (5 ft), and a landing craft, utility marshy, the sea bottom close inshore also will (LCU) 2 meters (6.5 ft). Additional aid in be fairly flat. A beach located on a long landing supplies and personnel include mobile stretch of regular coastline normally will have pier sites such as the Spud Barge pier, bridging one or more sandbars offshore. Large rock out- and engineer equipment required to prepare crops along the beach or close inland indicate the terrain for landing. that there are probably similar outcrops under- 75 - - .- TRANSVERSE

LONGITUDINAL

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Figure 39. Windblown stationary dunes. water near the shore. Beaches backed by cliffs entire beach profile is changeable, varying with or steeply rising hills generally will have a the wave conditions that act upon it. Short fairly steep underwater gradient. The form of concave or pocket beaches (fig. 40) flanked by the beach also indicates the underwater con- well-developed headlands are the most constant tours. A wide, flat beach is an indication of a in their form. gently sloping bottom offshore, and a sharp b. Bottoms. The characteristics of the mate- narrow beach suggests a steep slope. Sand rials that comprise the nearshore bottom are beaches have flat to steep slopes, and beaches of significant in relation to their suitability for gravel, cobble, or boulders are usually steep. the movement of men, vehicles, and landing It must be remembered, however, that the craft. Bearing strength and smoothness of grad-

76 -- _ I~X

Figure 40. Concave beach. uations are the most important factors. Sand, open growth of branching corals. Reef corals sand and shell, and gravel bottoms are ideal cannot stand exposure to the air for more than for landing operations. They are firm and a few hours, so that their upward growth is usually quite smooth, although bank, bar, and limited by the level of mean low water. They shoal formations are common. Sand and mud belong to one of three types-fringing reefs, mixtures may be either firm or soft, but they barrier reefs, or atoll reefs (fig. 41). usually are smooth. Mixtures with a high per- b. Fringing. A fringing reef is attached to centage of sand are firm, the firmness decreas- the shore. If the wave attack is weak, there ing as the sand content is reduced. This type of will be a gently sloping beach of coral sand. bottom often has soft spots that may prove Strong wave attack results in steep gravel, hazardous. Mud bottoms are generally avoided, cobble, and boulder beaches. On most fringing since they are soft, smooth, and slippery. An reefs there are boat channels about 0.3 to 4.5 exception is the case of a thin mud cover over- meters (1 to 15 feet) deeper than the rest of lying a rock bottom, where the rock provides the reef-flat, from 10 to 45 meters (10 to 50 an underlying formation that will give a yards) or more wide, and more than a mile satisfactory bearing surface if the mud is not in length. These run approximately parallel to more than a meter thick. Clay bottoms are the land, opening into breaks in the reef, and unsatisfactory, since they are soft and slippery providing convenient waterways for small and have little strength. craft. 73. Coral Reefs c. Barriers. Barrier reefs are located a. Description. Reef-building corals are ma- roughly parallel to the coastline at some dis- rine animals that remove lime from sea water tance offshore. Whether or not a craft can and deposit it around their living bodies, cross a barrier reef depends upon the depth making hard structures of many types. They of the coral below water. Usually the coral do not flourish at temperatures much under surface is about 15 centimeters (6 inches) 75 ° F. Consequently coral reefs are found only above mean low water, but it may be deeper. in tropical waters. Since corals cannot move, Walking upon the reef is dangerous, since securing microscopic food from water moving the reef-flat is seldom above water and the around them, they are usually found near the holes between coral colonies are irregularly edge of reefs, along channels, and out from spaced, deep, and lined by jagged coral. At low headlands. They cannot form opposite muddy water, extensions of the reef into the lagoon streams or those with a heavy discharge. If behind it may create compartments that hinder the water movement in coral areas is swift or prevent the free movement of craft along enough, rounded coral heads will predominate, the reef. and in more quiet water there usually is an d. Atoll. Atoll reefs (fig. 42) are more or 77 Figure 41. Barrier and fringing reefs--diagrammatic cross-sections. (A) Wide barrier reef. (B) Narrow exposed fringing reef. (C) Protected fringing reef. (Not drawn to scale.) less rings of coral inclosing circular lagoons. the viewpoint of landing operations, the most The marginal zone of the reef is a strip from unfavorable feature is the high, surf-covered 25 to 70 meters (25 to 75 yards) wide, across marginal zone. Surf intensity is less on the which a belt of surf moves with the rise and leeward side. On the lagoon side by entering fall of the tide. If the outer, seaward slope of through channels or breaks in the reef, craft the reef is steep, there is a clear approach for may land on the sand beach at high water. landing craft. A gentle slope will have coral Crossing the reef-flat at low tide is impracti- heads growing just outside, making an ap- cable. proach dangerous. At high tide it may be possible to cross the marginal zone by boat. Reef 74. Military Considerations islands usually are located on higher parts of an atoll reef. Typically these islands are surround- a. Coastlines. A concave coastline is formed ed or partly surrounded by a beach 3 to 15 by a projection of water (bay or gulf) extend- meters (10 to 50 feet) or more wide, consisting ing into the coast. From the flanks, converging of coral sand and organic debris. Reef islands fires may be brought upon landing forces. The are seldom more than 3 to 4.5 meters (10 to 15 convex type of shoreline includes gently out- feet) higher than the reef-flat, and their in- curving shores, points, capes, and peninsulas. teriors usually are flat and featureless. From Supporting fires may be placed on the defender

78 Figure 42. Atoll reefs--diagrammatic cross section. (A) Open reef area. (B) Area of impermanent debris accumulation. (C) Reef-island area. (Not drawn to scale.) from his flanks and, occasionally, from his rear. normally with a rough tablelike surface, that His routes of withdrawal or reinforcement are extends seaward from the shoreline at a level restricted. It is difficult for the defender to slightly above or below the water. A wide organize his fires and to secure extensive fields fringing reef provides an area well suited to of fire. Convex shorelines are more exposed to the organization of defensive smallarms fires. currents, winds, and surf and are often steep and rocky, making landing difficult. A straight c. Offshore Islands. Frequently shorelines shoreline has no prominent indentations or are protected by groups of small islands lying promontories. It offers no decisive advantage so close to the mainland that they form a com- either in attack or defense. Very few coast- plicated system of waterways immediately off- lines, however, are so straight that provide shore. Routes of approach to the mainland no positions for flanking fires. An irregular through the islands may be tortuous and re- coastline is a complex of concave and convex stricted, making an approaching landing force shorelines. highly vulnerable throughout its shoreward movement. These islands may be neutralized b. Reefs. Barrier and atoll reefs may be with nuclear weapons or may be isolated and obstacles at a distance from tlhe landing beach. reduced in detail by successive minor landings A fringing reef forms a nearshore obstacle, preceding the main amphibious attack. Once

79 secured, they provide the attacker with favor- tidal heights and surf, local peculiar- able artillery positions to support the landing. ities). (5) Waves and surf (height and period 75. Information Requirements - Landing of offshore waves; intensity). Areas c. 'Beach.' Terrain studies made for planning amphibious operations are very detailed. Normally (1) Material (type and size, firmness, they are based upon the complete data that is variability with weather or season, provided by special studies and major sources. subsurface material). In general, the following items represent the (2) Gradient (note particularly scarps fundamental information requirements relative and ledges). to a proposed landing area: (3) Beach structures (groins, bulkheads, a. Location. jetties, submerged remains of former structures). (1) For a beach 3 kilometers (2 miles) or more in length, the latitude and longi- (4) Rivers and streams (variability in tude of its limits; for a beach less beach character where rivers cross than 3 kilometers (2 miles) long, the beach; river channels). center of the landing area is given. (5) Effects of weather and duration of (2) Nearness to objective of the opera- darkness and daylight. tions, if known, and to developed areas (6) Local use of beach. such as water terminals, harbors, and (7) Sources of fresh water on or near adjacent beaches. beach (both potable and nonpotable). b. Sea Approach. d. Terrain Inland or on Flanks. (1) Landmarks, both natural and man- (1) Topography (topographic features, made. waterways, swamps or marshes, vege- (2) Hydrography (nearshore and offshore tation, location and size of possible depths; flats (tidal or other), charac- dump or assembly areas). ter of the material and its bearing (2) Exits (existing exits by roads or strength; length of and depths over trails; cross-country exits; roads, with reefs, bars, shoals, or other natural details of width, surface, construction; obstructions; anchorage areas and railways, tramways). their conditions; character of near- (3) Aircraft landing sites within a 16- to shore bottom material). 24-kilometer (10- to 15-mile) dis- (3) Tides and currents (tidal rise and tance from beach (dimensions, sur- fall, local peculiarities, direction and face, topography). magnitudes of currents; neaps and (4) Utilities (communications, electricity, springs). water supply, transportation). (4) Winds (strength, direction, effect on (5) Helicopter landing sites.

Section V. SURFACE MATERIALS 76. Types of Soils tion about soils, their engineering properties, a. Composition. Soil is defined as the uncon- and testing techniques is contained in TM solidated material that overlies bedrock. Soil 5-541. Some essentials of soils trafficability is made of disintegrated rock, in the form of are given in chapter 9. For field identification sand or clay, and humus, the disintegrated and classification, soils may be grouped into remains of past vegetation. Detailed informa- five principal types: gravel, sand, silt, clay, 80 and organic matter. These types seldom exist vary from lean clays (low plasticity) to fat separately but are found in mixtures of various clays (high plasticity). Many clays which are proportions, each type contributing its charac- brittle or stiff in their undisturbed state be- teristics to the mixture. come soft and plastic upon being worked. b. Gravel. Gravel consists of angular to 77. Soil Maps rounded, bulky mineral particles ranging in size from about 0.6 to 8 centimeters (1/4 inch to a. Contents. Soil maps or overlays indicate 3 inches) in diameter. It is classified as coarse the predominant soils in given areas, identify- or fine; well or poorly graded; and angular, ing them according to their engineering char- flat, or rounded. Next to solid bedrock, well- acteristics. Such maps may be constructed from graded and compacted gravel is the most stable air photographs or ground reconnaissance or natural foundation material. Gravel is easy to made from existing soil and geologic maps and drain, easy to compact when well graded, af- reports with the classifications expressed in fected little by moisture, and not subject to engineering terms. Agricultural soil maps can frost action. be large enough to provide detail for tactical planning, but often the designated soil type c. Sand. Sand consists of mineral grains applies only to the surface soil. These maps ranging from about 6 millimeters (1/4 inch) should indicate the following properties of down to about 0.08 millimeters (.003 inch) in soils: diameter. It is classified according to size and (1) Permeability. gradation as coarse, medium, or fine; and as being angular or rounded. Well-graded angular (2) Stability under stress. sand is desirable for concrete aggregate and (3) Bearing capacity. for foundation material. It is easy to drain, (4) Important variations of (2) and (3) little affected by moisture, and ordinarily not above with changing moisture con- by frost action. Sand provides an excellent road tent. subgrade material when it is confined. Care is required, however, to distinguish between a fine b. Coverage. For strategical planning, soil sand and silt. maps should cover the area of the study. A large amount of general information may be d. Silt. Silt consists of natural mineral grains presented, because detailed plans may not be ranging from about 0.08 millimeters (.603 firm and the future weather conditions uncer- inch) to about .005 millimeters (.0002 inch) tain. The information includes the effects of in diameter. It lacks plasticity and possesses weather upon the soils. The reliability of the little or no cohesion when dry. The term information must be clearly indicated. rock flour is commonly used to describe inorganic silts of glacial origin. All silts are e. Planning. Soil maps for tactical planning treacherous for trafficability and as a founda- cover a smaller area than do strategical soil tion material. Because of its inherent insta- maps. They are of a larger scale and contain bility, slight disturbances in the presence of more precise, detailed information. Greater ac- water, such as traffic vibrations transmitted to curacy is possible because more details are a wet silt subgrade, will cause the silt to be- known about the proposed operations. Recon- come soft or to change to a "quick" condition. naissance and patrol reports make it possible When ground water or seepage is present, to check the ground, and weather forecasts are silts exposed to frost action are subject to in- available to indicate what the prevailing tensive ice accumulation and consequent heav- weather will be. The information contained on ing. Silts are difficult to compact and drain. such maps is useful in determining- e. Clay. Clay generally consists of particles (1) Areas critical to cross-country move- smaller than 0.005 millimeters (.0002 inch), ment as they affect both advances and microscopic in size. Its plasticity and adhesive- counterattacks. ness are outstanding characteristics. Depending (2) Stretches of road liable to failure upon the proportion of coarser grains, clays under heavy traffic. 81 (3) Suitable and unsuitable areas for air- sand is an obstacle to vehicles, particularly on fields, field fortifications, and other slopes. installations. d. Silt. When dry, silt provides excellent traf- (4) Areas with soil conditions that are ficability, although it is very dusty. Silt ab- unsuitable for tank and vehicle parks. sorbs water quickly and turns to a deep, soft (5) Difficult areas for field and air de- mud when wet, imposing a definite obstacle fense artillery deployment. to movement. It dries quickly after a rain, soon becoming trafficable again. (6) River bank conditions for bridge foundations and crossing operations. e. Clay. When thoroughly dry, clay provides d. Rear Areas. In planning rear area ac- a hard surface with excellent trafficability, but tivities, soil maps are useful for determining it is seldom dry except in arid climates. Al- road conditions. In order to stand up under though clay absorbs water very slowly during heavy traffic during periods of frost and thaw, a rain, it also takes a long time to dry. Wet a road must have a well-drained subsoil foun- clay is very sticky and slippery. Slopes with a dation. A knowledge of the soils in an area clay surface are difficult or impassable, and will reveal which stretches of road will be most deep ruts form rapidly on level ground. A susceptible to breakdown during a thaw, pro- combination of silt and clay makes a particu- viding a guide to selecting the best supply larly poor surface when wet. routes and indicating portions of the road f. Special Soil Conditions. If a soil has un- where precautions must be observed. When derlying bedrock near the surface, it will be- supplemented by an aerial reconnaissance, soil come thoroughly saturated after a rain. The maps are a valuable aid in highway location water cannot drain away, making the surface and relocation. They indicate the soil areas untrafficable. with desirable or undesirable engineering characteristics and also show the nearest sources g. Manmade Effects. Soil under cultivation of materials for road construction and mainte- because it has been worked is softer and ab- nance. The information about soil conditions sorbs water more quickly than other soils and given by a soil map is invaluable in selecting may therefore have poorer trafficability. Usu- sites for airfields, storage installations, ammu- ally the presence of irrigation structures indi- nition dumps, and vehicle parks. Preliminary cates that the soil is soft and contains water study of the map prevents unnecessary field and the soil generally will have poor traffica- reconnaissance. bility. The types of crops cultivated in an area provide indications as to the nature of the soil. 78. Military Aspects of Soils Since gravelly soils are especially suitable for a. Weather. The actual identity of the type fruit orchards, for example, the presence of of soil in any area is of little practical value extensive orchards, especially on flat areas, unless the soil is also evaluated in relation to may indicate that the soil has a high gravel the existing or predicted weather. In general, content. Many cultivated plants have specific the major soil types have the following charac- soil and water requirements, giving a clue to teristics: the soil and drainage of the area. b. Gravel. Weather has little or no effect on h. Nuclear Weapons. Soil composition and the trafficability of a gravel soil which is ex- density affect the amount of damage by shock cellent for tracked vehicles. It it is not mixed that will result from a surface or subsurface with other soil, however, the loose particles burst. Propagation of the shock wave is poorest may roll under pressure, hampering the move- in light, loamy soils and best in plastic, wet ment of wheeled vehicles. clay. The pressures transmitted by the blast may be 50 times greater than those trans- c. Sand. When wet enough to become com- mitted through sandy clay. The size and shapes pacted, or when mixed with clay, sand gives of craters produced by a surface or subsurface excellent trafficability. Very dry, soft, or loose burst, their effectiveness as obstacles and the 82 intensity and decay rate of induced radiation to transportation and power facilities. Plains, in the soil are also affected by the soil com- terraces, and alluvial fans usually are best for position and density. bunker type installations. The most favorable terrain for tunnels normally is found on 79. Information Requirements-Soils plateaus, escarpments, high hills, and moun- In a terrain study, soil information usually tains with steep bare-rock surfaces. Large is presented in tabular form, with the data bunkers require deep, well-drained soils, with keyed to a soil map or overlay. It covers-- the water table at least 4.5 to 6 meters (15 to 20 feet) below the surface. They should be a. Extent of each dominant soil type. protected against surface-water flooding, espe- b. Depth of each type in areas indicated. cially if they are located on low plains. Military tunnels may be constructed for tactical, com- c. Surface texture (fine or coarse). munication, storage, and shelter purposes, d. Parent material. including- e. Description of material. (1) Undermining of enemy positions and countermining. f. Properties when wet, dry, or frozen, in- (2) Galleries for water cluding suitability for specified military supply. vehicles under various conditions, bearing (3) Fortifications (headquarters, gun em- capacity for structure foundations, and perme- placement, ammunition storage, de- ability when wet. fensive installations). g. Variations from dominant soil type in (4) Underground factories and hangars. specified areas. e. Tunneling. h. Areas of permafrost, permanent ice and (1) Construction. Before tunneling oper- snow. ations are initiated, a geologist should i. Seasonal state of the ground (dry, wet, evaluate the proposed site. Tunnel flooded, frozen, snowcovered) by seasons, type installations are favored by high, months, or shorter periods. Effects of each steep slopes of exposed bedrock. The state on cross-country movement, construction, tunnel is kept dry by placing the excavation, cover and concealment, and other lowest levels above the water table military aspects. and by constructing it in rocks that have a minimum of fissures, joints, 80. Rock and faults that would permit seepage and flooding. The size of the chambers a. Classification. Rock may be defined as the depends upon the stability of the rock. firm and coherent or consolidated material of The thickness of natural cover re- the earth's crust. Bedrock is solid undisturbed quired to give adequate protection rock either exposed at the surface or underly- depends upon the type of rock and ing the soil. Igneous rock is formed by cooling soil, degree of soundness of the rock, and solidification from a molten or partly absence of joints and fissures, and the molten state; sedimentary rock, from material size and shape of the underground accumulated as a deposit from water or the air, openings. and metamorphic rock, by the recrystallization of igneous or sedimentary rock under the in- (2) New methods. In Viet Nam extensive fluence of heat, pressure, or both. The informa- hand-dug tunnels and tunnel com- tion, characteristics, and uses of rock are ex- plexes have been found. They are plained in TM 5-545. usedeas hiding places, caches for food and weapons, headquarters, and pro- b. Underground Installations. Underground tection against air attack and artil- installations require rock and soil that are lery fire. They have concealed en- easily worked and locations that are accessible trances and exits, camouflaged bunk- 83 ers, trap doors, and dead ends to that will be required depends upon the purpose confuse the attacker. One trap door of the study. Requirements may include- may lead to a short change-of-direction tunnel and another door to a a. Rock Deposits. second change of direction, and a (1) Location and extent of deposit. third door to the main tunnel. There (2) Type and properties of the material. are also multilevel complexes with storage and hiding rooms at lower (3) Suitability for construction use (as levels. Some of these have air or water aggregate, binder, surfacing, ballast, locks as "firewalls" to prevent blast, riprap, masonry construction mate- fragments, gas or smoke from passing rial). from one section to another. The en- (4)Accessibility. trances are camouflaged and booby- trapped. b. Underground Shelters. (1) Existing areas (mines, caves, under- 81. Information Requirements-Rock ground manmade installations). Char- Terrain studies of an area will be concerned acteristics. Special constructions. chiefly with the availability of unexploited (2) Areas suitable for development (rock natural deposits suitable for the construction structure, comparative advantages of roads, protective works, airfields, and under- and disadvantages of indicated loca- ground shelters. The particular information tions).

Section VI. VEGETATION

82. Broad Classification of Plants a serious obstacle to free passage is classified as woods or brushwood. Commonly, a deep Vegetation may be classified in four broad woods is considered as one that is large enough categories-trees, shrubs, grasses, and cultivated vegetation. The type of vegetation in an to provide ample concealed maneuver space for area gives an indication of the climatic condi- large units deployed in depth. This would in- tions, soil type, drainage, and water supply. clude a woods that would conceal both the assault and reserve echelons of a brigade in the Seasonal seepage or a rise in the ground-water supply often is indicated by vegetation such attack. A shallow woods is one that is not large enough to conceal elements of this size. as reeds, sedges, cottonwoods, and willows, Dense woods are those where the growth is which thrive wherever seepage occurs. Simi- larly, arid conditions are also indicated by thick enough to interfere with visibility suf- characteristic desert vegetation. TM 5-545 de- ficiently to limit the maneuver of troops. scribes the indications typical of various plant b. Characteristics. In temperate regions, species. trees are commonly found at elevations of not more than 2,440 meters (8,000 feet) above sea 83. Trees level. A good forest climate is one with a warm, rainy vegetative season, a continually moist a. Definitions. Trees are defined as perennial subsoil, and low wind velocity. The growth of woody plants at least 10 feet in height, with trees is greatly influenced by the temperature single stems and definite crown shapes, A of the air and soil; even the hardiest conifers forest is an extensive area covered by trees require a mean warm month temperature of at growing in a close formation, so close that in least 50° F. most cases their crowns touch. Smaller areas covered by trees may be termed woods, groves, c. Classification.Trees are classified as either or woodlots. In the terminology used on U.S. deciduous or evergreen (fig. 43). Deciduous Army maps, any perennial vegetation high trees drop all their leaves seasonally, but ever- enough to conceal troops or thick enough to be green trees retain their leaves throughout the 84 year. Trees are also either needleleaf or broad- the year. Almost all deciduous forests are lo- leaf. In the middle latitudes, needleleaf trees cated in the Northern Hemisphere. The impor- are predominantly evergreen, and broadleaf tant dimensions of trees in a wooded area are trees are predominantly deciduous. In the hu- the diameter of the tree stems at breast height, mid tropic, nearly all trees are evergreen' be- the average height of the trees, and the average cause the climate remains uniform throughout height above ground of the lowest branches.

Figure 4A. Mixed vegetation, showing (a) evergreen trees, (b) deciduous trees, (c) brush, and (d) sedges (Northern Manitoba).

84. Low-Latitude Forests Typical jungle conditions, with thick and impenetrable undergrowth, are characteristic In the low latitudes, tropical rain forests, chiefly of sections where light reaches the forest the princi- swamp forests, and moss forests are floor, as one precipitous wet slopes, along rivers pal types. and coasts, and in abandoned agricultural a. Tropical Rain. In the tropics, rain forests clearings. (selva) blanket many square miles of moist b. Tropical Swamp (fig. 44). This forest low lands in regions where rainfall is heavy occurs in low terrain near or in swampy re- and well distributed throughout the year, with gions. Mangrove swamp forests (fig. 45) cover no marked dry season. The Amazon Basin and large areas along tropical salt-water coasts, West Central Africa are the two largest areas presenting an almost impenetrable barrier to of tropical rain forest, although it is also found movement. This type of forest is found in the tropical along many rainy coasts and on soft mud around river mouths, deltas, and in- islands. This type of forest covers more than lets, along shallow bays on small islands, and one-tenth of the earth's total land surface and upstream as far as the tidal influence is felt. comprises nearly one-half of the total forest Mangrove forests include several kinds of trees, areas of the world. The rain forest consists of all with thick buttressed roots that extend as broadleaf trees of many species that form a high as 3 meters (10 feet) above the ground. canopy thick enough to shut off most sunlight. These spread outward becoming interlaced in The trees are commonly from 30 to 45 meters a network that makes movement by foot almost large diame- (100 to 150 feet) in heights, with impossible and prohibits any type of vehicular lower branches. ters, smooth trunks, and few Nipa palms, which generally grow Lianas, rope-like plants that entwine them- movement. in or near mangrove swamps, also present selves around trunks and branches, are common. Usually the undergrowth is not dense, al- almost impassable barriers (fig. 46). though it restricts observation. In the deepest c. Moss. This forest is found in the higher shade, there is usually only a thick mat of ferns latitudes just above the rain forest areas, or herbs that offers no obstacle to movement. chiefly at altitudes of 915 meters (3,000 feet) 85 or higher on the tops of tropical mountains that conceals the earth. This moss often covers wherever high humidity and cloudiness are chasms and ravines, making them appear to persistent. The trees are small with long over- be level terrain. The moss forest accordingly is hanging branches. Moss grows on the branches, hazardous to movement. It is dark and gloomy tree trunks, and ground, where it is intermin- and so dense that very little sunlight penetrates gled with ferns and vines to form a blanket the canopy. Visibility is extremely limited.

i"-~~~~~41

Figure 44. Swamp forest (air view) (Sanibel National Wildlife Refuge, Florida).

Figure 45. Mangrove swamp (Malay Peninsula). 85. Middle-Latitude Forests broadleaf evergreen trees adapted to regions with long, hot periods of summer a. Types. The principal forest types in the drought. They middle latitudes include Mediterranean scrub are found in the borderlands of the Mediter- forests, broadleaf forests, and needleleaf ranean Sea, as well as in California, Chile, forests. southern Australia, and the Capetown region of Africa. These areas are subtropical, with b. Mediterranean Scrub. These consist of mild, rainy winters and long, dry, hot sum- 86 Figure 46. Nipa palms (Northern New Guinea). mers. This type of forest consists of low trees clusively evergreen. The growth and discard of and woody shrubs. Where climate and soil the needles is a continuous process not confined conditions are most favorable, the virgin to any particular period or season. Usually the forest is composed of low, widely spaced trees needleleaf forests occupy the colder continental with massive trunks and gnarled branches. Be- locations on the poleward side of the broadleaf tween the trees the ground is completely or forests. In areas of poor sandy soils, or on partially covered by a pale, dusty bush and steep mountain slopes where soils are thin or shrub vegetation resembling the soil in color. rocky and temperatures are lower, needleleaf Cork oaks and olive trees are typical of this trees may supplant broadleaf trees even in the type of forest. middle latitudes. South of the great belts of subarctic needleleaf trees there are large areas c. Broadleaf. Most of the temperate broad- of needleleaf trees that provide valuable timber leaf forest is composed of deciduous trees with such as the forests of the Pacific Coast, western a seasonal leaf fall, such as oak, hickory, maple, Canada, and Alaska. The southern pine forests ash, elm, walnut, beech, and poplar. Along the in the Atlantic and Gulf Coastal Plains of the humid subtropical margins of the middle lati- United States also are major sources of tudes, principally in southern Japan, New timber. Zealand, and southeastern Australia, there are evergreen broadleaf forests that resemble rain 86. High-Latitude Forests forests, with dense undergrowth and heavy vines. Temperate broadleaf forests vary widely A wide belt of needleleaf forests extends in composition, the dominant tree species dif- from coast to coast in the subartic regions fering from one region to another. In some of Eurasia and North America below the tree- areas there are many conifers among them and less tundra regions. This Eurasian forest is the forest may be described as mixed. the largest continuous forest area in the world. Needleleaf trees such as fir, spruce, larch, and d. Needleleaf. Needleleaf trees are almost ex- pine predominate, although in the swamp areas 87 there are some broad leaf trees such as aspen, of middle latitudes. In many arid and semiarid willow, birch, or mountain ash. The area has areas they are the dominant vegetation. They short, cool summers and long, dry, cold winters are prevalent in the subarctic and in large, so that growth is slow, and few trees are more burned-over or cutover areas in humid regions. than 0.45 meter (11/2 feet) in diameter. There b.. Classifications. Shrubs, like trees, are are numerous large swamps and marshes cov- either deciduous or evergreen, needleleaf or ered with moss, and containing such trees as broadleaf. In the middle latitudes, most broad- balsam and spruce. These areas usually rapidly leaf shrubs are deciduous, and all needleleaf become impassable after precipitation or shrubs are evergreen. In the humid tropics, during a thaw. nearly all shrubs are evergreen. Most arid regions of both low and middle latitudes have 87. Shrubs some vegetation, both deciduous and evergreen, a. Description. Shrubs are woody plants although it is sparse (fig. 47). It may consist usually less than 3 meters (10 feet) high with of low bunch grass with widely spaced bushes more than 1 stem. They include a variety of or fleshy, water-storing plants such as the trees that have had their growth stunted be- cacti. Most commonly, the vegetation comprises cause of soil or climatic conditions. Scrub sagebrush and similar scrub growth. Peren- growth includes cactus, stunted shrubs, sage- nial shrubs of the desert areas grow far apart, brush, mesquite, and similar plants found most with considerable areas of bare soil in between frequently in arid or semiarid areas. Shrubs due to the low rainfall. The rate of growth is comprise the undergrowth in the open forests very slow.

Figure 47. Charaoteristicdesert vegetation (Arizona). 88. Grasses of grass. In low latitudes, grasslands often are termed savannas; in middle latitudes, prairies a. Kinds. Grasses include all kinds of non- (tall grass) and steppes (short grass). Grass- woody plants. A grassland is an extensive area lands in wet or poorly drained areas commonly where the natural vegetation consists primarily are called meadows. For terrain intelligence 88 purposes, grass more than (1 meter) 3 feet plants may be numerous. Steppe vegetation de- high is considered tall, and below that height, velops typically in regions that receive less than short. 50 centimeters (20 inches) of rainfall a year, with a hot summer and a cold, dry winter. b. Tropical Grasslands (Savanna). In areas with heavy seasonal rains and a distinct dry 89. Cultivated Vegetation season, the grasslands or savanna are composed mostly of tall, very coarse grasses that grow a. Field Crops. Field crops constitute the pre- in tufts separated by intervals of bare soil. If dominant class of cultivated vegetation. Vine there are trees, they usually are species that crops and orchards are common but not wide- can withstand seasonal drought and they grow spread, and tree plantations are found only in mostly in clumps in the grasslands or along relatively few areas. The size of cultivated the margins of streams. Savanna grass grows areas ranges from paddy fields covering a rapidly at the beginning of the rainy season, quarter of an acre to vast wheat fields. In a reaching heights of 1 to 3.5 meters (4 to 12 densely populated area, where all arable land feet) in a few months. When dry, the blades is cultivated, each parcel will be used for the become brown, stiff, and harsh in texture, burn- crop that brings the highest yield, making it ing very readily. The grasses usually diminish possible to predict the nature of the soils from in height with decrease in the annual rainfall, information about the predominant crops. and trees become fewer until under semiarid Rice, for example, requires fine-textured soils. conditions nearly treeless steppes, composed of Other crops generally must have firm, well- shorter grasses, are prevalent. Low-latitude drained land. savannas are usually located between desert b. Orchards. An area of orchards or planta- and forest regions. tions usually consists of rows of evenly spaced c. Prairie. The prairie type of grass occurs trees, showing evidence of planned planting most frequently in areas where the soil remains that can be distinguished on an aerial photo- moist for a depth of 75 centimeters (30 inches) graph. Usually such an area is free from or more. The prairies are covered with tall, underbrush and vines. luxuriant, and relatively deep-rooted grasses c. Rice Fields. Rice fields usually are flooded that grow to heights of from 30 to 90 centi- areas surrounded by dikes or walls approxi- meters (1 to 3 feet). Over most prairie regions, mately 1/2 or 1 meter (1Y2 to 3Y2 feet) in rainfall varies between 50 to 100 centimeters height and Y2 to 11/2 meters (11/2 to 41/2 feet) (20 and 40 inches) annually. Usually there is wide. When flooded for planting, the depth to a large variety of flowering plants in spring the bottom mud ranges from 15 to 90 centi- and summer. The principal prairie regions in- meters (6 inches to 3 feet). clude parts of central United States and the prairie provinces of Canada; the Argentine 90. Military Aspects Pampa, Uruguay, and southeastern Brazil; the plains of the Danube in Hungary and Rumania; a. Key Terrain. Woods provide concealment and parts of Manchuria and southern Russia. and cover for assembly areas and during the approach march. Forests and heavy vegetation, d. Steppe. A steppe is an area of short, however, increase the difficulty of maneuver in shallow-rooted grasses typical of semiarid re- advancing to attack and in launching the as- gions where the depth of moist soil is less than sault. The attacker may have little or no 60 centimeters (2 feet). In common usage, the information about the roads, trails, and topog- word steppe is used to describe all the drier, raphy in the area not under his control, due short-grass grasslands, both in tropical and to the difficulty of securing detailed terrain middle latitudes. Some of the steppe grasses intelligence without actual reconnaissance. lie in a soft, fine mat on the ground, while Wooded and heavily vegetated areas provide others stand as hard, wiry tufts. Thorny shrubs cover and concealment for organized positions, and low, coarse bushes may dominate the steppe shelter for reserve formations, and an obstacle in some sections. Cacti and other succulent to the attacking forces. Usually the defender

89 is able to make a detailed reconnaissance of influence of forests and heavy vegeta- the area, so that he is familiar with the roads, tion upon nuclear weapons effects trails, and other features of the terrain. In- varies with the amount of overhead fantry weapons form the basis of the defense, cover, density of growth, kind of due to the difficulty of securing observed ar- trees, nature of the tree crowns, un- tillery fire in heavily wooded areas. dergrowth, and the litter on the forest b. Observation and Fields of Fire. floor. Trees in leaf offer a high degree of protection from thermal radiation (1) Observation. The height and density if the cover is sufficiently continuous, of the trees and other vegetation but protection from initial nuclear largely determine the amount of radiation is insignificant. ground observation that can be obtained. To secure an adequate field of c. Cover and Concealment. Thick forests of view from an observation post, it may deciduous trees in leaf give excellent conceal- be necessary to clear away vegetation ment from air observation when troops observe at the risk of losing concealment. The proper precautions in camouflage and move- effects of cultivated crops upon ob- ment. Evergreen forests will provide conceal- servation vary with seasonal condi- ment throughout the year, changing color very tions. In two or three weeks a corn- slightly from season to season. Deciduous trees field may be covered with high stalks lose their leaves, reducing concealment, and that limit observation. Later in the change color, which increase the difficulty of season, this corn may be harvested in natural camouflage. Usually undergrowth and a day, allowing observation again. small trees growing closely together give better (2) Fields of fire. Lanes may be cut concealment from ground observation than a through vegetation to provide fields stand of larger trees. Unless the undergrowth of fire, but it is seldom practical to is high, however, it will provide little conceal- cut lanes that extend far enough to ment from aerial observation. The amount of provide long-range observed fires. Ex- concealment and cover provided by cultivated tensive clearing indicates the location crops depends largely upon seasonal conditions. of weapon positions to the enemy. The Disruption of the agricultural pattern is readily extent of clearing that is practicable apparent to aerial observers and in aerial will depend upon the amount of vege- photographs. tation, its density, and the length of d. Obstacles. Fire lanes and certain types of time that the positions will be occu- vegetation often canalize movement through pied. Indirect fire is less affected by forest areas. This is true, for example when vegetation than direct fire. Mortars lines of trees border streams. Normally, no require little more than overhead serious obstacle to movement is offered by clearance. Artillery weapons require shrubs and grasses, but visibility can be re- more clearance than mortars, but duced in high grasses, with the added danger high angle fire may be employed to of reptiles to foot soldiers. Small grain crops avoid extensive cutting and clearing. hold soil nearly as well as grasses, so that Air defense artillery can be employed movement is better in such areas than in those effectively in forests and areas of planted with row crops. Some parts of vine- heavy vegetation when clearance re- yards present a tangled maze of poles and wires quirements are met. Forests and heavy that constitute a definite obstacle to vehicles vegetation may be set on fire as a and dismounted troops. The terraces and re- tactical weapon, particularly during taining walls on hillsides are also obstacles. dry season. Wooded areas and those Wheeled vehicles and some tracked vehicles are covered with heavy vegetation tend unable to cross flooded paddy fields, although to increase the persistence of gas and they can negotiate them when the fields have smoke, particularly during wet sea- been drained and the soil is thoroughly dry. sons or periods of high humidity. The In some cases even dried paddy fields remain 90 a serious obstacle to movement because some Deeper taproots are developed where the vehicles are unable to negotiate the dikes sur- permafrost is far below the surface. rounding the fields. 91. Information Requirements-Vegetation e. Avenues of Approach. In most wooded areas, individual trees large enough to stop a As far as practicable, information about the tank are seldom so close together that they vegetation in an area is presented in the form cannot be bypassed. Closely-spaced trees usu- of a map overlay that clearly indicates and ally are of relatively small diameters and can identifies the major vegetation types by the be pushed over by a tank. The smaller trees use of color and symbols. The accompanying and undergrowth, however, may be so dense text briefly summarizes the additional infor- that when they are pushed over the resulting mation of military significance that cannot be mass of pileup vegetation will stop the tank. shown adequately on the map. Pertinent infor- In most cases, wooded areas slow down the mation may include the following: movement of tanks, and a guide may be re- a. Forests. quired to lead each vehicle. Cutover portions of wooded areas usually contain stumps hidden (1) Name or other identification. in tall grass or weeds that are serious obstacles (2) Plant associations. to armor. Trees that can stop a wheeled ve- (3) Principal species (names, proportion hicle usually are too closely spaced to be by- in percent, density or average spac- passed. The pileup effect from pushing over ing, height range). vegetation is greater for wheeled vehicles than for tanks. Trailed loads are difficult to tow (4) Undergrowth species. through wooded areas. Woods slow down the (5) Canopy: structure (continuous, open, movement of dismounted troops. Some types of broken) and seasonality (color, de- vegetation, such as mangroves or dense jungle, foliation). are frequently impenetrable until routes are (6) Duff (partly decayed vegetable mat- cleared. ter on the forest floor): abundance f. Construction.The usefulness of trees for and nature of fallen trees, logs, and timber is determined by their height and so on. diameter, and by the nature of the wood as hard, soft, or fibrous. Deciduous trees generally (7) Exploitation practices (normal cut- are hardwoods. Needleleaf trees are softwoods ting, overcutting, undercutting). that usually are easily worked, although some (8) Operational aspects (suitability for species are fibrous and difficult to saw. When a cover, concealment, blowdown sus- forest area must be cleared of trees prior to a ceptibility, camouflage, and fuel). construction project, a study of the ground will indicate the density and depth of the root (9) Principal tree species. systems. Where a forest is closely underlain by (a) Name (English and botanical). hardpan or rock, tree roots branch and remain (b) Height (average). near the surface, making them easy to uproot. (c) Growth form (triangular, linear, In soil that is firm, with deep underlying rock, and ovate). trees tend to form large taproots extending to a considerable depth, making them diffi- (d) Diameter (average). cult to remove. Trees in inundated, marshy, (e) Leaves (broadleaf or needleleaf). and muskeg areas have thick widespreading (f) Period of defoliation. and shallow root systems near the surface of (g) Roots (structure, size, toughness). the ground. In northern regions where permafrost occurs, its effect on the root systems of (h) Suitability for construction. trees is similar to that of hardpan or rock. (i) Special features (toxicity, thorni- Where the permafrost is near the surface, the ness, edibility). roots branch and lie close to the surface. (j) Indicator significance relation to 91 regional and local climates, kind (e) Suitability as forage. and state of ground, and ground (f) Special factors (toxicity, irri- water, salinity, permafrost, depth tancy). and duration of snow cover, human (g) Indicator significance. activity). d. Cultivated Crops (general). b. Shrubs. (1) Location and areal extent. Location and areal extent. (1) (2) Name or other identification. (2) Name or other identification. (3) Principal crops (names, proportion (3) Principal species (names, proportion in percent, density or spacing height in percent, density or average spac- range; if applicable, months planted, ing, height range). cultivated, and harvested; crop rota- (4) Foliage-density and seasonality tion practices). (color, defoliation). (4) Canopy, foliage, or stand (as applica- (5) Operational aspects (susceptibility to ble: structure, color, defoliation, den- mass conflagration). sity, rates of growth). (6) Principal shrub species (for each). (5) Types of farming (irrigated, dry, and (Same information as for tree so on). species.) (6) Special factors associated with crops c. Grasses. (irrigation ditches, flooding, terraces, (1) Location and area extent. hedgerows, dikes, and stone or other types of fences). (2) Identification. (7) Operational aspects (susceptibility to (3) Principal species (names, proportion mass conflagration). in percent, density, height range). (4) Seasonality (dates of growth, color). (8) Principal crops. (5) Operational aspects (susceptibility to (a) Tree and shrub crops (same infor- mass conflagration). mation as for tree species; in addition, months that the crops are (6) Principal species (for each). harvested). (a) Name (English and botanical). (b) Grass and grain crops (same infor- (b) Date of maturity, height. mation as for tree species; in addi- (c) Life span. tion, months of planting and har- (d)Growth habit (sod or bunch). vesting).

92 CHAPTER 6 MANMADE TERRAIN FEATURES

Section I. SIGNIFICANCE

92. Definition 93. Military Aspects Manmade features include all the changes In preparing terrain studies, manmade fea- in the natural environment made by man in tures must be evaluated to determine their the course of living on the earth and using its effect upon the military aspects of proposed resources. Major manmade features are cities, operations. Recommendations may be made to defensive works, transportation and communi- destroy certain features or to retain them for cation facilities, and similar features that have significant effects upon the military opera- future use after the operation has been com- tions. Others are such features as cemeteries, pleted. Usually each major manmade feature hedgerows, and buildings, which affect only is the subject of a detailed study by military local operations. intelligence personnel.

Section II. LINES OF COMMUNICATION 94. Importance 95. Roads and Routes The lines of communication of an area con- a. Description. The term roads includes all sist of all the roads, railways, and waterways types of roads and tracks, but pack trails and over which troops or supplies can be moved. foot paths are not included. Bridges, ferries, The importance of particular features will de- snowsheds, and similar structures and facil- pend upon the unit and the type of operations. ities that provide continuity of movement and The ability of an army to carry out its mission protection for the way are also considered as depends greatly upon its lines of communica- integral parts of the road system. An adequate tion. One of the primary considerations in road system is a fundamental requirement in planning large-scale operations is the extent the conduct of any major military operation. and general nature of the transportation net- Terrain studies must provide information work. Planners must consider the advantages about the roads which exist in the area under and disadvantages of the entire pattern of consideration and should indicate any major transportation facilities. An area with a dense repair or rehabilitation required on existing transportation network, for example, is favor- roads, or where now roads will be needed to able for major offensives. One that is criss- support a proposed operation. Roads in the crossed with canals and railroads, but pos- combat zone usually need meet only minimum sesses few roads, will limit the use of wheeled standards, but those in rear areas, especially vehicles and the maneuver of armor and in the vicinity of water terminals, airfields, motorized infantry. Railroads extending along supply installations, and those used as MSR's the axis of advance will assume greater impor- must be well-surfaced and capable of carrying tance than those perpendicular to the axis, and heavy vehicle traffic without excessive main- the direction of major highways and water- tenance. Operations on a wide front and the ways assumes equal significance. employment of nuclear weapons will require 93 a large number of secondary roads in both able in adverse weather and cannot forward and rear areas. The information pre- be kept open by maintenance short sented in a terrain study should indicate the of major construction. This type of minimum maintenance and construction re- route is so seriously affected by quirements that may be anticipated during a weather that traffic may be brought planned operation. Continual maintenance of to a halt for long periods. In this route road net is essential. In addition to the severe class are roads of natural or stabil- punishment given to roads by large volumes of ized soil, sand-clay, shell, cinders, heavy traffic, important bridges, intersections, laterite, and other lightly metalled or and narrow defiles are primary targets for light aggregate surfaces. enemy bombardment. The maintenance of un- c. Location necessary roads must be avoided, and the con- and Use. Military routes are classified also as follows: struction of new roads held to a minimum. (1) Axial route. Axial route is part of b. Route Types. Routes usually are classified military road net work, and it leads as follows: toward the front and is generally (1) All-weather route (Type X). Any perpendicular thereto. When desig- route which with reasonable main- nated as the principal traffic artery tenance is passable throughout the of a division or higher unit, such a year to a volume of traffic never ap- route is termed a main supply route preciably less than its maximum ca- (MSR). When designated the prin- pacity. The roads which make up this cipal traffic artery of a brigade or type of route have a waterproof sur- battalion, such a road is termed a face, adequate drainage, and are only supply route (SR). slightly affected by precipitation or (2) Lateral route. A route which gener- temperature fluctuations. At no time ally parallels the front and leads into is it closed to traffic by weather ef- and across axial routes. fects other than snow blockage. In this route class are roads paved with (3) Reserved route. A controlled route concrete, bituminous surfacing, brick, allocated exclusively to a command or or paving stone. unit, or intended to meet a particular requirement. (2) All-weather route (Type Y) (Limited traffic due to weather). Any route (4) Supervised route. A route over which which with reasonable maintenance control is exercised by means of traf- can be kept open in all weather, but fic control posts, traffic patrols, or sometimes only to traffic considerably both. less than maximum capacity. The (5) Dispatch route. A route over which roads which form this type of route full control, both priority and regula- do not usually have waterproof sur- tion of traffic, is exercised. faces and are considerably affected d. Adverse Terrain. Swamps, bogs, and low- by precipitation or temperature fluc- lands such as delta areas may create special tuations. Traffic may be halted com- problems of drainage and ditching, necessitate pletely for short periods. Heavy use added support to the roadbed and require the during adverse weather conditions construction of many bridges. Rugged topog- may cause complete collapse of the raphy may result in steep grades and sharp surface. Crushed rock or waterbound curves, tunneling, bridging, cuts, and sidehill macadam, gravel, stabilized soil, or locations in laying out new roads. Sidefiill lo- sand-clay, are typical roads in this cations, in turn, may require retaining walls, route class. cribbing, and snowsheds to give protection (3) Fair-weather route (Type Z). A against earth, rock, or snow slides. In the des- route which quickly becomes impass- ert, sand fences and special crews and equip- 94 ment to keep the roads clear of drifting sands map overlays that show the alinement of the may be required. Arctic terrain requires spe- significant roads, with the location of associ- cial techniques to build and maintain roads on ated bridges, tunnels, ferries, fords, and criti- permafrost and periodically frozen ground. cal points such as rockslide areas. Ordinarily numbers is used, but e. Weather and Climate. Sustained periods the local system of route for of freezing, heavy snowfalls, and similar ex- if no system exists that is satisfactory arbitrary treme weather conditions may seriously affect terrain intelligence purposes, an system is used to identify the main and sec- the use, maintenance, and construction of roads. Protection must be provided against ondary roads. snow drifts, and provisions made to remove b. Information about individual roads usu- the snow and to repair damage due to frost ally includes the following: heave and frost boils. Excessive rainfall may (1) Name and route number. result in washouts and flooding in low areas and cause earth and rock slides in rugged ter- (2) Terminal points; intermediate local- rain. Continuous wet weather may make un- ities on the road; distances between surfaced roads impassable. In dry periods, dust major points. control becomes an important factor on un- (3) Terrain (elevations, irregularities, surfaced roads. slopes, drainage, soils). f. Design and Construction. Terrain studies (4) Length and width. should include an engineering evaluation of the (5) General condition (necessary repairs structural soundness of all roads in an area and improvements, with nature and under consideration. If the initial design did location). not provide for the increased loads and speeds that would accompany military use or if the (6) Surface material (by sections, if road was improperly constructed originally, it there are changes in type of surface may prove a serious obstacle to movement. Re- along the route). pairs and excessive maintenance may be re- (7) Ratings of alinement, drainage, foun- quired because of an unstable subgrade; inade- dation, and surface. quate drainage of the subgrade, surface, or (8) Roadbed (width of traveled way; type slopes; sharp curves, and loose or unsealed and width of shoulders). wearing surfaces that result in saturated road- beds. (9) Maximum grade. g. Poor Maintenance. Poor maintenance of a (10) Sharpest curvature. road is shown by clogged culverts and ditches, (11) Significant cuts and fills. potholed, bumpy, and rutted surfaces, soft and (12) Clearance (minimum vertical and uneven shoulders, and badly worn and cracked horizontal clearances, with nature of pavements. Studies should indicate where restrictions). these conditions exist and the maintenance that would be required to bring the roads up (13) Bridges (load capacity, general con- to minimum military standards. dition). h. Trafficability. The various types of soils (14) Tunnels (length, widths, clearances, affect trafficability differently. For example condition). sandstone affords excellent trafficability when (15) Fords and ferries (type, general it is dry but is reduced to good trafficability characteristics, condition). when,wet; trafficability on a clay surface is (16) Critical points; location and charac- rated as fair when dry and impassable when teristics of possible bypass routes or wet. " detours around bottlenecks. (17) Location and characteristics of routes 96. Information Requirements - Roads that provide maximum protection a. Information about roads is recorded on from ground or air attacks. 95 (18) Snow (critical areas, snow fencing, cover while awaiting their turn to snow removal equipment). cross.

97. Bridges 98. Information Requirements - Bridges a. Importance. Road and railway bridges are a. Detailed information about bridges can- vulnerable points on a line of communication. not be obtained from topographic maps, but Timely preservation, destruction, or repair of indications on air photographs usually will a bridge may be the key to an effective de- permit an approximate determination of the fense or to successful penetration of an enemy width, clearance, and height above water of a area. A bridge seized intact has great value in bridge. Details such as the condition, capacity, offensive operations, since even a small bridge and structure of a bridge should be obtained facilitates the movement of combat troops by engineer reconnaissance. Reconnaissance across a river or stream. Information about procedures are described in TM 5-312 and FM bridge types and their classification is con- 5-36. Basic information requirements for a tained in TM 5-312 and FM 5-36. bridge should include a summary of its structural characteristics, its critical dimensions b. Sites. Because of the time and labor in- (length, usable width, overhead clearance), an volved, new bridges are erected only when an estimate of capacity, and general condition. existing bridge, ford, or detour cannot be used. Terrain suitable for a bridge site should meet b. Detailed information includes the follow- the following requirements: ing: (1) Type, number of lanes and width of (1) Satisfactory river conditions, with no each, number of spans and length of fast currents or great depths. each length of panels, arrangement (2) Site readily accessible from the road of spans. it serves. (2) Height above riverbed, overhead (3) Firm, well-drained approaches, pref- clearance for vehicles, class. erably above flood level. (3) Stream data: width, depth, velocity (4) For floating bridges, a riverbed free of current, direction of flow, type of from snags, rocks, and shoals to a bottom, estimated bearing capacity of minimum depth of three feet and bottom, height, slope, and nature of firm enough to hold anchors and to banks. support trestles. Banks should be (4) Description, dimensions, and condi- from two to six feet above water level tion of access roads and approaches. to minimize excessive abutment prep- (5) Type, dimension, and condition of aration. abutments, stringers, flooring, gird- (5) Firm, stable banks of suitable height. ers, and other structural elements. Large differences in bank height re- (6) If damaged or wrecked- quire excessive grading. Low banks (a) Structural details of bridge in its may be subject to a rising river level original form. that will flood the bridge site. (b) Nature and extent of damage; po- (6) Adequate, well-drained working sition of debris; details regarding areas close to the site including a any salvageable materials. bivouac for the working party, space (c) What loads, if any, can still cross for construction materials, and turn- the bridge. arounds and parking places for ve- (d) If not suitable for use, information hicles and heavy mobile equipment. about alternate sites. (7) Areas close to the site, near or alongside the approach roads, where ve- 99. Railways hicles can park off the road and under a. Property. The term railway includes all 96 fixed property belonging to a line, such as f. Military Use. Railways are desirable for land, permanent way, bridges, tunnels, and extended military operations. Their capabili- other structures. Railways assume increased ties are of primary concern and are the sub- military importance in areas where the soils ject of continuing studies by personnel at the are generally untrafficable, roads are poor, and highest levels. Detailed intelligence about the rail transportation facilities are extensive. railways in an area of operations is produced Frequently, railways can be used as substitute by specialists of transportation and engineer roads fo) vehicles. Most railway bridges will units. Railways are highly vulnerable to enemy carry"ta4hks without reinforcement. The basic attack, particularly to sabotage and guerrilla elements of a railroad include motive power, operations. Keeping a railroad line in operation rolling stock; trackage; yards, terminals, regu- requires trained security forces and extensive lating stations, and railheads; transshipment protective measures. points; water and fuel stations; maintenance and repair facilities; and signal communica- 100. Evaluation of Railways tion facilities. In evaluating a railway for terrain intelli- b. Yard. A yard is an area containing a sys- gence purposes, consideration should be given tem of interconnected tracks and is used for to the effects of adverse terrain, weather and making up trains, storing cars, and general climate, and the overall design and construc- maintenance activities. tion of the system. The following factors should be considered: c. Railhead. A railhead is the point at which supplies destined for a particular unit, instal- a. Adverse Terrain. Railways passing over lation, or area are transferred from rail to an- swamps, bogs, and delta terrain may encounter other type of transportation, usually trucks. special problems of drainage, ditching, and roadbed maintenance. In mountainous areas, d. Regulation. A regulating station is an steep grades, sharp curves, and tunnels are installation on a military railway line at which common. Because of sidehill locations and deep the movement of supplies and personnel is cuts, there should be protection against earth, controlled. Its facilities include a yard, open and rock, and snow slides. In desert, drifting sand covered storage, and usually, temporary hous- is a problem and provisions should be made to ing and messing facilities for transient per- remove it. sonnel. b. Adverse Weather and Climate. Severe e. Construction. The development and extent winter conditions seriously retard operation of a railway system largely reflect the topog- and maintenance of railways, requiring pro- raphy of the region that it traverses. In desert tection against drifting snow, provisions for regions, for example, a single railroad may ex- snow removal, and repairs because of damage tend in a straight line across vast barren caused by frost heave. Excessive rainfall may wastes. In hill regions and mountain areas, the result in washouts and flooding in low areas railways run through valleys, with short lines and cause earth and rock slides in rugged ter- leading off into other terrain. On plains, rail- rain. ways will have few curves but may be subject to the effects of poor drainage conditions. Gen- c. Design. A railway may prove inadequate erally, railways tend to follow rivers because because the initial design did not provide for of the more uniform grades, the availability of the increased loads and speeds or heavier straight routes, and the concentration of re- volume of traffic needed. As a result, a railway sources, industries, and population centers might require either considerable reconstruc- along the waterway. The terrain characteris- tion and repair or extensive maintenance. tics of an area can be determined to a consid- Among the more common defects are an un- erable degree by a study of the railway routes, stable subgrade, lack of adequate drainage, since the rail lines almost invariably follow light rail, poor ballast, and untreated ties. Im- the topography that offers the fewest obstacles. proper maintenance is evidenced by such con- 97 ditions as an uneven roadbed, improperly (4) Gage. tamped ties, loose fastenings, badly worn rail, (5) Number of tracks. or uncleared drains. (6) Weight of rails. 101. Information Requirements - Railways (7) Maximum grade and minimum radius of curvature with location of Railway information should be recorded on each. a map or overlay that shows the true alinement of all rail lines; their trackage, gage, and (8) Ties, ballast. status; and the location of selected bridges, (9) Sidings and passing tracks (location, tunnels, and ferries. A convenient system of lengths, switches). line numbers is used based on a standard ref- (10) Tunnels (locations, clearances). erence or arbitrarily selected. Fundamental information about railways should include the (11) Overhead structures and vertical following: clearances. (12) Drainage facilities, including cul- a. Total mileage. verts. b. Terminals and details of main lines. (13) Bridge data. c. Mileage by gage and locations of changes. (14) Operating and servicing facilities (location, availability of fuel and water d. Number of tracks. and ice; signal, traffic control, and e. Maximum grade and minimum radius of dispatching facilities). curvature. (15) Availability of trained and depend- f. Location and length of passing tracks. able personnel. g. Type and weight of rail. (16) Transshipment points. h. Permissible loads; capacity of bridges. q. Equipment. i. Yards and terminals (location, type, ca- (1) Present condition, and interchange- pacity). ability with equipment of other countries. j. Details of servicing facilities and other (2) Motive power (type, size, weight, installations. tractive effort, wheel arrangement, k. Operating factors (cars per train; speed; type and height of couplings). number of daily trains each way). (3) Rolling stock (type, number, car di- 1. Bridges and tunnels (bridge data to in- mensions, capacity, weight). clude length, number of tracks, spans by type (4) Rail cars self-propelled and trailer- and length, height of structure; tunnel data to type, total by type, size, capacity. include length, number of tracks, and lining). (5) Work cranes (total by type, size, m. Rail ferries (location, type, capacity). capacity). n. Electrification (location, type). (6) Snow plows (total by type, size). o. Transshipment points. (7) Armored equipment (total by type, size). p. Individual rail line details- (8) Repair shops (location, types of (1) Name. equipment repaired, capacity by type, (2) Terminals, intermediate stations, number of personnel employed). length of each stretch. (3) Obstructions (demolitions, washouts, 102. Inland Waterways blocked tunnels). a. Definition. The term inland waterway is 98 applied to those rivers, canals, lakes, and in- Streams of low and uniform gradients usually land seas of a country which are used as ave- meander. Their channels shift constantly, de- nues of transport. It includes all the fixed positing sandbars, which are a menace to structures which affect the movement of ves- navigation. sels carrying passengers or freight. Types of inland waterways include inland lakes and 103. Information Requirements - land-locked seas, rivers, and ship and barge Waterways canals, and the intracoastal waterways, usu- Inland waterway information should be really running parallel to the coastline of a land corded on a map or overlay that shows the true mass and sheltered enough to permit the navi- alinement of the navigable waterways, the lo- gation of small vessels. cation of all locks, dams, aqueduct bridges, tun- b. Classification. Inland waterways can be nels, and major landing facilities, and the which limit the classified according to their depths as follows: location of specific structures vertical and horizontal clearances on each (1) Very shallow. Depths less than 1.4 navigable reach. The local names are used to meters (41/2 feet). identify waterways and structures whenever (2) Medium. Depths between 1.4 and 2 feasible. Detailed information requirements meters (41/2 and 6V2 feet). should include the following: (3) Deep. Depths greater than 2 meters a. Developed Waterways. (6V2 feet). (1) Geographical location (name, origin, c. Advantages. Inland waterways provide an terminus, length). economical form of transportation for bulk (2) Restricting widths and depths of supplies, freeing faster modes for shipments channel. of a higher priority. Frequently, large or very heavy items that cannot be handled by truck (3) Frequency, duration, and effects of and rail can be shipped by waterway. One of seasonal changes (floods, low water, the major uses of waterways in an active droughts, excessive currents, normal theater is the transportation of supplies for freezeup and opening dates). the rehabilitation of the economy in liberated (4) Location, description, and restrictive areas, thus reducing the demands upon mili- effects of structures (locks, safety tary transportation facilities. gates, dams, bridges, ferry crossings, d. Limitations. Unless icebreaking operations aqueducts, tunnels, cable crossings). can be conducted, traffic is halted completely (5) Speed and fluctuation of current. during a freezing period. The thaw following (6) Name and location of waterway a freezeup may cause floods, and periods of ports, including length of alongside drought may result in insufficient water for wharfage and depths, and data on the movement of vessels. The locks, bridges, mechanical handling, storage, clear- cuts, dams, and other facilities are vulnerable ance and ship repair facilities. to enemy action. Retreating enemy troops usually drop rail or road bridges into the water- (7) Maintenance requirements. way; damage locks and levees; obstruct chan- (8) Craft (number, type, cargo capaci- nels with ships and barges; drain canals; and ties). destroy, dismantle, or move essential equip- (9) Communication facilities. ment. Waterway transport is slow. It is also inflexible, since new waterways cannot be (10) Availability of labor force. constructed during military operations. The b. Navigable Rivers. In addition to the depths of rivers and streams used as water- items listed in a above, the following addi- ways fluctuate with maximum and minimum tional information may be required: rainfall. Streams with fairly direct courses commonly are interrupted by falls and rapids. (1) Physical characteristics of the river 99 (bottom, banks, feedwater streams, (buoys, lights, range markers, radar, and important tributaries). foghorns). (2) Navigational hazards, such as falls, rapids, and sandbars. (4) Changes in channel. (3) Navigational aids, location, and type (5) Dredging requirements.

Section III. PETROLEUM AND NATURAL GAS

104. Location b. Refineries are located near either producing a. Source. Oil is found only in the stratified oil fields or distribution centers in major consuming areas. Adequate sedimentary rocks and all-weather trans- sands of ancient sedi- portation and an abundance of cooling water mentary basin areas. Because of geologic up- are essential. Tall, cylindrical distillation or heavals in past ages, today's oilfields may be "cracking" towers are the most prominent found along the foot of mountain chains or in features at refineries. Other equipment includes lowland or offshore areas. Petroleum, gas, and large furnaces, cooling towers, electric power water are commonly found together. plants or substations, and intricate piping b. Gas. Natural gas is found alone, as well systems. Tankage for storing crude oil charge as with petroleum. Gas from oil wells is com- stocks and semirefined and refined products is monly entrained with natural gasoline and is also required. Refinery capacities are usually known as wet gas. When economically feasible, rated in barrels per day (42 U.S. gallons per wet gas is piped to an absorption plant, where barrel) or metric tons per year of crude oil the gasoline is extracted. Gas from gas wells run to stills (crude oil started through the ordinarily is relatively free of natural gasoline refining processes). A reliable rule of thumb and is known as dry gas. If sufficiently free of for converting barrels per day to metric tons other unwanted gases and impurities, dry gas per year is to multiply the number of bar- may be fed directly into pipelines for distri- rels per day by 50. Metric tons per year are bution. divided by 50 to yield barrel-per-day figures. Crude oil for refinery fuel or lost otherwise amounts to about 7 to 10 percent of refinery 105. Installations capacity. a. Derricks are commonly the most distin- guishing features of an oil or gas field. A der- 106. Distribution rick is required to position and handle the long sections of drill pipe and other equipment a. Systems. A bulk distribution system for used in the well when drilling for oil. Depend- petroleum products may include ship-to-shore ing on the type, the cost of moving or future and dockside loading and unloading facilities, needs, a derrick may or may not be left in bulk storage tank farms, pipelines, pumping place indefinitely following the completion of stations; bulk delivery points or pipeheads, the well. Where warehouses, open storage areas, canning and a continuing need exists, the drumming drilling derricks may be replaced with smaller facilities and testing laboratories. Ocean-going tankers, derricks or gin poles. A producing oil well is tank barges, railroad characterized by a pump or by a tank cars, and tank trucks are also included "Christmas in integrated distribution tree," so called because systems. For terrain of its tree-like appear- intelligence purposes, pipelines ance. A pump is used where the subterranean and storage facilities are the most significant features of gas pressure is too low to force oil to the sur- a distribution system. face. A Christmas tree is used where the underground gas pressure is sufficient to force oil to b. Pipelines. Pipelines commonly consist of the surface. It consists of a system of pipes, piping, pumping equipment, and regulating valves, and gages capping a well for controlling tankage. Other supporting equipment may in- the flow of crude oil and gas. clude tele-communications facilities, cleaning 100 devices and trays for removal of unwanted the product stored. The tanks may be corn- condensates or contaminants, control and heat- pletely above ground, partly or entirely buried. ing devices. The capacity of a pipeline is ex- Tanks above ground are surrounded by dikes pressed as a quantity of liquid capable of being or low walls to form catch basins and to pre- transported per unit of time, ordinarily in the vent the occurrence or spread of fires if the number of barrels, metric tons, or cubic meters tanks are ruptured or overflow. Tanks are per day. The quantity of fuel actually trans- buried or partly buried for reason of safety, to ported, usually will not exceed about 85 percent reduce evaporation losses, for concealment, or of the pipeline capacity. to reduce their vulnerability to military attack. c. Military Pipelines. Military pipelines are A group of storage tanks is called a tank farm. Tank farms vary greatly used chiefly to transport jet fuel and gasoline. in size; some comprise Occasionally they are used also to transport major storage complexes, with storage capaci- diesel fuel and kerosene. Commonly, 15-cm ties of millions of barrels. Ordinarily, the tanks (6-inch) pipe is used; 20-cm (8-inch) pipe is are interconnected by an assembly of pipes and employed for ship unloading or trunk lines. valves called a manifold, which permits the The pipeline follows the most direct level route, movement of products. Because of their vulner- within six to nine meters (20-30 feet) of all- ability to air attack, and to nuclear attack, weather roads, so as to facilitate construction, military tanks farms are limited to a total partrol, repair, and security of the line. Cross- capacity of no more than 250,000 barrels. country cutoffs are used where roads wind Military storage tanks are made of steel or excessively. A military pipeline is diverted aluminum and have capacities up to 10,000 around difficult terrain, such as marshes, barrels. Portable fabric tanks also are used swamps, or land that is subject to periodic in military operations at forward supply points flooding. It also avoids populated areas and and at beachheads. military installations that have a high element of hazard, such as ammunition dumps. Base 107. Military Importance terminals are located in rear areas, at or near a. Targets. The petroleum and natural gas theater ports of embarkation or other tanker resources of a country or region are valuable unloading points, but pipehead terminals are assets to its economy, and the degree of self- located at the forward end of a military pipe- sufficiency in military fuels is fundamental to line, moving forward with the army supply its conventional military capabilities. Accord- point to support the advancing forces. ingly, refineries, terminal facilities, distribu- d. Civilian Pipelines. Civilian pipelines are tion systems, and storage installations are important for potential military support. They primary targets for air attack and are major are generally permanently installed cross-coun- objectives. Major oil producing areas and re- try along the most economical route. These pipe- fineries, key pipelines, storage facilities, and lines may range from about 10 cm (4 inches) marine terminals may be the principal ob- to more than 100 cm (40 inches) in diameter. jectives of a campaign to seize them for our use Pipe of extremely large diameter is ordinarily or deny them to the enemy. The most militarily used only for natural gas or crude oil. Pipe- significant natural gas facilities are pipelines, lines for crude oil are much more common which could be readily converted for handling than those for refined products, although use petroleum products for military support. of the latter is rapidly growing. Crude oil pipelines can be converted for handling refined b. Planning. Because military planners are products. This is a costly and time-consuming interested in the availability of fuel for mili- undertaking, particularly if aviation-grade tary use, avoiding possible disturbance to fuels are to be transported. local economics, the typical normal operating conditions with respect to petroleum facilities e. Tanks. Bulk petroleum and refined pro- are important. Included are seasonal variations ducts are stored in tanks which differ greatly in the supply and demand for petroleum pro- in size, shape, and construction, according to ducts, and the principal consumers and their the function of the tanks and the nature of needs. Manufacturing and civil transport

101 fuel requirements, as well as agricultural con- (1) Location and owner/operator. sumption by tractors and irrigating systems (2) Capacity. are militarily significant in modern planning. (3) Details of construction; type of equip- 108. Information Requirements - Petroleum ment. and Natural Gas (4) Nature and quality of products produced. The location and extent of petroleum and gas facilities should be recorded on a topo- c. Pipelines. graphic map of suitable scale. A numbering system is established to identify the petroleum (1) Name, if any; location of lines; material transported. and the gas pipelines, producing fields, plants, and storage facilities. A separate series of (2) Terminals. numbers is used for each pipeline. Such pipe- (3) Number and diameter of pipes; line facilities as pumping stations and tank delivery capacity of system at present farms are numbered serially, beginning from and under normal conditions; content a designated initial point on the line. Local of pipeline when full. names may be used for individual installations. Basic information should include the following: (4) Facilities at base terminal (if a water terminal, method of loading from a. General. tankers). (1) Location and type of raw material (5) Storage facilities at terminals and (oil, oil shale, natural gas) ; character along pipelines; capacity of each in- of crude oil; well logs; and a geologic stallation. column which designates the produc- (6) Pumping stations (location, capacity, ing formations and the depth to pro- equipment). ducing horizons. (2) Reserves of raw material in million d. Storage. barrels, metric tons, or million cubic (1) Location: geographic coordinates; to- feet (cubic meters). pography; adjacent landmarks. (3) Administrative, maintenance, and re- (2) Surface tanks: types and number; pair facilities. dimensions; protection (revetments, (4) Security and safety provisions. blast walls). (5) Physical condition of installations number; dimensions. and equipment; required major re- (3) Buried tanks; pairs or improvements. (4) Pump houses: location; number; (6) Availability of trained and reliable dimensions; capacity. personnel. (5) Connecting pipelines and distributing (7) Principal consumers. systems. b. Refineries. (6) Stocks (location and type).

Section IV. MINES, QUARRIES, AND PITS 109. Mines coal, lignite, and peat. Terrain studies list each significant mineral, covering in detail the a. Mineral Resources. The important mineral estimated quantities available and the methods resources of a country include metallic ores and facilities employed to mine, process, and such as iron, copper, zinc, lead, tin, silver, gold, distribute each type of mineral. Mineral de- and uranium; mineral deposits, principally posits are exploited either from the surface of sulfur, phosphate rock, gypsum, graphite, as- the ground or from underground shafts and bestos, and bauxite; and solid fuels, chiefly tunnels, the method depending upon the depth 102 of the deposit below the surface. A typical mineral being removed by power shovels. underground mine consists of a vertical shaft, b. Placer.Placer mining involves the removal horizontal passages opening out of the shaft, of the unconsolidated rock material that lies and passages driven from above (winzes) con- above bedrock by hand, hydraulic nozzles or necting the levels. Openings branching off from dredges, and subsequent separation of the the levels, where the ore is actually extracted, ore from waste by panning and sluicing. It is are called stopes. Supports in mine working widely employed to mine gold. usually are made of timber treated with pre- c. Open-pit. In open-pit mining, an excava- servatives or of reinforced concrete, steel, brick, tion is made. In the case of deep pits, the sides or stone. Pillars of ore may be left as supports, usually are cut into steps or benches. Access finally being mined when the workings are to the below-ground-level site may be obtained vacated. Where ore beds lie close to the surface, by arranging these benches in spiral form, by the mineral may be removed from open pits cutting inclined approaches, or by sinking a after stripping off the overlying earth and shaft connected to the mine by an adit or tun- rock. This is strip mining, the coal or other nel (fig. 48).

~~~~~- - -"----

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II-;1~ Ili -'l ';- - ~ - I

_ _ "Y-~~~~P~~~r~~-- . . Figure 48. Open-pit copper mine. d. Glory-Hole. In glory-hole mining, the ex- a major objective for air attack. The seizure or cavation is funnel-shaped, and a vertical pas- defense of important mines may also be the sage (raise) driven from below connects with mission of troop units of any size. Mines an underground haulage level. The ore slides provide concealment and cover, but their use down this passage into the haulage level for removal. as shelter for troops may be hazardous and is seldom practicable. Most mines will not with- e. Military Considerations.The ability of any stand the effects of heavy surface bombard- nation to support a war depends upon its miner- ment. Coal mines are especially unsuitable for al resources and enemy mines are accordingly troops or storage. Coal is structurally unstable 103 and requires extensive supports even in ordi- i. Access road and turn around availability. nary mining operations. Many varieties of coal give off a gas known as fire damp or marsh gas. 111. Quarries and Pits This is highly flammable and highly explosive a. Quarries. A quarry is a site providing rock when mixed with air. Coal dust and air also that is suitable in quality, quantity, and size form an explosive mixture. Some mines, for construction purposes. A hardrock quarry particularly salt mines, may be utilized for the furnishes rock such as granite, limestone, or storage of supplies and equipment. Adit mines, sandstone, which must be drilled and blasted with their horizontal or slightly inclined en- in quarrying and which must be crushed for tries, are more suitable than vertical-shaft some uses. Igneous and metamorphic rocks are mines for underground storage. The latter type generally considered hard rocks. A soft-rock may present drainage problems and offers more quarry furnishes material that can be removed difficulties in transporting loads into and out readily by earthmoving equipment. Soft coral, of the mine. To prevent their use by the enemy, caliche, shale, chalk, and tuff are materials mines can be flooded or destroyed with ex- of this type. Sedimentary rocks are generally plosives. The possibility of mines being used considered soft. Quarries are generally the as headquarters for guerrillas must be con- open-faced type, with the vertical surface of sidered, and inactive mines in a tactical area the rock exposed. Depending upon local condi- should be blocked, destroyed, or otherwise tions, they may be developed by the single or secured against occupancy. multiple bench method. A single-bench quarry has the entire floor on one level, the height of Mines 110. Information Requirements - the bench worked in one operation varying The information about a mine required for from 2 to 30 meters (8 to 100 feet). A multiple- a terrain study will depend upon the purpose. bench quarry is one having a series of ledges Such information as the following usually is or terraces resembling steps. required: b. Pits. A pit is a site where earth or rock a. Location and name of mine. particles suitable for engineer construction b. Product (Mineral extracted, quality, may be obtained in quantity. A borrow pit is quantity, underground and in reserves). a site providing soil suitable for fills, surfacing, or blending that can be removed with earth- c. Extraction methods (deep, placer, strip, moving equipment. A gravel pit consists pre- special methods). dominantly of particles of gravel size. Unsort- d. Details of layout and operation. ed gravel from pits is used extensively for surfacing secondary roads, in base courses for (1) Pits, shafts, galleries, wells. pavements for roads, taxiways, and runways, (2) Hand and mechanical labor involved. and as aggregate in concrete and bituminous (3) Above ground structures, plant, and operations. An alluvial gravel pit derives its equipment. name from the origin of the deposit, since the material is stream-deposited. The gravel (4) Refining processes. obtained from these pits usually is very clean (5) Storage facilities. and free from clay and humus. It is therefore (6) Transportation facilities. particularly desirable for concrete and bituminous work. A bank or hill gravel pit pro- (7) Utilities (ventilation, electric power, duces a clayey gravel or clayey sandy gravel. lighting, water, firefighting). These materials are very desirable for surfac- e. Physical condition of installations and ing work because of their binding qualities. equipment. c. Military Considerations.Pits and quarries f. Safety and security features. are important chiefly as sources of materials for engineering construction. They may be local g. Availability of labor. objectives in tactical operations, if plans re- h. Any major repairs needed for operation. quire extensive engineering development of

104 the area. Individual pits and quarries usually the manner of loading, number of can be bypassed by advancing forces, but an trucks that can be loaded at one time, area containing a number of them may present access road, and turnarounds. difficulties to the movement of larger units and b. Pits. will tend to analyze movements. Flooded quarries are a particularly hazardous obstacle. Pits (1) Location. and quarries provide a varying degree of cover (2) Nature of source. for troops. They may also furnish defiladed locations for artillery and missile positions. (3) Nature of raw materials; quality, quantity. 112. Information Requirements -Quarries (4) Amount, depth, and type of over- and Pits burden. a. Quarries. (5) Drainage; ground-water level; stand- (1) Location. ing water. (2) Nature of stone. (6) Utilities available (electricity, water). (3) Actual and potential capacity in un- crushed stone. (7) Equipment available. (4) Capacity of crushing machinery in (8) Method of extraction (hand labor, stone of various sizes. machinery, dredging). (5) Details of machinery. (9) Method of cleaning and sorting. (6) Loading facilities (10) Daily production capacity. (7) Amount of crushed stone that can be (11) Transportation routes; access roads; hauled away in a day, considering surfaces of roads.

Section V. AIRFIELDS

113. Size, Form, and Components (1) Landing strips. a. Description. Airfields range in size and (2) A system of hardstands and runways. function from short landing strips consisting (3) Warmup aprons close to one or both of little more than a cleared area suitable for ends of the runway. light liaison planes or helicopters to large per- (4) Operation facilities, including control manent air bases with many complex sup- tower and operations and briefing porting installations. The simplest form of op- rooms. erational airfield consists essentially of a runway, usually oriented in the direction of pre- (5) Fuel storage and dispensing facilities. vailing winds; one or more perimeter taxiways, (6) Ammunition storage facilities. with warmup aprons located where they join the ends of the runway; and hardstands to ac. (7) General supply storage facilities. commodate one or more groups of aircraft. The (8) Repair and maintenance facilities for runway may or may not be surfaced. In addi- aircraft, accessories, and automotive tion, there will be a minimum of other facili- vehicles. ties, such as access and service roads, fuel stor- (9) Roads, walkways, communications, age, ordnance storage, and a control tower. The firefighting unit, and other service particular characteristics will depend upon the facilities. type of aircraft that will use the field. (10) Security and safety installations. b. Tactical Airfield. A tactical airfield in a theater of operations includes the following 114. Terrain major elements: a. Location. The general location of a pro- 105 posed airfield is indicated by the Air Force corm- water are required in both the con- mander or the Army aviation officer, as ap- struction and operation of airfields. propriate, while the exact site is chosen in co- (11) Camouflage requirements. A desirable ordination with the engineer after a careful site is one that avoids identifying evaluation of the terrain. landmarks and affords cover for in- b. Selection. In selecting a site, the follow- stallations and aircraft at dispersed ing factors should be considered: locations. (1) Adequate dimensions to meet operat- 115. Information Requirements - Airfields ional requirements, with room for future expansion. Based on available reports and files, detailed studies of particular airfields in local areas will (2) Accessibility to supply routes and be prepared by intelligence personnel. Pertinent communication facilities. information to be included in a terrain study (3) Obstructions along flightways and should include the following: approaches, including critical topo- a. Location (map coordinates, elevation, dis- graphical features, such as high hills tance and direction from nearest city or town, or mountains. High tension wires, principal landmarks, name if any). roads, and railroads crossing the flight way near the runway are dangerous b. Category (emergency landing strip, re- mental and physical hazards to pilots. fueling and rearming strip, fighter field, bomber (4) Meteorological conditions (wind, rain- field, heliport, and civilian secondary airport). fall, fog, snow, frost action). c. Characteristics of site (type of terrain, Drainage. character of soils, special aspects of weather (5) and terrain differing from country-wide or re- (6) Topography. A site with favorable gional conditions). topography is one located on high ground with sufficient slope for d. Detailed layout (sketch) of runways, tax- natural cross drainage as well as long- iways, parking and service areas. itudinal drainage and a reasonably e. Runways. smooth surface requiring little earth- (1) Identification. moving. (2) Length of runway and overrun; ex- (7) Clearing, grubbing, and stripping re- tensibility. quired. A large open area surrounded by sufficient covered areas to conceal (3) Width of runway, overrun, shoulders. all activities is ideal. Ground cover (4) Type and depth of surfacing and base. in areas adjacent to the flight strip is (5) Type and adequacy of drainage especially desirable to provide natural (ditches, subsurface drains). concealment for parked aircraft, dumps, and bivouac and other instal- (6) Load capacity (in pounds, or kilo- lations. grams or aircraft type). (8) Soil characteristics. The type of soil (7) Gradient. determines the type of equipment re- (8) Present condition. quired for construction, drainage, effects of adverse weather, and the sub- f. Taxiways and parking (dimensions, type grade bearing capacity that can be ob- and depth of surface material and base, load tained. capacity, condition). (9) Availability of gravel, sand, coral, or g. Detailed description of operation area; other materials for excavation. improvements planned or under construction. (10) Water supply. Large quantities of h. Facilities. 106 (1) Buildings (type, material, dimen- (3) Rainfall (average by months; wet sions). seasons; intensity, duration, and fre- (2) Maintenance and repair(number and quency of rainfall). extent of buildings and numbers and (4) Other aspects (temperature varia- types of equipment used for airfield tions, storms, fog, and ground haze). maintenance. (5) Availability of local construction (3) Fueling (number and capacity of materials. tanks, above or below ground). (6) Water supply. (4) Electricity supply. (5) Water supply. (7) Clearing and grading required. (8) Drainage conditions and required im- i. Related transportation (railroad, road, provements. water; details about type, location, and ca- (9) Soil classification. pacities of transportation facilities available). (10) Flight obstructions. ]. Airfield construction sites. (11) Frost heaving, permafrost, flooding, (1) Topography. extremely strong winds bear directly (2) Wind (direction, intensity of pre- on airfield site construction and main- vailing wind; local peculiarities). tenance.

Section VI. WATER TERMINALS 116. Ports and estimated capacities. A large-scale am- Water terminals (ports) may range in size phibious operation may include a number of from beaches suitable only for landing craft separate secondary landings to secure beaches to giant complexes extending along many that are suitable for dispersed logistical ter- miles of coastline. They usually constitute key minals. terrain features and primary objectives in military operations. FM 55-51 gives detailed in- b. Evaluation. Information about estab- formation about the organization and opera- lished water terminals usually is contained in tions of water terminals. Normally, major terrain studies prepared at the highest eche- water terminals (fig. 49) are characterized lons, which form the basis for studies used in by deep harbors protected from storms and specific operations. The existing water terminals are evaluated as to their usefulness and free from ice in the winter months. The rail and road networks of the area usually extend their present physical condition. If an enemy- from the terminals inland to developed por- held terminal is to be used by friendly forces tions of the country. Large terminals are often after its seizure, particular attention is given surrounded by commercial, industrial, and to the essential structures and facilities that shipbuilding areas. should be spared from destruction, if practicable, during the preliminary bombardment 117. Military Significance and assault. a. Vulnerability. Large water terminals are 118. Information Requirements - Water highly vulnerable to attack by nuclear weap- Terminals ons. When the enemy has a nuclear weapon capability, logistical support is provided The information about a water terminal through a number of dispersed small termi- which is most essential in preparing a terrain nals, often little more than beaches developed study will depend upon the features that are to meet minimum requirements. Terrain stud- of the greatest concern in a specific operation. ies should include an evaluation of all suitable Detailed information requirements for water locations for such terminals, indicating their terminals are contained in FM 55-8. Informa- physical characteristics, relative usefulness, tion required may include- 107 Figure 49. Typical large water terminal (port). a. Name, location by map references and (5) Location and nature of anchorages. coordinates. (6) Underwater obstructions. b. General characteristics (open roadstead, (7) Pilotage information. partly inclosed bay, landlocked harbor, shel- f. Bridges regarded as shipping obstruc- tered area behind a barrier reef, and river). tions (location, type, horizontal and vertical c. Entrance and approach channels (con- clearances at mean low water). trolling depth, length, width). g. Hydrographic and weather conditions. d. Breakwaters (position, length, construc- h. Adjacent beaches usable by landing craft tion). (location, length, type, gradient, and accessi- e. Description of harbor. bility). (1) Type. i. Cargo-handling facilities. (2) Harbor and channel depths. (1) Wharves, piers, and quays (type, function, structural features, cargo- (3) Extent of silting. handling machinery, road and rail- (4) Nature and frequency of mainte- road connections, utilities, mooring nance dredging. facilities).

108 (2) Wet docks and semitidal basins. (5) Open storage (location of suitable (3) Mechanical handling facilities. areas, rail and road connections, approximate capacity). (4) Harbor-service craft (type, function, number). (6) Petroleum and coal storage (location, type, capacity, bunkering facilities). j. Repair facilities. (7) Special storage facilities for explo- (1) Repair yards. sives and ammunition. (2) Graving docks. 1. Clearance facilities (rail lines, highways, (3) Floating docks. inland waterways, pipe lines). (4) Marine railways. m. Water supply (availability, quality, k. Storage facilities. method and rate of supply). (1) Location, type of commodities stored, n. Electric power and lighting (availability, type of constructions, capacity, trans- source, and characteristics of current). portation connections, fire protection, o. Capacity of the terminal as a whole, under special handling equipment. both normal and present conditions. (2) Cold storage facilities (temperature, p. Data needed for major repairs and im- daily ice making capacity). provements; vacant areas available for ex- (3) Grain storage facilities. pansion. (4) Bulk liquid storage (capacities in q. Availability of trained, reliable person- barrels). nel.

Section VII. HYDRAULIC STRUCTURES

119. Types made of stone masonry or concrete. They are a. Flood Control. The principal structure built either straight across the river or in the employed in flood control is the artificial levee, form of an arc, the convex side fronting the an embankment built along a river course to stream (fig. 50). prevent flooding of the adjacent country dur- c. Reservoirs. A reservoir is a wholly or ing high water. It may be 6 meters (20 feet) partly artificial lake used for water storage. or more in height, and usually is made by Types of reservoirs include those for flood con- packing layers of earth upon a foundation, trol, irrigation, recreation, power production, with grass planted on top of the levee to hold and navigation. Reservoirs are utilized for the soil. The levee may be faced with concrete. municipal water supply systems, on rivers to Usually an artificial levee is constructed some aid in flood control, on canals to maintain the feet in rear of the river banks to provide a water level for navigation, and in hydroelec- wider channel during flood periods. tric installations to insure a constant water supply. The reservoir may have a lining of b. Dams. Earth dams for reservoirs fre- clay or other impervious material to prevent quently are built of layers of homogeneous ma- water seepage. The embankments or retaining terial with a center core of puddled clay or walls may be of earth, loose rock, or masonry. other impermeable material. Usually the inner Distributing reservoirs in municipal water sys- surface is paved with stone or concrete as a tems sometimes are built of masonry or rein- precaution against erosion, and the outer sur- forced concrete. They serve to take care of face is covered with grass to bind the surface fluctuations in demand and as a reserve in case and to protect it against the weather. Dams of interruptions at the source. In reservoirs across rivers and deep ravines, or where there with earth embankments, overflow is provided is considerable width and height, usually are for by a waste weir or canal, to carry off sur-

109 Figure 50. Downstream face of Shasta Dam (California). plus water. When the reservoir is formed by a vessel goes from a higher to a lower level. masonry dam across a river, the surplus water Many locks have an intermediate set of gates may be allowed to flow over the top, or spill- so that only part of the lock is used for smaller ways may be provided (fig. 51). vessels. Usually the water passes through culverts built into the lock walls and is con- d. Locks. The dominant feature of developed trolled by sluice gates powered by hydraulic waterways is the canal lock. A lock is an en- or electric power. Lock gates are made of closed stretch of water with a gate at each either steel or wood. A pair of gates meets in end used to raise or lower vessels from one the center of the lock entrance. When closed, water level to another. When a vessel is to pass the gates form an arc with the convex side from a low level to a higher one, the water in toward the pressure of the water. The lift of a the lock is lowered until it is level with that canal lock may be 12 meters (40 feet) or more. in which the ship is floating. The vessel is moved into the lock and the gate is closed. e. Polders. Areas with an extensive network Water is then allowed to enter the lock until of canals, drainage ditches, and levees may it reaches the higher level, and then the gate create a major problem in operations. The at the other end is opened and the vessel passes most notable of these areas are the polders of through. This procedure is reversed when the Belgium and The Netherlands, which have

110 Figure 51. Spillway, storage dam (Bartlett Dam, Arizona). been reclaimed from the sea by artificial the width and velocity of a stream so that cross- levees called dikes. The terrain is traversed by ing operations are impeded. Hydraulic struc- numerous canals and basins that drain the ex- tures in enemy territory may be destroyed by cess water and serve as navigation routes. The aerial bombardment so as to cause these effects, surplus water empties into the sea at low tide. so they may be seized by airborne forces be- In places where the water courses lead from the fore the enemy can demolish them. Hydraulic interior to the sea, they may be caused to over- structures are vulnerable to sabotage and guer- flow, creating a practically impassable obstacle rilla action. Those in territory under friendly to movement. In the interior, the polders control must be carefully guarded and subject greatly limit the landing areas suitable for air- to strict security precautions. borne and airmobile forces. When the dikes are destroyed, the cultivated areas are inundated. 121. Information Requirements - Hydraulic In these areas tanks and vehicles bog down, Structures there is no cover for infantry, and the water The type of information that is required is too shallow for boats. concerning a particular hydraulic structure will depend upon whether plans call for its 120. Military Importance defense, seizure, destruction, or reconstruction. The military importance of hydraulic struc- Usually technical specialists are employed to tures arises from the extensive flooding that prepare detailed studies of each structure that may be caused by their destruction. Vast areas is being considered. In general, basic informa- may be inundated by the destruction of a large tion includes- dam or the artificial levees along a major river. a. Location and name. Releasing the waters of even a small dam may b. Function: navigation, power, flood con- flood sections of roads and railways or increase trol, irrigation, water supply.

111 c. Construction features: design type, mate- e. Security requirements. rials, height, width, mechanical equipment, capacity. f. Effects of destruction upon the surround- d. Extent and nature of repairs necessary. ing area.

Section VIII. URBAN AREAS AND BUILDINGS

122. Urban Areas and semi-detached building areas are those where the buildings are spaced relatively close a. Description. An urban area is defined as a together, as they are in low- and middle-cost concentration of structures, facilities, and pop- housing areas. Isolated housing areas are ulation which forms the economic and cultural found on the approaches to towns and cities focus for some larger area. Usually the in- where individual or small groups of homes are habitants do not depend upon agricultural ac- located in the midst of large open areas. This tivities for their basic economy. A city or town is typical of the suburbs of the average city. may have a number of functions that make it significant. It may be primarily industrial, d. Functional Areas. Normally a city in- commercial, or recreational; the headquarters cludes separate areas largely devoted to one of government institutions; a port or railway type of use. The major functional areas may center; or the location of an important cul- be distinguished as follows: tural feature, such as a cathedral, university, (1) Industrial areas comprise a grouping or historical landmark. A large urban area of individual plants and loft build- usually has a metropolitan area that includes ings, with associated storage and various surrounding settlements or suburbs transportation facilities, devoted to whose daily economic and social life is con- manufacturing activities. nected with or influenced by the city. Intelli- gence concerning an urban area covers its gen- (2) Commercial areas are composed of a eral description and importance; physical char- concentration of retail and wholesale acteristics; external communication; services establishments, financial institutions, and utilities; and major industries, including office buildings, hotels, garages, public storage facilities. buildings, and light manufacturing plants. and geology b. Topography. The topography (3) Residential areas consist predomi- of the urban area and its environs are signifi- nantly of dwellings with interspersed cant elements in the terrain study. Topography shopping centers; churches; schools; exerts a major influence upon the size and pat- and fire, police, telephone, and power tern of the populated area; the location of ex- stations. ternal communications; the possibility of inundation or other natural disaster; and the (4) Transportation and storage areas defense that can be made against possible land, contain the terminal, transshipment, waterborne, and air attacks. The development storage and repair facilities and serv- pattern of an urban area is the physical adjust- ice buildings associated with general ment of the area to its topography, as influ- movement by rail, water, road, pipe- enced by past events, current economic forces, line, or railway. and social trends. (5) Governmental-institutional areas in- c. Construction. The elements comprising an clude the grounds, structures, and urban area may be classified according to the facilities related to governmental ad- predominant construction and function of the ministrative offices, hospitals, schools, buildings and other structures. Where no gaps colleges, homes for the aged or or- exist between buildings, as in the business phans, sanitariums, monasteries, districts of larger towns and cities, this is de- penal or research institutions and scribed as block type construction. Detached similar establishments which usually 112 form distinctive and generally exten- weapon positions because of the dust caused sive areas. by the impact of projectiles and explosive (6) Military areas contain structures and charges and the smoke from explosions and facilities for billeting, quartering, de- fires. fense, hospitalization, storage, and c. Increased Cover and Concealment. Weap- repair, which are devoted exclusively ons and troops may be concealed in built-up to military use. areas, and ample cover is usually available against small-arms fire. Cover from air and (7) Open areas comprise land not occu- artillery bombardment, however, is provided pied by buildings and not assigned to only in buildings of particularly substantial any industrial, transportation, busi- construction. ness or residential activity. Developed open areas include cultivated land, d. Movement. The mobility and maneuver- parks, recreation areas, and ceme- ability of infantry, artillery, and armor are teries. Undeveloped open areas in- greatly limited in built-up areas. Vehicular clude swamps, woods, beaches, and traffic is canalized, and extremely vulnerable other vacant land. to ambush and the close-range direct fires of enemy weapons. 123. Military Considerations e. Communications. It is difficult to maintain a. Use of Urban Area. The decision to by- efficient communications in built-up areas. pass or to seize and occupy an urban area de- Normally control must be decentralized to pends upon the mission of the unit concerned. small-unit commanders. Tall buildings and Cities and towns may be important objectives those with steel frames may interfere with because they represent centers of population, radio communication. Reliance usually must be transportation, manufacture, and supply. Port placed upon wire and foot messengers. cities and railroad centers are given a priority f. Attack. Detailed information concerning status as targets and objectives in both tactical the enemy, his defenses, the terrain surround- and strategical planning. Unless the mission ing the urban area that is under his control, requires otherwise, a city or town usually is and the layout of the built-up area is essential bypassed and isolated, since it is an obstacle to the commander in making plans and deci- that canalizes and impedes both attacking and sions for an attack. Particular emphasis is counterattacking forces. Urban areas are vul- placed upon determining the location of cov- nerable to destruction by air or artillery bom- ered approaches to the urban area, the location bardment and may be neutralized by chemical, of public utility plants and their security biological, or radiological contamination. Fires measures and the location and nature of all started by nuclear weapons or incendiaries obstacles. The objective of the attacking force may make them untenable. Combat within is to seize the entire urban area. Within the built-up areas is described in detail in FM area the objectives for individual units include 31-50. key installations such as railroad stations, telephone exchanges, and the public utility plants, b. Limited Observation and Fields of Fire. which are often organized as centers of enemy Because the opposing troops usually are close resistance. The attack on an urban area begins to each other, effective close support by artil- with the seizure or terrain features which dom- lery and combat aviation is limited. The avail- inate approaches to the city, followed by the able cover is rigid and set in straight lines, so seizure of buildings on the near edge that all movement in the open usually can be to reduce observed unless it is concealed by smoke, dust, or eliminate the defender's observation and direct fire upon the approaches. The last phase or darkness. Smoke may be used to provide is a systematic advance through the area until concealment, limit observation, and achieve de- it is fully secured. ception and surprise. In a built-up area, smoke remains effective longer than in open areas. It g. Defense. Urban areas favor the defense. is usually difficult to observe and locate enemy Whether or not a city or town is organized for 113 defense depends upon its size, relation to the (4) Landmarks (natural and manmade). general defensive position, and the amount of (5) Extent of built-up areas (present cover it offers for occupying forces. Cities, towns, and villages constructed of flammable boundaries, recent additions, probable future expansion). materials provide little protection and may become a hazard to the defender, and buildings (6) Functional areas. of solid masonry can be developed into well- c. Structures. fortified defensive positions or centers of resistance. Cellars, sewers, subway tunnels, thick (1) Characteristics of predominant types masonry walls, and reinforced concrete floors of buildings (height, number of stor- and roofs provide cover for the defender dur- ies, principal construction materials). ing heavy bombardments. A heavy aerial or (2) Structure density (ratio of roof cov- artillery bombardment of a city before an at- erage to gross ground area; as war- tack actually may serve to strengthen its de- ranted, ratio of roof coverage to fenses. The fallen rubble may give the defender ground area within each of the func- increased protection, and may make the streets tional areas). impassable for armor. (3) Principal buildings. 124. Information Requirements-Urban d. Susceptibility to Fire and Shock. Areas e. Damaged or Destroyed Areas (delinea- Information about an urban area requires tion and general character). the compilation of many factors, each devoted to a particular aspect of the area, such as the f. Significant Ethnic and Religious Group- transportation services, utilities, billeting fa- ings (delineation and general character of the cilities, or industries. A terrain study should areas occupied). include annotated maps, plans, and photo- g. Streets. graphs, with an accompanying text giving that which cannot be shown graphically. Informa- (1) Surface, condition, and pattern. tion that should be included under each cate- (2) Prevailing widths (to curb and build- gory is outlined below. The scope of the in- ing to building). formation that is presented is limited by the (3) Names and alinement of through purpose for which the study is being prepared. routes and principal streets. The text should include information in the following categories, as pertinent: (4) Location and characteristics of bridges, tunnels, and ferries. a. Description. (1) Name and location (geographic and h. External Communications. grid coordinates). (1) Roads. Identification of the roads that (2) Population (number and trend, sig- enter the urban area, the routes that nificant ethnic and religious seg- bypass it, and the road distances to ments). the nearest important town on each route should be shown on maps. In (3) Principal function (communications the text, the importance of the roads and industry). as avenues of movement to and from b. Physical Characteristics. the town should be discussed. Anno- (1) Topography and geology of area and tations on city maps should locate and environs. identify highway structures, ferries, (2) General cross-country movement of and road service facilities. environs. (2) Railways. Maps should show the rail- (3) Climate (mean temperatures and ways that enter or bypass the urban rainfall). area, with distances to the nearest 114 important towns. Text should discuss (2) Sewage disposal (sanitary, storm, in- the importance of the railways as dustrial waste). transportation arteries. Annotations (a) Collection methods (type, ade- on city maps should locate and iden- quacy). tify railway structures and crossings (b) Treatment plants (type, location). (bridges, tunnels, and ferries) and such railway structures as passenger (c) Disposal methods (including loca- and freight stations, yards and sid- tion of dumps or incinerating ings, repair shops, turntables, and plants). "y" track. (3) Garbage and trash disposal. (3) Inland waterways. Identification of (a) Collection methods. each navigable water route (river, (b) Treatment plants (type, location). lake or canal) which borders or (c) Disposal methods (including loca- passes through the urban area and tion of dumps, incinerators, and the waterway distance to the nearest processing plants producing ferti- upstream or downstream port should lizer). appear on maps. The importance of (4) Major hospitals. the waterway should be discussed in (a) Name, location, and specialization, the text. Annotations on city maps if any. should locate and identify important waterway structures. Information on (b) Bed capacity. shipyards is included with that on the (c) Age and condition. industries of the urban area. (5) Electricity. (4) Airfields. The location of each airfield (a) Sources (name, type, location, in- and seaplane station which serves the stalled capacity). urban area should be shown on city (b) Substations (name, type, location, maps or, if beyond the limits of the capacity). city, on topographic maps. Text (c) Distribution current characteris- should indicate the adequacy of the tics. existing air service, list each com- (d) Number of consumers. mercial airline which serves the area, and provide information on the fre- (e) Yearly consumption. quency of service. Information about (6) Gas. airfield classification is presented in (a) Type. TM 5-330. (b) Sources (name, location, capacity). i. Urban Services and Facilities. (c) Storage (type, location, capacity). (1) Water supply. (d) Extent of distribution. (a) Sources (name, location, type, ca- (e) Number of consumers. pacity). (f) Yearly consumption. (b) Treatment plants (number, type, (7) Storage. capacity, and location). (a) Open (large open areas within or (c) Storage (name, location, type, ca- adjoining the town suitable for use pacity). as open storage and supply dumps). (d) Method of distribution. (b) Covered (warehouses and sheds). (e) Consumption (in terms of mini- (c) Cold (refrigerated storage; ice mum and average requirements per plants with cold-storage facilities). person per day, whether any ra- (d) POL (number of tanks or reser- tioning is practiced and during voirs at each location; capacities in what periods, annual consumption). U. S. barrels). (e) Explosives (magazine and bulk- b. Military Considerations. The military sig- storage facilities; types and quan- nificance of a building or group of buildings tities of explosives stored). depends upon the purposes of the study. A (8) Ice-manufacturing plants (name, lo- building may have value as an obstacle, a de- cation, capacity). fensive strongpoint, or as a possible storage, headquarters, medical, or maintenance instal- (9) Billeting and accommodation. (Total lation. The structural features of buildings capacity for billeting and accommoda- comprise the predominant materials used, size tion in military barracks, hotels, pub- and height, fire resistance, and architectural lic buildings, school and institutional design. Brick, stone, and masonry buildings, buildings, and other structures; total when demolished, create rubble that may make capacity of bakery and laundry estab- formidable obstacles, or may provide conceal- lishments; availability of baths and ment and cover for troops. Flimsy wooden swimming pools suitable for troop buildings are highly flammable and may be use. Location, capacity, and type of remunerative targets for incendiary shells and each structure.) bombs. Since the fires are an obstacle to an at- (10) Internal transit system (type, extent, tacker, they may be employed as a weapon by location of main terminal, and main- the defender. The height and number of stories tenance facilities). in a building are significant features when (11) Fire protection (organization and selecting observation points. Buildings used in manpower of fire department; quan- the community may be adapted for military tity and type of equipment). uses. These include garages and other repair facilities, stadiums, theaters, auditoriums, (12) City government (type, personalities, warehouses, transportation terminals, and location of facilities). schools. Wherever possible, structures of re- (13) Civil defense (organization and man- ligious or artistic importance are usually desig- power; quantity and type of equip- nated before an operation by civil affairs/mili- ment). tary government agencies, and their employ- (14) Industry. ment for military purposes is prohibited. (a) Major industrial activity (for each Buildings made of solid masonry, concrete, and industry, the type, number of steel may be organized into defensive strong- plants, number of employees, and points. Substantial structures with deep base- importance) . ments provide varying degrees of cover from air or artillery attack. The protection against (b) Significant manufacturing plants. nuclear effects offered by buildings varies ac- 125. Buildings cording to the type of construction, flamma- bility, distance from ground zero, and many a. Construction. The design and construc- other factors. Personnel in buildings will be tion of buildings are influenced by climate, protected from the thermal radiation effects available materials, function, and the cultural of a nuclear weapon and will receive some de- development of the native inhabitants. In areas gree of protection from nuclear radiation with a tropical climate and primitive agricul- effects. Casualties from secondary blast effects ture, for example, buildings usually are only are caused largely by falling walls and ceil- crude huts made of woven grass, sticks, and ings and flying glass. mud. Buildings in desert oases are made of clay with thick walls, so that they are cool in 126. Information Requirements-Buildings summer and fairly warm in winter. In dry climates, where suitable timber is scarce, a a. Location and function (residence, store, wooden structure is a rarity and buildings are warehouse, factory, school, government head- constructed from stone, adobe clay, or turf. quarters, and communication center). Where there are cold winters, buildings will be solidly constructed of stone and wood. b. Structural features (materials, founda- 116 tions, roof, bearing capacity of floors, exits, and the amount of military equipment that and basement). must be provided to supplement the existing utility installations. These studies also furnish c. Layout and capacity (floor plans, areas, a guide to selecting the most profitable targets cubages). for air attack. The destruction of key utilities d. Utilities. is given a high priority in planning aerial bombardments, since a breakdown in these e. Possible military uses. services results in disorganization of the en- f. Security features (estimated capability emy defenses and is highly damaging to civil- for withstanding bombardment by conven- ian morale. tional and nuclear weapons). 128. Information Requirements-Utilities g. Needed repairs or improvements for military use. The amount and type of information about the utilities of an urban area that is required 127. Utilities will depend upon the purpose for which the area is being considered. If it is intended to a. Special Studies. Detailed intelligence develop a city into a major logistical base, about the utilities of an urban area is neces- complete information concerning the capacity, sary in order to plan its utilization for mili- state of repair, and operating methods of each tary purposes. In addition, civil affairs may utility will be nceessary. The capability to sup- require specific, detailed information and in- ply minimum civilian needs as well as military telligence for special purposes. Special studies requirements must be evaluated. General sur- by technical personnel should be prepared cov- veys of utilities should include the following ering each of the following: information about each service or installa- (1) Water supply. tion- (2) Sewage disposal. a. Physical condition. (3) Electric power. (4) Illuminating gas. b. Adequacy for normal load. (5) Public transportation system c. Portion of present capacity that could be (6) Communications. diverted to military use. (7) Fire protection. d. Repairs, essential for military utilization. (8) Trash and garbage disposal. e. Safety and security provisions. b. Use of Special Studies. Intelligence stud- f. Availability of skilled, reliable, civilian ies covering utilities form the basis for esti- personnel. mating requirements for operating and maintenance personnel, the equipment and replace- g. General efficiency and dependability of ment parts needed for repairs and operation, the plant or system.

Section IX. NONURBAN AREAS 129. Types mates, most of the inhabitants dwell along streams and waterways, the settlements being a. Farmstead. Populated areas outside towns and cities usually consist of farmsteads and located on the bluffs, which are well-drained small settlements. A farmstead is the dwelling and exposed to the river breezes. The large rubber, coconut, or banana plantations are usu- and adjacent buildings associated with an in- ally near the ocean or on the banks of naviga- dividual farm. The characteristics of a farm- ble rivers, since roads and railways are few stead reflect the climate of the area and the and difficult to maintain. Nonurban areas in type of agriculture. dry subtropical climates are dominated by b. Tropical Climate. In rainy tropical cli- large cattle and sheep ranches, with individ-

117 ual farmsteads separated by miles of grazing quarters and other facilities for large numbers land. In semiarid tropical climates, the native of troops. agriculture is largely pastoral, and the rela- b. In tactical operations, it is occasionally tively few settlements consists of huts sur- necessary to secure or destroy small villages rounded by mud walls or fences of thorny that have no direct military value but are used brush. Subarctic villages seldom consist of to provide concealment, supplies, and other more than a dozen dwellings, with as much as support to guerrillas. The civilian inhabitants 50 to 65 kilometers (30 to 40 miles) between may have to be relocated in other settlements settled areas. under military control. The buildings of a c. Temperate Climate. In temperate climates, farmstead furnish quarters for troops and the buildings of a farmstead are detached from shelter for storage and maintenance facilities. each other, while in areas with extremely cold Stone buildings may be suitable for weapons winters the house, barn, and other outbuildings emplacements and defensive strongpoints. commonly are under one roof. The outbuildings Nearly all rural dwellings are within a short of a farmstead in the tropics normally are few distance of a reliable source of water. Cross- and small, because the animals remain out- country movement frequently is hampered by doors all year. Small villages in the middle obstacles such as stone fences, retaining walls, latitudes often consist of houses built in rows irrigation ditches, and paddy fields. Features along the sides of a road or clustered around such as high fences, hedgerows, embankments, an open square, and in tropical climates the and ditches may offer limited cover and con- houses of a village usually are dispersed with- cealment to individuals and small groups. out any regular pattern. 131. Information Requirements-Nonurban Areas 130. Military Significance The particular information about a farm- same considerations that a. In general, the stead or small village that is required will de- are pertinent to an urban area also apply to pend largely upon the mission of the unit nonurban areas. Small settlements may be concerned. Basic information requirements critical when they dominate routes of commu- should include- nication at fords, bridges, railway lines, or defiles (fig. 52). Villages that are small in a. Location; relation to local terrain fea- size may have considerable military signifi- tures. cance because of a particular industry, mine, b. Size (area, population, pattern of streets or other unique economic feature. They may or roads). be local markets and distribution centers serv- ing a wide area and representing an important c. Facilities for quarters, maintenance and enemy source of foodstuffs and other supplies. repair installations. A village with a small local population may be d. Predominant construction materials. a resort area or the site of a university or similar large institution, capable of providing e. Utilities.

118 EL4A"II:

119 CHAPTER 7

MILITARY ASPECTS OF THE TERRAIN

Section I. MILITARY USE OF TERRAIN

132. Commander's Considerations boundaries, into subareas based upon the tactical plan. The military aspects of the terrain In conducting an operation, the commander then are evaluated by each subarea from both must determine how the terrain can be used the friendly and enemy points of view. most effectively by his forces, how it may affect the enemy's capabilities, and how it may be exploited to interfere with the enemy. With 134. Observation and Fields of Fire the assistance of his staff, he considers the a. Observation. Observation is the direct ex- weather conditions, relief and drainage, vege- amination of terrain and military activities. tation, surface materials, and manmade fea- It includes examination from ground and air tures and their effects upon- by unaided vision or assisted by optical and a. Key terrain. infrared devices and detection by photographs, radar, and sonic devices. In general, observa- b. Observation and fields of fire. tion refers to the ability of a force to see the c. Cover and concealment. enemy under specified conditions of weather and terrain. The best terrain for observation d. Obstacles. is that which permits both long-range observa- e. Avenues of approach. tion into enemy-held areas and close-in observation of the hostile forward elements. f. Communications. Usually long-range observation is found near the topographical crest and close-in observa- 133. Key Terrain tion is obtained from a location near the mili- The relative importance of various aspects tary crest. Fog, smoke, precipitation, heat of the terrain varies with the mission, the type refraction, darkness, manmade and natural of operation, the size and composition of the features, and vegetation may limit or deny forces involved, and their weapons and equip- observation. They must be evaluated in deter- ment. Detailed intelligence concerning terrain mining the extent and type of observation that features normally increases as the size of the will be available to enemy and friendly forces. unit diminishes. The commander of a field The highest point on the terrain does not al- army, for example, may be concerned about ways provide the best observation, since varia- the effects that an extensive mountain range tions in relief often create blind spots in the will have upon a proposed campaign. A corps field of vision. The selection of observation commander might be interested only in one points should be based upon reconnaissance, mountain of the range, while the commander topographic profiles, or examination of aerial of a brigade would concentrate upon a particu- photographs. lar group of foothills in his area. When making a systematic study of the military aspects of b. Fields of Fire. A field of fire is an area an area, it is sometimes divided into natural that a weapon or group of weapons can cover subareas, or, if there are no suitable natural effectively with fire from a given position. The 120 natural terrain must be evaluated according difficult to obtain. Caves, buildings of excep- to its suitability for flat-trajectory weapons, tionally strong construction, and the steep high-trajectory weapons, rockets, and guided slopes of hills and mountains may offer some missiles, including those with nuclear capabil- degree of cover, depending upon the capabili- ities. The ideal field of fire for flat-trajectory ties of the weapons employed by the enemy. weapons is flat or gently sloping terrain on Nuclear thermal radiation travels by line of which an enemy can be seen with no protec- sight, so that it will be masked by hills, banks tion for him within the effective ranges of the of ravines, and gullies. The extent of protec- waepons. Broken terrain creates dead spots tion thus provided will depend upon the and furnishes cover and concealment for the height of the explosion. A nuclear blast wave enemy. Open terrain providing good fields of curves around obstacles and is less affected by fire permits a unit to defend a wide front. relief features. Broken terrain makes it necessary to provide more troops and weapons to defend a given c. Concealment. Terrain features that offer frontage. The field of fire of high-trajectory cover also provide concealment. The greater weapons is limited only by very steep reverse the irregularity of the terrain, the more con- slopes that the weapons cannot reach and by cealment it will furnish from ground observa- masks which permit the enemy to occupy position. Lower echelons are concerned with the tions in defilade. Fields of fire can be improved concealment of men, vehicles, weapons, and by cutting or burning vegetation, demolishing emplacements; higher echelons, with the con- buildings, and cutting lanes through woods. cealment of headquarters, supply dumps, airfields, and other major installations. 135. Cover and Concealment 136. Obstacles a. Evaluation of Terrain. Terrain is evaluated to insure the maximum use of conceal- a. Types. According to their effects, obsta- ment and cover. Terrain under enemy control cles may be classified as antipersonnel obsta- is also studied, to determine how his conceal- cles, antimechanized obstacles, underwater ment and cover can be destroyed. In the attack, obstacles, and obstacles to the landing of air- concealed and covered routes into the enemy craft. Natural obstacles comprise such fea- position are sought to gain surprise and to tures as unfordable streams, swamps, deep reduce casualties. In the defense, concealment snow, cliffs, steep slopes, thick woods and un- and cover are utilized not only to protect in- dergrowth, flooded areas, boulder-strewn areas, dividual positions, but also to hide the general lakes, mountains, and nontrafficable soils. Arti- trace of the defenses, so that the attacking ficial obstacles include those prepared to delay troops may be vulnerable to surprise by the or stop military movement, such as contami- location of defense positions and weapons nated areas, minefields, trenches, antitank fires. When evaluating terrain for the cover ditches or barriers, roadblocks, blown bridges, that it will provide, the characteristics of all road craters, deliberately flooded areas, wire the weapons used by the enemy must be con- entanglements, and various types of beach and sidered. This includes their ranges, types of underwater obstacles. They also include man- fire, and the relative quantities of each type of made features that were not originally de- weapon available to him. signed as obstacles to military movement, such as canals, levees, quarries, or reservoirs. b. Cover. Topography is the major factor influencing cover. Valleys, mountains, gullies, b. Employment. The employment of obsta- ravines, hills, and similar features provide cles is integrated with the overall scheme of cover from flat-trajectory weapons. Individuals maneuver and fire support. Both natural and and small units may secure cover from such artificial obstacles are utilized to channel, di- terrain features as ditches, riverbanks, folds rect, restrict, delay, or stop an opposing force. in the ground, shell craters, buildings, walls, Instructions for the employment of obstacles railroad embankments and cuts, and highway usually are included as a barrier annex to the fills. Cover from high-angle weapons usually is operation order of divisions or higher echelons. 121 FM 31-10 discusses the use of obstacles and and nature. For example, a deep creek lying the requirements of barrier plans. across the axis of advance will slow up an c. Barriers. A barrier plan provides for the attacker, but will provide defending forces most effective employment of obstacles to im- with an advantage, since it delays advancing pede enemy movement along favorable routes troops and exposes them to fire. Similarly, of approach, divert advancing enemy forces heavy woods in front of a position may pro- towards routes favorable to defense or compel vide infantry with a concealed route of ap- the enemy to concentrate or disperse. Artificial proach but act as an obstacle to the movement obstacles must not be located where they of supporting tanks. In general, obstacles per- would interfere with the proposed movements pendicular to the axis of advance favor a de- of friendly forces or with counterattack plans. fending force, while those parallel to the axis They may be placed in considerable depth, so may give the attacker an advantage by protect- ing his flanks, although they will also limit as to provide time for counterattacking troops to meet an enemy threat, and to force the lateral movement and his ability to maneuver. enemy to expend time and strength at each f. Offense. In offensive operations, obstacles barrier. To be fully effective, artificial obsta- influence the choice of objectives, the avenues cles must be kept under observation at all of approach to an objective, and the time and times, and must be augmented by fire or ex- formation of an attack. Obstacles may be em- plosives. Whenever possible, obstacles are sited ployed to contribute to flank security, impede so that they are under friendly observation but counterattack, provide additional protection defiladed from enemy observation. Local unit for a section of the front that is not strongly commanders are responsible for constructing manned, or assist in enemy entrapment. obstacles for the close-in defense of their posi- g. Defense. Obstacles are employed in the tions. Advice and technical assistance is pro- defense to channel, direct, delay, or stop the vided by engineers, who also construct and movement of an approaching force. They may install obstacles which require special skill and be used to delay the initial enemy advance equipment. The use of toxic chemical and bio- toward the front and flanks of a position, de- logical agents and radiological contamination lay the movements of enemy penetrating or to supplement barriers or as obstacles, makes enveloping forces, or canalize enemy penetra- it possible to deny or restrict areas by con- tions into avenues of approach where they can tamination, to canalize enemy maneuver, or to be defeated, or destroyed. contaminate enemy field fortifications so that they are untenable. Additional information 137. Avenues of Approach about the employment of these agents is contained in FM 3-5, FM 21-40, and FM 100-5. a. To a Terrain Feature or an Objective. This is an area of terrain which provides a d. Effects. The effects of natural terrain suitable, relatively easy route of movement for features as obstacles to military movement are a force of a particular size and type. An ave- discussed in chapter 6. Artificial obstacles are nue of approach should provide- described in FM 5-15 and FM 31-10. The location and extent of both natural and arti- (1) Ease of movement toward the objec- ficial obstacles must be considered by a com- tive. mander in making his plans. He must decide (2) Concealment and cover from the de- how they will affect his mission. The tactical fender's observation and fire. effect of an obstacle depends upon the type of (3) Favorable observation and fields of operation, the weapons and equipment em- fire for the attacker. ployed, and the size of the forces involved. A terrain feature that is a major obstacle for a (4) Adequate maneuver room for the at- company may be a minor obstacle to a brigade tacking force. and no obstacle at all to a division. b. Suitability and Ease of Movement. The e. Location. Obstacles may either help or suitability and ease of movement of an avenue hinder a unit, depending upon their location of approach depend upon- 122 (1) The routes of communication. area bounded on at least two opposite sides by (2) Soil trafficability. terrain features such as woods, ridges, or vil- (3) Concealment and cover. lages that limit observation and observed fire (4) Observation and fields of fire. into the area from points outside the area. A (5) Obstacles. terrain compartment includes not only the area (6) Relationship of terrain corridors and enclosed but the limiting features as well. De- cross compartments. limiting lines are imaginary lines drawn along limiting features from which ground observe- c. Multiple Use. In some types of operations, tion into a compartment is limited. In in which compart- maneuver is very limited by either ments formed by woods and villages, these weather or terrain, an avenue of approach may lines run at some point within in itself the edge of the be a key terrain feature. For example, woods or village, depending upon the density in rugged mountainous terrain, one road along of the woods, or the number a valley and density of the may be the only route of supply and at buildings. Compartments the same are classified accord- time thb most favorable avenue for ing to the direction of movement approach for the of the forces major element of the attack- operating in them. They are termed ing force. A river in the jungle corridors may be the (fig. 53) when the longer dimension of the only transportation route, and thus a key ter- compartment lies generally in the direction of rain feature, an avenue of approach, and an movement, obstacle. or leads toward the objective, and cross compartments (fig. 54) when the longer d. In Attack. Usually an attack is directed axis is perpendicular or oblique to the direc- toward securing dominating terrain early in tion of movement. Compartments are also the action. The avenue of approach that is classified as simple or complex (figs. 55 and most favorable for accomplishing this mission 56). A complex compartment is one having a normally is assigned to the forces making the smaller compartment or compartments lying main attack. Whenever possible, the avenues within it. This is the type most often encoun- of approach that are selected are those that tered. avoid areas most strongly held by the enemy. In planning an attack, a study is made of the 139. Corridors avenues of approach that might be used by the Corridors, or ridges that form their limiting enemy for counterattacks and for reinforcing features, provide favorable routes of approach and supplying his forces. These avenues can be for an advancing force because the defender's determined by an analysis of the terrain in its lateral organization and fields of flat-trajectory relation to the location of enemy reserves and fire are obstructed by the limiting features, supply routes. which also decrease his ability to obtain mu- e. In Defense. In planning the organization of tual support between units and limit his obser- defense positions, the terrain is evaluated to vation. To the attacker, a corridor offers two determine the avenues of approach that are types of approach: valley approach and ridge most likely to be used by the enemy. These approach. normally will be the avenues that lead toward a. Valley Approach. Although a valley ap- key terrain features, provide good observation, proach may provide concealment and cover, fields of fire, concealment and cover, and either the military crest of the limiting features on avoid or exploit obstacles. Defense positions are each side must be controlled to deny enemy sited to deny such avenues of approach to the observation and direct fire into the valley. The enemy. The avenues of approach that can be best axis of advance is the one that offers the used by friendly forces in counterattacks also most favorable conditions of observation, are evaluated. cross-country movement, fields of fire, concealment, and cover. 138. Compartments Often the most favorable route is along the slopes of a ridge below the The effects of relief and drainage upon ave- military crest rather than along the valley nues of approach are considered in terms of floor. A valley approach should never be used compartments. A terrain compartment is an when the enemy controls dominant flank ob- 123 Ait DIRECTION OF ATTACK Figure 53. Terrain corridor.

Figure 54. Cross compartmnent. 124 Figure 55. Simple compartment.

II II II II II II

Figure 56. Complex compartments. 125 servation into the valley, where there are slightly below the topographical crest, with numerous obstacles, and the soils have poor sufficient forces deployed to control the crest. trafficability characteristics. c. Cross Compartments. Cross compartments b. Ridge Approach. The suitability of a provide the defender with the most favorable ridge for an avenue of approach depends upon terrain for obtaining maximum observation its width and shape, the size and frontage of and fields of fire. Mutual support between the unit concerned, the distance to adjacent units, both laterally and in depth, is available ridges and their elevations, and the capabil- and cross compartments also provide the de- ities of the enemy weapons. A ridge approach fender with successive defensive or delaying places the axis of advance along dominant positions. The concealment or cover provided observation, but offers little protection from by each limiting feature permits the defender enemy fire directed at the ridge. Usually the to shift his reserves to meet or to counter best axis of advance in a ridge approach is threats to his position.

Section II. SPECIAL OPERATIONS 140. Amphibious Operations evaluated to determine those that come nearest a. Detailed Studies. Amphibious operations to the optimum requirements. require detailed studies of hydrography, d. Coastal Plain. A landing on a wide weather, and terrain. A technical discussion of coastal plain provides unrestricted maneuver the requirements and preparation of these room usually free from enemy observation studies is beyond the scope of this manual. and a subsequent advance from the beach can They are covered in FM 6030, FM 110-101, be made in any direction. Boundaries and ob- and FM 110-115, which also describe the char- jectives are hard to locate on this type of ter- acteristics, tactics, and techniques of amphib- rain, however, and there are few prominent ious operations. The discussion in this para- registration points for artillery, naval gunfire, graph supplements information in paragraphs and aerial bombardment. Usually there is no 70 through 75. good defensive terrain on the flanks of the b. Weather Effects. All phases of an amphib- beachhead, so that more troops are required to ious operation are directly influenced by protect the flanks. weather conditions. Weather affects the tides, e. Coastal Ridge. Terrain which rises evenly beaching and unloading conditions, speeds of to a considerable distance back from the beach vessels, air support, and visibility. Poor weath- gives the defender excellent observation and er conditions may provide cover for the am- fields of fire. More commonly, the coastal area phibious force, but favorable weather is essen- remains flat for some distance and then rises tial for the actual landing and during the abruptly to a coastal ridge. initial buildup that follows, because excessive f. Sand Dunes. Ground that is sharply sea and swell jeopardize the entire operation. broken by extensive sand dunes or a low c. Location. The ideal beach for an amphibi- coastal plateau provides the attacker with con- ous landing is one near a strategic location, cealment from enemy observation. The small with no obstructions seaward; deep water compartments and corridors limit the range of close nearshore; a firm bottom; minimum vari- defensive fires. Direction and control may be ation in tides, currents, or surf. The beach extremely difficult. terrain should be gently rising, relatively g. Mountains. Mountains located directly on clear, with a firm surface that has adequate the sea usually limit the number of beaches drainage. Adequate exits from the beach area large enough to accommodate a landing force of should be available. Flat or gently rising ter- effective size. Where steep ground is lightly rain, backed by a coastal range high enough defended or neglected by the enemy, a lightly to mask the landing area, is the most desirable equipped force may seize it and gain surprise. for landing operations. Ideal conditions are Airborne or airmobile troops may be used to rarely found, and so suitable areas must be block the movement of enemy reserves to the 126 landing area, or to secure passes through the tics can land in areas that are otherwise ac- mountains and thus prevent the enemy from cessible only to parachute units. interfering with the amphibious landing. c. Drop Areas. The selection of drop areas by parachute re- 141. Airborne-Airmobile Operations for the delivery of supplies quires a consideration of the following: tactics, a. Basic Factors. The characteristics, length of the and techniques of airborne operations are (1) Length. The required discussed in FM 17-36 and FM 57-10. Air- area depends upon the type of plane are capable of crossing such ter- being used. Normally an area 460 borne forces meters (500 yards) long is a mini- barriers as inland seas, mountains, and rain mum requirement. jungles that represent serious obstacles to the movement of other troops. Usually airborne as- (2) Width. A width of 180 meters (200 saults are made on terrain that is relatively yards) is minimum. The pilot must undefended, to secure initial surprise. Weather have a reasonable amount of room so has greater restrictive effects upon airborne that he may fly to the right or left of operations than upon ground operations. Ad- the center of the area, allowing for verse weather may cause postponement or de- the drift of his plane under the in- lay in initiating an operation, and prevent fluence of surface winds. adequate reinforcement or supply by air. In (3) Surface conditions. The type of soil addition to terrain studies covering landing must be considered in relation to the and drop-zone areas, special studies may be effect that it will have upon the fall- required to determine the most favorable ing loads. A hard surface may cause routes for linkup between airborne forces and the bundles to break open upon land- friendly ground units. ing. Soil that is muddy or swampy b. Terrain Requirements. One of the princi- may cause the dropped loads to bury pal factors influencing the selection of a land- themselves upon landing, making re- ing area for airborne forces is the terrain. The covery difficult or impossible. area chosen must provide adequate space to (4) Topography. A clear and level area permit defense in depth; room for maneuver; is desirable. Drop zones on a steep a safe landing for troops, supplies, and equip- slope or mountainside cause the bun- ment; and protection for critical installations. dles to scatter, tumble, and break Airborne troops can land on any terrain that open. A mountain or hill top usually is relatively free from obstacles. Unobstructed has turbulent winds that reduce drop areas are required for the landing and recov- accuracy and make the drift of bun- ery of heavy equipment dropped by parachute. dles unpredictable. Assault aircraft can land on any relatively (5) Access. A desirable drop zone has an level and unobstructed terrain that has suit- adjacent road, or terrain adjoining able trafficability. Other fixed-wing transport the area, that offers good access for aircraft require suitable airfields or prepared vehicles, so that the dropped supplies landing strips. Rotary-wing and other aircraft can be recovered and transported with vertical takeoff and landing characteris- conveniently.

Section III. WATER SUPPLY

142. Importance sources or to deny them to an enemy. All An adequate supply of water for drinking, feasible sources and methods for developing sanitation, construction, and vehicle operation them must be considered when making plans is one of the fundamental needs. In arid and for the water supply of troops and installa- semiarid regions, water supply affects plans tions. Development data are obtained from re- and operations. Entire campaigns in desert connaissance, map study, reports or runoff and lands may be conducted solely to secure water rainfall average, and geological surveys. Water 127 sources are located by a study of maps, aerial water than do those fed mainly by surface photographs, water resources data, and intelli- runoff. Water in large lakes generally is of gence reports, then verified by field reconnais- excellent quality, the purity increasing with sance if feasible. Detailed information con- the distance from shore. Very shallow lakes cerning water supply is contained in TM 5- and small ponds are usually polluted. 700. d. Site Requirements. The ease with which a water source can be developed, operated, and 143. Sources maintained is determined largely by the loca- a. Basic Considerations.Water may be ob- tion and the routes of communication. The tained from wells, streams, springs, lakes, and design of the collecting system and the diffi- municipal or other supplies that are already culties of development, operations, and main- developed. Water for permanent and semi- tenance are partially influenced by site condi- permanent installations also may be secured tions, topography, soils and vegetation. A from the distillation of sea water or the drain- military water point should be located as close age from building roofs. Investigations to select as possible to a main route without interfering a water source must consider the quantity and with traffic. An all-weather access road should quality of the water, and the conditions at the lead to the place of storage, with a turnaround proposed sites from which the water supply or separate exit, and an all-weather off-road would be secured. parking area for trucks waiting to be filled. In locating the water point, attention is given to b. Quantity. The quantity of water available concealment and cover, possible nearby targets in an area depends chiefly upon the climate. In which may attract enemy fire, drainage, road temperate and tropical regions with less than connections, condition of the banks and the 60 centimeters (25 inches) of annual precipi- bed tation, most if surface water is being drawn, and the streams become dry in drought means required to periods. develop the source. Exist- Streams usually flow throughout the ing water supply systems are used when care- year in temperate regions with more than 60 fully checked by engineers and medical centimeters (25 inches) of annual rainfall and authorities. in tropical Purification units may have to be regions where the rainfall exceeds installed. The possibility of contamination by 90 to 100 centimeters (35 to 40 inches). Sea- enemy agents also must be considered. sonal variations may reduce the flow of water below the required amount or result in water 144. Surface Water points being flooded by seasonal high water periods. The seasonal characteristics of water a. Regional Variations. Surface water sources are generally more accessible and ade- sources should be obtained from local inhabi- quate in tants. Terrain studies usually indicate alter- plains and plateaus than in moun- nate water tains. Large amounts of good quality water sources for use in case the primary normally sources dry up, become flooded, or cannot be can be obtained in coastal, valley, or used because of enemy action. alluvial and glacial plains. Although large quantities also can be secured in delta plains, c. Quality. Color, turbidity, odor, taste, min- the water may be brackish or salty. Supplies eral content, and contamination determine the of water are scarce and difficult to obtain on quality of water. TM 5-700 gives methods lacustrine, loess, volcanic, and karst plains. In for estimating these characteristics and de- the plains of arid regions, water usually cannot scribes the use of standard test kits. The qual- be obtained in the quantities required by a ity of water will vary according to the source modern army. Much of the water that is avail- and the season, the kind and amount of bac- able is highly mineralized. In the plains and teria present, and the presence of dissolved plateaus of humid tropical regions, surface matter or sediment. Streams in inhabited water is abundant, but it is generally polluted regions commonly are polluted, with the sedi- by bacteria and requires treatment. Perennial ment greatest during flood stages. Streams fed surface water supplies are difficult to obtain in by lakes and springs, with a uniform flow, are Arctic regions. In summer, water is abundant usually clear and vary less in the quality of but often polluted. In winter it can be obtained 128 from beneath the ice in the larger lakes and fans, glacial outwash plains, and alluvial streams, but its quality is poor because of a basins in mountainous regions. Areas of sedi- high organic content. mentary and permeable igneous rocks also may b. Springs and Seeps. There are two types of have fair to excellent aquifers, although they springs or seeps: those originating at the base do not usually provide as much ground water of steep slopes where the topography breaks as areas composed of unconsolidated materials. abruptly, and those caused by faulting. The Aquifers of this type underlie coastal plains, first type is found along the edges of a valley, inland sedimentary plains and basins, karst and has a perennial flow and fresh, cold water. and volcanic plains and plateaus. Large The second type is caused by the fracture or amounts of good-quality ground water may be displacement of confining clay or rock layers obtained at shallow depths from the alluvial above an artesian water-bearing formation plains of valleys and coasts, and in somewhat (aquifer), thus forcing the water in the ar- greater depths in their terraces. Large quan- tesian zone to the surface. Springs of this type tities may also be secured from shallow wells often are thermal, and may contain excessive in delta plains, although it is apt to be brackish amounts of minerals. Frequently the depth of or salty. Aquifers underlying the surface of a source of water can be estimated by the inland sedimentary plains and basins also pro- temperature of the water; the hotter the vide adequate amounts of water. Often these water, the deeper the source. Spring water is formations lie with a few hundred feet of generally clear, cool, and low in organic im- the surface. Those at greater depths yield very purities, but may be hard because of a high hard water which may be too highly mineral- dissolved mineral content. In regions where sea- ized to be drinkable. Abundant quantities of sonal rainfall varies greatly, the spring flow good-quality water generally can be obtained often decreases during long periods of dry from shallow to deep wells in glacial plains. In weather. The heavy infiltration of surface loess plains and plateaus, small amounts of water causes some springs to become turbid, water may be secured from shallow wells, but and may produce contamination. these supplies are apt to fluctuate seasonally. c. Streams. Streams are the most common Water from wells usually is clear and low in source of surface water supply. Streamflow organic impurity, but it may be high in dis- may vary with precipitation, temperature, and solved mineral content. the amount of vegetation. Turbidity and min- b. Plains. Large springs are the best sources eral content vary with the flow and with of water in karst plains and plateaus. Wells watershed conditions. Since large flows pro- may produce large amounts if they tap under- duce high dilution, many such streams may be ground streams. To estimate the possible yield suitable sources of water supply although they of proposed wells, information is sought about receive raw or partially treated sewage. How- existing wells that tap similar water-bearing ever, water from such streams must be settled, formations in the vicinity. The siting and filtered, and chlorinated before use. drilling of wells is difficult because the areas of d. Lakes. Ordinarily, lakes are a satisfactory permeability and the solution cavities in lime- source of water supply. The water level and stone cannot be easily predicted. Shallow wells average yield in small lakes may vary. Many in low-lying lava plains normally produce large lakes receive sewage flow, have a high content quantities of ground water. In lava uplands, of dissolved minerals, and may have consider- where water is more difficult to find and wells able vegetative growth or contain vegetable or are harder to develop, careful prospecting is animal organisms. These can usually be re- necessary to obtain adequate supplies. In wells moved by purification processes. near the seacoast, excessive withdrawal of fresh water may lower the water table, allow- 145. Ground Water ing infiltration of salt water which ruins the a. Source. Ground water is obtained without well and the surrounding aquifer. Springs and difficulty from unconsolidated or poorly con- wells near the base of volcanic cones may yield solidated materials in alluvial valleys and fair quantities of water, but elsewhere in vol- plains, streams and coastal terraces, alluvial canic cones the ground water is too far below 129 the surface for drilling to be practicable. (2) Direct pumping. In direct pumping c. Climate. Plains and plateaus in arid cli- systems, ordinarily there are no ele- mates generally yield small, highly mineral- vated storage tanks. The water is ized quantities of ground water. In semiarid pumped into the distribution system climates, following a severe drought, there from ground storage reservoirs or frequently is a flow of subsurface water under wells at a rate depending on demand. an apparently dry streambed that may yield (3) Combination. Primary mains are sup- considerable amounts of excellent water. plied by both gravity and direct Ground water is abundant in the plains of pumping in combination systems. humid tropical regions, but usually it is pol- b. Parts. The essential parts of a water sup- luted by bacteria. In arctic and subarctic ply system are- plains, wells and springs fed by ground water (1) Headworks, usually a reservoir above the permafrost are dependable only in formed by a dam. summer; some of the sources freeze in winter, (2) Conduit, sometimes an open canal or and subterranean channels and outlets may an aqueduct, but more commonly shift in location during the seasons. Wells that made of wood, iron, or steel that is penetrate aquifers within or below the perma- watertight to prevent contamination frost, however, are good sources of perennial and losses by evaporation, absorp- supply. tion, and changes in temperature. d. Hills. Adequate supplies of ground water (3) Distributing system, which connects are hard to obtain in hills and mountains com- with the plumbing in buildings. Large posed of gneiss, granite, and granitelike rocks. mains carry the water from the They may contain springs and shallow wells source to service pipes, which take it that will yield water in small amounts. to individual buildings and other out- e. Military Use. Both large- and small-diam- lets. eter wells are used for military installations. 147. Information Requirements - Water Large-diameter wells usually are dug by hand, Supply in diameters up to 15 meters (50 feet). They may be used as reservoirs, the water level fall- Special water supply studies are made by en- ing during periods of withdrawal and being gineers, assisted by geologists and hydrologists. replenished from subterranean flow during The information required in terrain intelli- periods of light demand. Small-diameter wells, gence studies includes the following- normally, made by driving, jetting, boring, or a. General. drilling, do not provide storage. Deep wells are (1) Normal level of water table and vari- drilled by percussion rigs or rotary equipment. ations. The amount of water obtained from deep wells (2) Yield of springs and wells, and vari- will depend upon local conditions. They are less ations. subject than shallow wells to seasonal fluctua- (3) Potability and contaminations. tion, contamination, and pollution. Information (4) Underground flow in dry water- about wells and well-drilling is in TM 5-297. courses. b. Surface Supplies. 146. Water Supply Systems (1) Total drainage area. a. Types. There are 3 basic types of water (2) Rainfall and runoff data. supply and distribution systems- (3) 'Sources and kinds of possible con- (1) Gravity. The storage reservoirs of tamination, including sewage or in- gravity distribution systems usually dustrial wastes. are located high enough to develop (4) Chemical and bacteriological analy- the required pressure and flow. Some- ses. times the storage tanks are filled by c. Wells. gravity from springs located at a (1) Rainfall data. higher level, but ordinarily they are (2) Reports of available well logs and filled by pumps. test data.

130 (3) Physical, chemical, and bacteriolog- (3) Treatment methods. ical analyses. (4) Distance from supply to proposed military user point. d. Existing Water Supply System. (5) Pressures. (1) Source of supply. (6) Chemical and bacteriological analy- (2) Quantity provided; ultimate capacity. ses.

131 CHAPTER 8 TERRAIN STUDIES

Section I. BASIC FEATURES 148. Description (12) Airborne landing areas. a. Preparation.A terrain study is an intelli- (13) Soils. gence product which presents an analysis and (14) Rock types. interpretation of the natural and manmade (15) Drainage. characteristics of an area and their effects on (16) Climate. military operations. It is a compilation of only (17) Surface configuration. that information which has a direct bearing (18) Inland waterways. on some existing requirement. This study is (19) Other military aspects. prepared at all echelons to provide the intelli- 149. Prerequisite Information gence officer with an analysis of the terrain for use in preparing the analysis of area of Before initiating the study, one must know operations that forms part of his overall intelli- the area to be covered, the mission and type gence estimate for the commander, and for use of operation, the specific information required, by other staff elements for planning and con- and the time period to be considered. Terrain duct of operations. The preparation of an intelligence is produced continuously at all analysis of area of operations is discussed in echelons. The preparing unit maintains a file FM 30-5. Above army level, terrain studies of intelligence data, drawing upon it for per- are prepared primarily, to assist the com- tinent matter when he is directed to make a mander and his staff. At lower levels, terrain terrain study. Additional information is ob- studies are intended chiefly for use in tactical tained from the sources and agencies discussed operations and include more details of the ter- in chapter 3. rain and its effects. 150. Format b. Topics. Special studies devoted exclusive- a. Content. A specific ly to certain terrain features or effects may be terrain study will not cover every item prepared to meet the requirements of a parti- in outline, but only those cular plan or operation. These are produced by items applicable to the operation being planned. Used in this manner, technical personnel or teams, and include, but the terrain study form are not limited to, studies concerning- insures uniformity of presentation yet permits (1) Construction problems. the flexibility imposed by terrain analysis. (2) Movement. b. Primary Requirement. The primary re- (3) State of ground. quirement for a terrain study at army, corps, (4) Water resources. or division level is that it must present the (5) Lines of communication. intelligence in a form that can be easily uti- (6) Site selection. lized by field units. The study must be concise, (7) Coast and landing beaches. presenting only pertinent information. Written (8) Inundation. description should be kept to a minimum. In- (9) Urban areas. telligence should be presented graphically (10) Barriers. whenever possible. (11) Defenses. c. Automation. The intelligence portion of 132 the Tactical Operations System (TOS) auto- (printed in gray monochrome) or is an overlay matic data systems within the Army in the to the map. Appropriate symbols are used to field (ADSAF-75) is an information process- present items of terrain intelligence. Con- ing system which uses automatic data process- ditions for movement are portrayed by des- ing equipment as a tool for battlefield com- ignated movement colors. manders to help them exercise command and c. Regions. Terrain features exist in certain control of their forces and make effective and patterns or combinations, which create distinc- timely decisions. The computer center accepts tive terrain regions. Usually the area of study information from various sources, including encompasses several terrain regions. The re- that from forward observers as well as from gional description section of the terrain study other computer centers. This information is gives the user an understanding of the terrain automatically assembled, sorted, evaluated, and by explaining the combined effect of the ter- stored by the computer. This computer drives rain features in the regions. This section con- an automatic, constantly up-dated map display sists of a sketch map delineating the terrain which provides the commander with a view of regions and of brief descriptions summarizing his entire operation. The map includes symbols the terrain intelligence for each region. representing the size, type, and location of all It may be printed on the back of the terrain forces, both friendly and enemy, as well as study map. The information presented in the the terrain features, supply dumps, and other regional description section enables the user intelligence information necessary for the ef- to evaluate the factors influencing movement fective evaluation and direction of the opera- and to interpret changes in movement which tion. This computer center consists of a central might be caused by changes in weather. processor, memory units, and auxiliary equipment. It also has an automatic communications 152. Reproduction switching capability which permits contact Reproduction of terrain studies should be with all units having an organic intelligence done by the fastest, cheapest, and easiest section and a primary intelligence collection method. Only as many as necessary for pri- mission. In addition, it has operating and mary users should be made. The engineer monitoring controls for the system. topographic battalion assigned to army has the 151. Compilation capabilities for map reproduction. The battalion can draft and reproduce in bulk the terrain a. Format. The format suggested for the study map mentioned in paragraph 151. It can terrain study consists of three parts: text, a also perform the other printing and drafting terrain study map, and a regional description necessary for the reproduction of terrain section. A fourth major paragraph, "Analysis studies. The engineer topographic company as- of Area of Operations," is prepared by the signed to corps has basically the same capabili- intelligence officer. The scope of this paragraph ties as the topographic battalion in the type is described in FM 30-5. The text follows the of work it can do, but is limited in volume sequence of the sample terrain study (app. C). and equipment. A division has no organic It presents the terrain intelligence called for topographic units. Terrain studies are produced in the applicable section of the form Tables by means of duplicators which can produce a and charts are used to simplify, amplify, and map-size paper. The type and quality of terrain clarify the presentation. The text should be as studies are limited only by the degree of skill concise as possible. and imagination on the part of the personnel b. Map. Wherever possible, terrain intelli- who are responsible for this function. gence should be presented on a terrain study map, based on a topographic map of appropri- 153. Dissemination ate scale. A map scale of 1:50,000 is usually The Engineer or Engineer Terrain Detach- utilized for brigades and divisions. Corps and ment, or G2 Staff Engineer Officer, dissemi- army headquarters usually do not require a nates the completed terrain study to the G2 scale larger than 1:250,000. The terrain intelli- and other interested staff elements. The G2 gence is overprinted on the topographic map utilizes the terrain study according to the tac- 133 tical situation and presents the resulting ter- in planning and preparing their own terrain rain estimate to the commander. If necessary, studies. A copy is sent to higher engineer the terrain study is disseminated to subordi- headquarters, and another is sent through nate and adjacent units. The terrain study is enginner channels to the Office of the Chief of also disseminated through engineer channels. Engineers. Copies are sent to lower echelons to assist them

Section II. TERRAIN AND CLIMATE 154. Basic Factors Affecting Terrain be furnished. Planning of airborne operations, The basic factors for a terrain analysis are amphibious operations, and other special op- discussed under item 2 of the terrain study erations requires knowledge of weather ele- (app C). The factors discussed are climate, ments not usually required in normal ground topography, and when applicable, coastal hy- operations. These considerations are discussed drography. Although climate and ocean- in greater detail in manuals pertaining to air- ographic aspects of coastal hydrography are borne and amphibious operations. not elements of terrain, they have a direct in- b. Factors. The methods of describing vari- fluence on the usefulness of an area for mili- ous factors of climate are discussed below. tary activities. Appendix C compiles the ter- (1) Visibility. Certain fixed data are best rain intelligence that is pertinent to the area presented graphically. Times of sun- of the planned operation. The extent of the rise, sunset, moonrise, moonset, area will vary with the echelon performing BMNT, EENT, and phases of the the compilation. Terrain studies at higher moon are best presented on a chart echelons may present fairly extensive descrip- to indicate periods of degree of visi- tions for planning purposes, but terrain studies bility. Such a chart is included in the at lower echelons, having a more definite di- sample terrain study. Where perti- rection and limit as to area, time, and purpose, nent, tide movements can also be pre- restrict their descriptions to the intelligence sented on this chart. Other deterring applicable to the operation planned. influences on visibility, such as fog, smoke, dust, or snowstorms, are dis- 155. Climate cussed in the text. a. Elements. The elements of the climate (2) Temperature. This information is discussed in a terrain study include visibility, generally presented in tabular form. temperature, precipitation, humidity, winds, Temperature predictions based solely clouds, and electrical disturbances. Not all on climatic studies cannot forecast must be discussed in every terrain study, be- the expected temperatures, but can cause the factors selected depend on the area, describe the range of temperatures time, and type of operation planned. The area that can be expected in a particular of operations influences the description of the location by either of two methods. By climate. The climate of a large area may be the first method, the mean tempera- described in general terms, whereas a descrip- ture, the mean maximum and mean tion of a small area will be quite specific. The minimum, and the absolute maximum importance of certain elements of climate de- and absolute minimum temperatures pends upon the area. The time that an opera- which can be expected for the period tion commences determines the type of intelli- can be indicated. The mean tempera- gence presented. Climatic data must be used ture alone has little significance since if the starting date is more than a week or it gives no indication of the range of two in the future. (Weather forecasts will be the temperature variation. The sec- used in the terrain estimate for 5 days or less.) ond method is to tabulate the number The type of operations planned determines the of days of the period that the tem- pertinent elements of climatic information to perature can be expected to exceed or 134 fall below stated temperatures. Tem- of days during a specific period that perature effects on other terrain fea- a certain degree of cloud cover can tures should be described adequately be expected. There is also a statement when significant, such as effect on soil as to what time of the day or night trafficability and freezing or thawing certain cloud coverage can be ex- of water bodies. pected. Related conditions such as (3) Precipitation. This information, storms and fog are also described based on climatic studies, can state when applicable. the type and amount of precipitation (7) Electrical disturbances. This subject encountered during a particular pe- is discussed only when it has an im- riod; the number of days within that portant effect on proposed operations. period on which certain amounts of The type of disturbance, its period precipitation can be expected; and the of occurrence and duration, and its variability of precipitation from year effect on planned operations are de- to year. A statement of the total scribed in the text when pertinent. amount of precipitation that can be expected over a period of time has 156. Natural and Manmade Features little significance in itself, since a 3- a. Relief. Relief is described in the text and inch rainfall means one thing when symbolized on the map to highlight significant spread over 30 days and a totally relief features, but not to repeat the detail of different thing when concentrated in a topographic map. The general picture of the 1 day during the 30-day period. The relief of an area may be indicated by ridge effect of precipitation on other ter- and stream lining, which accentuates the ma- rain features, particularly water jor ridges and drainage patterns. This consists bodies and the trafficability of soils, of emphasizing the streams by drawing over should be described. them with a blue pencil and emphasizing (4) Winds. Wind data based on climatic ridges with brown pencil. Ridge lining or research present the direction, inten- stream lining can be used separately, if de- sities, and duration that can be ex- sired, but the combination of the two is more pected over a period of time. These effective. Ridge and stream lining emphasizes facts are best expressed graphically the compartmentation of an area, but does not by means of a wind rose or may be show relative elevations or slope (fig. 57). referenced to the Weather Map Scale Another method is to emphasize the principal of Wind Velocity. Wind rose data may contours of an area. This is done by tracing be secured from AWS when specifi- over certain critical contour lines with a heavy cally required by a commander. The black pencil or by using different colored pen- effect of wind on surface materials cils to indicate different elevations. This and on waves is described when per- method has the advantage of not obscuring tinent. details on the map (fig. 58). Sharp slopes, such (5) Humidity. Exact descriptions of hu- as embankments, steep riverbanks, and cliffs midity are not usually necessary, but are indicated by a red movement symbol when the effects of humidity on operations traverse appears to be impracticable. In cer- is described when significant. The de- tain cases, an area may be cut by numerous scription should consider fog con- draws and gullies which are significant but ditions and the effect of humidity in are not shown on topographic maps because reducing the efficiency of personnel their depths are less than the contour interval. or in creating problems of storage These draws and gullies are symbolized on the and maintenance of supplies and map. The effect on movement is discussed equipment. under "movement" and illustrated graphically (6) Clouds. Data based on climatic re- by movement symbols. cords signify the approximate number b. Drainage and Hydrography. Since drain- 135 Figure 57. Ridge and stream lining. age features are subject to change at least studies usually include a soils map. At army seasonally, it is important that the terrain and lower headquarters, this will not usually study describe the present condition of the be feasible. A description of the types of sur- drainage features. The degree of detail in the face materials is included in the surface ma- description is usually determined by the eche- terial section of the study. The effect of surface lon at which the study is prepared and the materials on cross-country movement is an im- primary purpose of the study itself. A higher portant factor of the terrain study and is de- echelon indicates only the major features on scribed graphically in that section. Surface ma- the terrain study map, but lower echelon study terials are also discussed in the sections on covering a smaller area can indicate the minor construction sites and construction materials. drainage features and give detailed descrip- e. Manmade Features. The terrain study de- tions of them. scribes those manmade terrain features which c. Vegetation. Forests are indicated graphi- have particular significance or which require cally. The type of trees, deciduous and ever- more detailed description to be of value. The green, the density of the forest, and the range more common manmade features are discussed of trunk diameters are noted on the map. The below. text describes other significant vegetation in (1) The road-bridge-bypass system is de- the area and the effect of weather on the vege- scribed because of its influence on tation. Vegetation may be discussed under con- vehicular movement. A higher echelon cealment, fields of fire, obstacles, and any other study may describe graphically only pertinent aspects of the terrain. the primary roads whereas a division d. Surface Materials. Higher echelon terrain study usually describes the secondary

136 Figure 58. Contour emphasis.

and tertiary systems as well. Impor- are given in a table. tant bridges and bypass sites are in- (3) Principal cities and towns are indi- dicated. (See DIA, AP-1-335-3-1-65 cated on the terrain study map, and -ADMIN and DIAM 57-5 for route are listed further in a table. classification symbols.) (4) Railroads are shown on the terrain (2) Airfields of all types are described. study map, with detailed information Their locations are shown on the in a table. map by standard topographic symbols (5) Hydrologic structures of all types are and an indication is given as to their described, with detailed information size and condition. Further details in a table.

Section III. MILITARY ASPECTS 157. Operations rain for an operation requires a knowledge Determining the military aspects of the ter- of the terrain and of the operation planned. 137 Not having complete knowledge of any specific ive shells are examples of such features.) The military operation, the person preparing the possible effect of terrain on nuclear actions is terrain study should describe the military as- described when pertinent. pects in terms of generalized operations. The intelligence officer using the study will inter- 160. Cover and Concealment pret them in terms of the operation being This includes a discussion of the problem of planned. This is particularly true of key ter- constructing installations to provide cover, rain features and avenues of approach. De- such as foxholes, bunkers, and underground scriptions of the aspects of terrain vary with installations. The means available for provid- the echelon. At army level, descriptions are ing cover from nuclear action is discussed general; at division level they are more de- when applicable. Concealment is described in tailed and specific. the text with reference to pertinent terrain features such as forests which are portrayed 158. Key Terrain Features graphically. The amount of concealment and The determination of key terrain features to what extent various type units can utilize requires a knowledge of the terrain, the ob- it are discussed. jective, and the plan of operations. As a rule 161. Obstacles the person making this study may not have a complete knowledge of the plan of operations, The description of obstacles includes a de- and therefore, he must determine those fea- scription of the general hindering character- tures that have a controlling effect on the sur- istics of the terrain and a description of rounding terrain and list them as probable key specific obstacles. The explanation of the gen- terrain features for consideration by the user. eral obstructive elements of the terrain is an The description of these features includes a overall description and includes terrain fea- discussion of their significance. tures which are unimportant singly, but which constitute obstacles cumulatively, such as sys- 159. Observation and Fields of Fire tems of irrigation or drainage ditches, ter- a. Observation. The description of observa- races, and hedgerows. These are described in tion includes an evaluation of the ground and the text and indicated graphically by move- air observation in the area, and a brief dis- ment symbols. Specific obstacles, such as rivers cussion of the terrain features in that area that or escarpments, are described individually. affect observation. Periods of visibility are de- Obstacles that are known to be impracticable scribed by a visibility chart in the weather and for crossing by personnel or equipment are climate section. The effect of the terrain on outlined by red hachuring. observation by special devices such as radar, 162. Avenues of Approach infared equipment, and sound-ranging devices is described when applicable. The description The determination of avenues of approach of observation is generally included in the involves a summation of all other military as- text. A lower echelon study map may indicate pects as they affect the mission of a particular the location of individual observation points. force. Fixing the avenue of approach involves a tactical decision which is beyond the scope b. Fields of Fire. The description of fields of the engineer intelligence officer. His role in of fire in the terrain study is included in the the preparation of a terrain study is to present text, and is primarily concerned with flat- information on the available avenues of ap- trajectory fire. The description includes a proach for consideration by the G2 and the general evaluation and a discussion of the ter- commander. This information is included in rain features that affect fields of fire. Features the text. It includes a description of the which limit or restrict fields of fire are de- avenues of approach and a brief discussion of scribed in detail. Terrain features that create their advantages and disadvantages. special problems in the use of high-trajectory weapons are described when they exist. (Areas 163. Movement of marsh or volcanic ash that smother explos- The description of cross-country movement 138 conditions is the most important and detailed the availability of materials for construction of the descriptions of military aspects of the in the area. Availability of building materials terrain. The description of movement in the is discussed generally under military aspects text is devoted to a general evaluation of con- of the terrain. Detailed reports on the sources ditions for movement in the area and a dis- of construction materials are prepared separa- cussion of the terrain features and weather ately as required by engineer units. conditions which affect movement. Movement is shown graphically on the terrain study map 165. Suitability of Sites for Construction by color symbols which represent an evalua- The description of construction sites includes tion of movement conditions. The effect of all a discussion of sites for roads, airfields, and terrain features is considered in the text on other surface and underground installations. movement evaluation. The specific meaning of This description should be suited to the needs symbols as applied to the area of study is ex- of the echelon for which the study is prepared. plained in the margin of appropriate classifi- The description does not indicate specific sites, cation symbols. A more complete discussion of but describes the general suitability of the area areas of poor or doubtful movement than is for various types of construction. Building sites possible on the terrain study map is contained are discussed generally in the text. Detailed in the regional description section, to enable reports on appropriate sites for specific con- the commander to determine conditions under struction projects are prepared separately as which movement is possible through the area. required. 164. Construction Materials 166. Water Supply The description of construction materials The description of water supply enumerates presents information on the availability of con- the sources of water available in the area and struction materials in the area of operations. evaluates their suitability for use by the troops. It includes data on the presence of developed It includes a discussion of natural water and undeveloped sources of rock, sand, gravel, sources and water supply systems. When per- and aggregate, and of stocks of lumber, steel, tinent, the water requirements of the civilian and other construction materials. It is not a population are discussed. Water supply is dis- detailed report, but presents general data on cussed in the text.

Section IV. COASTAL HYDROGRAPHY

167. Describing Coastal Hydrography scription to coastal hydrography is discussed a. Presentation. Descriptions of coastal hy- below. drography are of interest primarily for am- b. Text. The text describes the features of phibious operations. They differ from overland coastal hydrography, such as sea approaches, operations only in the method of transporta- beach area, sea and surf, and tides. The de- tion and types of routes by which they arrive scription is coordinated with the graphic at the area of operations. The terrain study presentation. The effect of other terrain fea- for an amphibious operation includes: text, tures on coastal hydrographic conditions is terrain study map, and tables. These are the also described, and includes the effect of in- same elements which are in the land-operation land surface materials on beach composition. study, but the terrain study for an amphibious e. Terrain Study Map. The terrain study operation must also include a means for pre- map shows potential amphibious landing areas. senting detailed intelligence about the landing Since the terrain study map may be of too area. This is done by extending the three ele- small a scale to be of value as a description ments of presentation mentioned above to in- of the landing area, it is generally used to de- clude descriptions of the landing area, and pict the configuration of the coast line, location by use of a fourth element, the beach profile and length of the beaches, and location of exits diagram. Application of this method of de- from the beaches. 139 a i I 4

0a~

140 d. Description. A description of both the hy- map describes the general configuration of the drographic and terrain conditions for each coast, the location and length of the beaches, landing area is included in a table. and the beach exits. The regional description e. Beach Profile Diagram. The beach profile deals with the beaches as part of topographic diagram (fig. 59) is a large scale sketch of regions. The landing-area map presents a detailed graphic description of the beaches. It the offshore and nearshore area, the shore, and portrays the dimensions of the beaches and the the coastal terrain (hinterland). The water location levels at high tide and low tide are shown in of obstacles areas, and describes the beach exits. The colors used in the landing-area the offshore, nearshore, and foreshore areas. map conform to the color key used in all move- In addition, the beach widths at high water ment maps. The water tint usually extends to level and low water level and some of the the high water shoreline, or at time to mean sea coastal terrain are shown. A profile of the area level, depending upon the mapping agency. to the rear of the beach, showing landmarks One or more profiles are used to describe the visible from the sea, is included if deemed beach gradient. If necessary, the area to the necessary as a navigation aid for landing craft. rear of the beach is included to indicate the Other data may be included if it is pertinent position of landmarks as seen from seaward. to the operation. d. Sea and Swell. Sea is defined as waves caused by local winds, whereas swell refers to 168. Sea Approaches wind-generated waves that have advanced be- a. Offshore Approaches. The offshore ap- yond the region of generation. The direction proaches are usually of interest only to naval of sea is that of the local wind, whereas the forces and therefore are not described in the direction of swell is independent of, but may terrain study. When description is necessary, coincide with the local wind. Both sea and a hydrographic chart may be utilized. swell may be present at the same time. Sea b. Nearshore Approaches. The nearshore ap- and swell must be described in the text, with proaches are of primary interest to landing roses that show the frequency of various height forces and, as such, require a detailed descrip- categories by direction. tion. The description should present a general e. Breakers and Surf. Surf is the disturbed evaluation of the nearshore area, and describe water area extending from the outer breaker bottom conditions and the effect of sea, swell, line to the limit of uprush on the beach. breakers, surf, tides and currents. Also de- Breakers are waves that shoal over a reef or scribed are any special phenomena such as sea on a shore. Hazards to landing increase with vegetation thick enough to be classed as an increasing breaker height, and vary with obstacle, ice conditions, unusual or tricky cur- period of waves, type of breakers, and the rents. The landing area map presents a graphic direction of breaker approach onto the beach. description of the nearshore area. The general Breakers and surf are described by the text, relief of the area is described by contours based and breaker roses show frequency by direction on the hydrographic chart datum plane. Ob- of specified breaker height ranges. stacles are located on the map and any special f. Tides. Tide information is presented features are identified by special symbols. graphically. Curves portray times of high and Representative profiles, as necessary, describe low tides, and can be incorporated into the the gradient of the nearshore area. visibility chart. A chart showing the tides dur- c. Beaches and Beach Exits. The text pre- ing the period of the study is included in the sents a general description of the beach area, margin of the landing-area map for predicting covering such items as the capacity of the the heights of the water at any given time. beach, its composition and trafficability, and Special tidal conditions and tidal currents are the capacity of beach exits. The terrain study described in the study text.

141 CHAPTER 9

TRAFFICABILITY

169. Estimating Soils Trafficability ditions are given in figure 60. This figure is The purpose of this chapter is to assist in- explained in paragraph 178. telligence and reconnaissance personnel to 171. Topography determine the trafficability of soils to support cross-country movement of military vehicles. The effects of slopes on soil requirements Increased emphasis on the military concept of for vehicle performance can be shown in dispersion, which requires cross-country move- quantitative units when actual measurements ment has increased the requirement for infor- of the cone index (para 174d) can be made, mation on soil trafficability. Most information but in estimates of trafficability only general on trafficability pertains to military vehicles statements concerning slopes are feasible. operating on various unfrozen soils in the Slopes require better soil traction conditions temperate zones. The procedures for measure- for vehicle movement than does level terrain ment of soil trafficability can also be applied of a similar soil type. Other factors pertaining to unfrozen soils that have been subjected to to trafficability that must be kept in mind are freeze-thaw cycles. An estimate of trafficability that ridges are generally more trafficable than can be made with the aid of this chapter if the adjacent valley, that downhill travel is something is known of the general weather easier than uphill travel, and that low tire conditions, the topography and the soils of pressure increases traction. During the dry the area. season, sand slopes of approximately 30 percent are impassable. Fine-grained soils and 170. Weather and Climate sands with fines which are poorly drained may Information about the weather and climate be trafficable up to a 45 percent slope. During is available from meteorological records, and the wet season a 30 percent slope is the maxi- climatology textbooks, and by interrogation of mum that should be tried on any type soil. prisoners. Only two general conditions of weather apply to trafficability estimates, the 172. Soils Maps dry period and the wet period. Two types of soils maps exist. One type classifies the soils according to the Unified Soil a. Traficability During Dry Period. During Classification System (USCS), as used in a dry period all soils usually are passable unless determining trafficability. The second type of the area is low-lying and poorly drained or is soils map employs the agricultural system of kept wet by underground springs. Sand in a soil classification (ASSC). This type is not dry state is less trafficable than in a wetter used by the military. It is mentioned here to condition (with the exception of quicksand). avoid confusing it with the USCS. Soils are b. Trafficability During Wet Period. When formed by the action of the following factors: moisture is added to a soil its strength is parent material, climate, age, chemical action, changed. Different soils are affected different- topography, and vegetation. A trained analyst ly by moisture. During a wet period, all soils can estimate the soil types by using a geologic with the exception of clean sands and gravels map, providing he has a general knowledge of provide poor trafficability. The relative traf- the climate, the topography, and the vegeta- ficability ratings of soil types under set con- tion of the area. 142 173. Aerial Photographs it will support 40 to 50 passes of very light vehicles such as the M29 amphibious cargo The full utilization of aerial photos in esti- carrier. Heavier vehicles will break through mating trafficability is presently being studied. after 2 or 3 passes. At present the following information pertaining to trafficability is obtained from aerial d. Obstacles. A complete assessment of the photographs. trafficability of a given area must include an evaluation of obstacles such as forests, rivers, a. Topography. Aerial photographs are a boulders, ditches, hedgerows, steep slopes and good source of topographic information. Esti- cliffs, and embankments. Aerial photographs mates of elevations and slopes can be made are valuable in identifying these features. from stereopairs by properly instructed personnel. Accurate elevations and slopes can 174. Trafficability Terms be obtained by trained operators using me- a. Trafficability. The capacity of a soil to chanical equipment such as Multiplex and Kelch plotters. withstand traffic of military vehicles. b. Soils and Moisture Conditions. In the b. Bearing Capacity. The ability of a soil to support a vehicle without excessive settle- present stage of development, the techniques ment of the vehicle. California Bearing Ratio for identifying soils from airphotos are so is used in denoting design values. complex that only well-trained technicians can employ them to their fullest extent. However, c. Traction Capacity. Ability of a soil to certain general facts may be used to advantage resist the vehicle tread thrust required for by personnel with a minimum of training. For steering and propulsion. instance, orchards usually are planted in well- d. Cone Index. A numerical indication of drained, sandy soils; vertical cuts are an evi- the carrying ability (resistance to penetration dence of deep loessial (silty) soils; tile drains by wheels and tracks of vehicles) of a soil. in agricultural areas indicate the presence of An index of the shearing resistance of soil poorly drained soils, probably silts and clays. obtained with the cone penetrometer; a di- On a given photo, light color tones generally mensionless number representing resistance signify higher elevations, sandier soils, and to penetration into the soil of a 300 cone with lower moisture contents than do dark color a 1/2-sq in. base area (actually load in pounds tones. The same color tone does not always on cone base area in square inches). TM 5-530 indicate the same soil conditions even on the discusses this in detail. same photo. Color tone may have entirely dif- e. Remolding. The changing or working of ferent significance on two separate photos. a soil by traffic, or by a remolding test. Re- Also, natural tones are apt to be obscured and molding may have a beneficial, neutral, or det- modified by tones created by vegetation (na- rimental effect on soil strength. tural and cultivated), plowed fields, and shadows of clouds. f. Remolding Index. The ratio of remolded soil strength to original strength, determined c. Vegetation. Dense grass, especially if wet, in accordance with procedures described in will cause slipperiness. Tall grass will often TM 5-530. restrict visibility. Heavier vegetation such as g. Rating Cone Index. The measured cone brush and trees will decrease trafficability if index multiplied by the remolding index; it the vehicles must push aside this vegetation expresses the soil-strength rating of an area. as they advance. The presence of vegetation in sands usually stabilizes the soil, thus increas- h. CriticalLayer. The soil layer in which the ing its trafficability. Decaying vegetation in- rating cone index is considered a significant cluding the roots, found especially in the measure of trafficability, or the layer of soil northern latitudes, adds to the support of the which is regarded as being most pertinent to soil if the soil is weak. The limited testing that establishing relationship between soil strength has been done shows that if the mat of partial- and vehicle performance. Its depth varies with ly decayed vegetation is 6 or more inches thick the weight and type of vehicle and the soil

143 profile, but it is normally the layer lying 6 or 1. Mobility Indez. A dimensionless number 12 inches below the surface. which results from a consideration of certain i. Vehicle Cone Index. The index assigned vehicle characteristics. to a given vehicle that indicates the minimum m. Maximum Tractive Effort. The maxi- soil strength in terms of rating cone index mum continuous towing force or pull a vehicle required to permit 50 passes of the vehicle. can exert expressed as a ratio or percentage j. Stickiness. The ability of a soil to adhere of its own weight. to vehicles, wheels, and tracks. n. Fine-Grained Soil. A soil of which more k. Slipperiness. Low traction capacity of a than 50 percent of the grains, by weight, will soil's surface due to its lubrication by water pass a No. 200 sieve (Unified Soils Classifica- or mud. tion System (USCS)).

Vebicle Caeor Soil Rffect of Il 1 2 I i gI 5 1 6 1 7 Typo Slipr- Stick. Vehle. Cone Id Sbo Lo.e Ias. LO 60 bO IT a, 1io. L' F r I I 7 I II F I m SHgh T.eay, Wvetaeton. Condtion

None SPSM son. None GM Nome None SM Non one C1 Slight Moderate CC Slight Slight sc Sliaht Slight Slight M Slight sll~tSlight None Slight None Ica Slight None

None Nlione Severe Sc Moderate oderat SM-Sc Slight None 8 BSevre SlghModerate GM Slight SM slight CL Moderate McG.^t -L Moderate CL M oderat OL Moderate Moderate C Slihbt Pn Mdrate

GV GP one on. Severe slere GC Severe Moderate Severe Moderate

SSM Severe Severe Svere Moderste SPc Slight None M Slight Slightsilsbt COL Slight aMC, Severe Slight Severe Slight OL Sliht cR Sre Pt Severe Slight PROBaBITYS OF VIEiCL. "O" O LETVEL

xoeLlent Goreater ta g C Go r eliability, bse.d o anazlyis of dat GCd 76 to 9% = aIr reibility, bed on jieinnt ir 50gWto 5% Proor Lo.. tan 50% ot: Velhicle cater coe inx rae a.n givenr . tL U.

. Ale.. only to d ehicles without traction det.ces.

Figure 60. Soil tra.ficability classification (USCS). 144 o. Coarse-GrainedSoil. A soil of which 50 60 for those desiring this technical informa- percent or more of the grains, by weight, will tion. For most trafficability purposes this in- be retained on a No. 200 sieve. formation may be folded out of view to p. Sand with Fines, Poorly Drained. A sand simplify the reading of the remainder of the in which water content greatly influences the trafficability chart. Information on the trafficability characteristics. These soils react strength measurements is given in TM 5-530. to traffic in a manner similar to fine-grained 176. soils. They usually contain 7 percent or more Slipperiness and Stickiness of material passing the No. 200 sieve, and The information on figure 60 pertaining to little or no gravel. stickiness and slipperiness is self-explanatory. The following is general information on each 175. Soil Trafficability Table of these two factors. a. Soil Type Symbols. The soil type symbols a. Stickiness. No instrument for measuring used on figure 60 are those employed in the the effects of stickiness on the performance Unified Soil Classification System (USCS). of vehicles has been devised. Stickiness will The symbols are given on the extreme left of occur in all fine-grained soils when they are the figure and also in the graphic portion. The comparatively wet. The greater the plasticity duplication aids in the reading of the graphs. of soil, the more severe are the effects of sticki- These letter symbols are explained in table 2. ness. In general, stickiness will have adverse Hyphenated letters indicate a mixture of types effect on the speed and faclity of travel and of soils. steering of all vehicles. It will immobilize Table 2. Soils Symbols small tracked vehicles like the M29 weasel, Snmbol. but will not stop the larger and more power- GW -__--_-___ gravel-sand mixtures, little or no ful military vehicles. Removal of fenders will fines. reduce stickiness effects on some vehicles. GP ______gravel-sand mixtures, little or no b. Slipperiness. Like stickiness, the fines. effects SW __._____ gravelly. sands,. little or no fines. of slipperiness cannot be measured quantita- tively. Soils which are covered with water SP ___-g____- - gravelly sands, little or no fines. or CH ___---______inorganic clays of high plasticity, fat a layer of soft plastic soil usually are slippery clays. and often cause steering difficulty, especially GC ._.--______-gravel-sand-clay mixtures. to rubber-tired vehicles. They can often im- SC ______sand-clay mixtures. mobilize vehicles, especially when slipperiness CL _.- _____.gravelly. .. clays, sandy clays, inorganic is associated with low bearing capacity. Slip- clays of low to medium plasticity, periness effects assume greater significance on lean clays, and silty clays. slopes. Sometimes slopes whose soil strength GM __. ______gravel-sand-silt.. mixtures, is adequate may not be passable because of SM ______sand-silt mixtures. slipperiness. The use of chains on rubber-tired ML __-______--low plasticity silts. vehicles usually will be of benefit in slippery MH _....i..__-inorganic silts, micaceous or diato- conditions. maceous fine sandy or silty soils and elastic silts. 177. Vehicle Categories OL --- _. ._....organic silts and organic silty clays Military vehicles are divided into s e v e n of low plasticity. categories according to a cone i n d e x range OH ___-_-____-organic clays of medium to high plas- as shown in table 3. These vehicle categories, ticity and organic silts. 1 through 7, are shown at the top of figure Peat, muck, and swamp soils are not classified in the 60. above list because such soils are almost always im- passible except for light amphibious-type vehicles. a. Vehicle Cone Index. This index is shown directly below the vehicle category range on b. Strength Measurements. The probable figure 60. It is helpful in showing the traffica- ranges of the cone index (CI), the remolding bility of vehicles below category 1 and sub- index (RI), the rating cone index (RCI), and divides each of the seven vehicle categories, the mean rating cone index are given on figure especially category 7. 145 Table 3. Vehicle Categories (1) Vehicle cone index: 85 Vehicle (2) Topography: level high topography cone index Vehicles Category range (3) Type of soil: clayey sands (SC) 1 20-29 The M29 weasel, M76 Otter, and b. Question. Is this trip feasible from the Canadian snowmobile are the standpoint of trafficability? only known standard vehicles c. Procedure in Determining Trafficability. in this category. (1) You know that the vehicle 2 30-49 Engineer and high-speed tractors cone index with comparatively wide tracks of the truck is 85. Table 3 shows the and low contact pressures. vehicle to be in category 6. The ve- 3 50-59 The tractors with average contact hicle cone index range (80-99) to the pressures, the tanks with com- right of the category in table 3 and paratively low contact pres- the written description under sures and some trailed vehicles vehicles verify the category of your with very low contact pressures. truck. 4 60-69 Most medium tanks, tractors with (2) Locate vehicle category 6 at the top high contact pressures, and all of figure 60. wheel-drive trucks and trailed (3) Find the vehicle cone index 85. The vehicles with low contact pres- number 85 must be interpolated on sures. the vehicle cone index line in the 5 70-79 Most all-wheel-drive trucks, a space between 80 to 100. great number of trailed vehicles, and heavy tanks. (4) Find the soil type SC. This is given 6 80-99 A great number of all-wheel-drive under Soil type symbol in the left and rear-wheel-drive trucks, column of the figure, and more con- and trailed vehicles intended veniently on the graphic portion of primarily for highway use. the figure. 7 100 or greater Rear-wheel-drive vehicles and (5) From the 85 (interpolated) on the ve- others that generally are not hicle cone index, move downward on expected to operate off roads, especially in wet soils. the high topography, wet-season condition graphic rectangle to the area b. Graphic Portion of Figure 60. The legend marked SC. This area is stippled. for the shading of the three graphic portions Your legend at the bottom of figure of figure 60 is given at the bottom part of the shows that the trafficability for your figure. The white indicates excellent traffica- vehicle is good in this area. There- bility, the stippled good, the striped fair, and fore, the trip is feasible from the the black indicates poor to intrafficable soil. standpoint of trafficability. The The topography and soil conditions are shown marking around the soil type area on in the following three graphs in figure 60. the figure indicates that the traffica- (1) High topography, (higher areas of bility interpretation on the chart has the terrain) wet-season condition. good reliability, as you may note in the legend. (Good reliability, (2) Low topography, (low areas of the based on analysis of data.) terrain) wet-season condition (saturated). d. Trafficability for Same Truck and Soil (3) Low topography, high-moisture con- Type on Low Topography, Wet-Season Con- dition (wet, but below saturation dition. From the 85 (interpolated) on the ve- point). hicle cone index, move downward into the low topography, wet-season condition graphic rec- 178. Use of Figure 60 tangle to soil type SC. Note that the traffica- a. Mission. You have a rear-wheel drive bility is good, as indicated by the stippling. truck with which to deliver supplies cross Reliability of this trafficability interpretation country to another area. You have the follow- is fair, based on judgment. ing information: e. Trafficability for the Same Truck and 146 Same Soil Type on Low Topography, High Note that the trafficability is only fair. Had Moisture Condition. From the 85 (interpo- the vehicle cone index been a few points high- lated) on the vehicle cone index, move down- er, the trafficability would have been poor. ward into the low topography, high-moisture The black on this graphic chart indicates poor condition graphic rectangle to soil type SC. trafficability and is a warning to "stay off."

147 APPENDIX A REFERENCES

1. Field Manuals FM 3-10 Employment of Chemical and Biological Agents. FM 3-12 Operational Aspects of Radiological Defense. FM 5-15 Field Fortifications. FM 5-20 Camouflage, Basic Principles and Field Camouflage. FM 5-29 Passage of Mass Obstacles. FM 5-30 Engineer Intelligence. FM 5-35 Engineer's Reference and Logistical Data. FM 5-36 Route Reconnaissance and Classification. FM 17-36 Divisional Armored and Air Cavalry Units. FM 21-40 Small Unit Procedures in Chemical, Biological and Radiological (CBR) Operations. FM 30-5 Combat Intelligence, C-1. (C)FM 30-10A Special Applications of Terrain Intelligence (U). (C)FM 30-15 Intelligence Interrogations (U). FM 30-16 Technical Intelligence. FM 31-10 Barriers and Denial Operations. FM 31-25 Desert Operations. FM 31-30 Jungle Training and Operations. FM 31-560 Combat in Fortified and Built-Up Areas. FM 31-60 River-Crossing Operations. FM 31-70 Basic Cold Weather Manual. FM 31-71 Northern Operations. FM 31-72 Mountain Operations. FM 55-8 Transportation Intelligence. FM 57-10 Army Forces in Joint Airborne Operations. FM 57-35 Airmobile Operations. FM 60-30 Embarkation and Loading-Amphibious. FM 100-5 Field Service Regulation-Operations, C-1. FM 100-15 Field Service Regulations--Larger Units. FM 101-5 Staff Officers' Field Manual-Staff Organization and Procedure. FM 101-10-1 Staff Officers' Field Manual-Organization, Technical, and Logistical Data. 2. Technical Manuals TM 3-240 Field Behavior of Chemical, Biological and Radiological Agents. TM 5-248 Foreign Maps. TM 5-249 Terrain Models and Relief Map Making. TM 5-297 Well Drilling Operations. TM 5-312 Military Fixed Bridges. TM 5-330 Planning, Site Selection and Design of Roads, Airfields and Heliports in the Theater of Operations.

148 TM 5-332 Pits and Quarries. TM 5-343 Military Petroleum Pipeline Systems. TM 6-530 Materials Testing. TM 5-541 Control of Soils in Military Construction. TM 5-545 Geology. TM 5-700 Field Water Supply. TM 30-245 Photographic Interpretation Handbook. TM 30-246 Tactical Interpretation of Air Photos. 3. Army Regulations AR 117-5 Military Mapping and Geodesy. AR 320-50 Authorized Abbreviations and Brevity Codes.

149 APPENDIX B

OUTLINE FOR TERRAIN STUDIES

1. Purpose and Limiting Considerations (6) Humidity. Describe only when signi- State the purpose and limiting considera- ficant. Describe effect when combined tions under which the study is being prepared. with other weather elements, such as This statement should include the scope of oppressive heat or wind chill. the study in area, time, and subject matter, (7) Electrical disturbances. Describe only and any information on the tactical situation, when significant. mission, or method of operations that is per- c. Topography. If pertinent, describe the tinent to the study. following characteristics by written or graphic means. Recommend the use of a topographic 2. General Description of the Terrain map overprint to emphasize particular charac- a. Synopsis. State briefly the impact of the teristics. terrain on military operations. (1) Relief and drainage systems. Use b. Climatic Conditions. Describe predicted ridge and stream lining, contour em- meteorological conditions for the period, phasis, hilltopping, or relief shading based on climatic data. Present climatic data to outline the ridge and valley systems. graphically whenever possible. The require- Use numbers, words, or standard ments of the study will determine the exact symbols to indicate critical relief or information presented and the manner of drainage conditions. presentation. (2) Vegetation. Indicate location, type, (1) Temperature. Climatic data-give and size of trees, density of planting, frequency of occurrence of tempera- existence of undergrowth, and the tures during period. location, type, and density of other (2) Precipitation. Climatic data-state significant vegetation. frequency of occurrence of precipi- (3) Surface materials. Indicate the type tation by type and amount. and distribution of soils, subsoils, and (3) Winds. Climatic data-give frequency bare rock in the area. Indicate their of occurrence of winds of certain trafficability under various weather velocities and direction. Use wind conditions. rose. (4) Manmade features. Describe fully the (4) Visibility. Present graphically data significant manmade features. Include on times of sunrise, sunset, twilight, roads, railroads, bridges, tunnels, moonrise, and moonset. Describe ef- towns, important buildings, fortifi- fect of fogs, mist, haze, and other cations, or airfields when pertinent. influences on visibility. State expected (5) Special features. Describe significant visibility by distance when applicable. special features such as earthquake (5) Cloudiness. Describe when applicable zones or active volcanoes. and separate from precipitation and d. Coastal Hydrography. Describe when visibility. Climatic data-give data applicable. Use graphic means whenever pos- of frequency of occurrence and time sible. of occurrence of various cloud condi- (1) Sea approaches. Describe nature of tions. approaches, bottom conditions, ob- 150 stacles, gradients, and coastal struc- operations. Consider both natural and tures. Use landing-area map to present manmade obstacles. information graphically. (6) Movement. From an analysis of soils (2) Beaches. Describe dimensions, traffic- trafficability, natural and manmade ability, and beach exits. Use land- obstacles, and existing routes of move- area map to present information ment, determine the ability of troops graphically. and equipment to move through an (3) Tides and currents. Describe expected area. Use standard color code to de- time of occurrence and stage of tides. scribe movement conditions. Use spe- Present graphically. Describe currents cific terms of movement whenever by direction, velocity and duration. possible; i.e.-vehicular, cross-coun- (4) Sea and surf. Describe height of sea. try, and foot. Describe type of surf, width of surf (7) Key terrain features. From an analy- band, height of surf, and expected sis of the terrain and of friendly and duration. enemy methods of operations, indicate those terrain features which appear 3. Military Aspects of the Terrain to be critical, such as a dominant From an analysis of the factors of climate, height, a highway, a communication topography, and coastal hydrography, deter- center, or an airfield. mine the following military aspects and describe them by written or graphic means. Use (8) Avenues of approach. From an analy- of an overlay to the basic topographic map is sis of all terrain factors affecting recommended. capabilities to move men and materiel, determine the avenues of approach to a. Tactical Aspects of the Terrain. The fol- the objective. Consider existing routes lowing aspects are those basic to all tactical of movement, possibilities of cross- operations. country movement, and amphibious (1) Observation. Determine the effect of or airborne or airmobile operations the terrain factors on observation when applicable. from the ground, from the air, and by means of electric or sonic devices b. EngineeringAspects of the Terrain.Deter- when applicable. mination of the following military aspects is essential to planning the engineer phase of op- (2) Fields of fire. Determine the effect of the terrain factors on the ability of erations. Include these items in written or graphic form as overprints or overlays. flat- and high-trajectory weapons to deliver projectiles to a target. Con- (1) Construction sites. From an analysis sider nuclear weapons when applica- of surface material and other terrain ble. factors, determine areas suitable for (3) Concealment. Determine the capabil- construction of roads, airfields, build- ity of the terrain to provide conceal- ings, underground installations, sur- ment for men, equipment, and instal- face defensive installations, or others. lations. Consider the effect of terrain (2) Construction materials. From an on concealment by artificial means. analysis of surface materials and (4) Cover. Determine the capability of the other terrain factors, determine the terrain to provide cover for men, probable location of rock, gravel, equipment, and installations. Consider sand, or other natural construction the problem of cover from flat-trajec- material. tory, high-trajectory, and nuclear (3) Water supply. From an analysis of weapons when applicable. the drainage system and subsurface (5) Obstacles. Determine the capability formations, determine the probable of the terrain to delay the advance of location of potable water and water military forces or impede military suitable for construction use. 151 4. Maps and Charts (as appropriate) (1) Geological. (2) Soils. a. Topographic. (3) Hydrographic charts. b. Trafficability. (4) Town plans. c. Landing (where applicable). (5) Road. d. Special maps (when needed). (6) Joint operations graphic.

152 APPENDIX C SAMPLE TERRAIN STUDY

Headquarters 15th Army Western Germany January 1945 1. PURPOSE AND LIMITING CONSIDERATIONS a. Purpose. This terrain study considers the area to the south and east of COLOGNE, Germany, for February and March. General boundaries for the zone are the towns of JULICH on the ROER RIVER (3145) and ZULPICH (3418), and the RHINE RIVER north and south of COLOGNE as shown on inclosure 1 (fig. 61). Elements of Fifteenth Army, consisting of armored and infantry units, are located west of the ROER RIVER and presumably will operate in the area with the general mission of advancing northeastward to the RHINE RIVER. b. Limiting Consideration. Information presented is based on data obtained from maps, intelligence documents, climatic study, and interrogation. Ground reconnaissance has not been made, nor have the effects of bombing been considered. 2. GENERAL DESCRIPTION OF THE TERRAIN a. Synopsis. The area during this period of the year provides favorable conditions for military operations. It is highly populated mixed farm and industrial region. Construction sites and materials are available and the communication system is excellent. Movement across the RHINE RIVER is canalized at BONN and COLOGNE. Obstacles are the ROER and ERFT RIVERS and the VILLE RIDGE. Conditions influencing movement are sensitive to precipitation. b. Climate Conditions. See inclosures 2, 3, and 4 (figs. 61-64). (1) Temperatures will present problems to the effective operation of troops in the field. Inclosures 2, 3, and 4 give compiled temperature data. (2) Precipitation in some form normally occurs every second day. Wet soils are common. Snowfalls ordinarily do not exceed 9 to 11 centimeters (6 or 7 inches). Ice, if present, is thin and will not support a man. (3) Wind direction and velocity are given by the wind roses in inclosures 3 and 4. Winds from the east are usually accompanied by severe temperature drops. (4) Visibility factors are listed in inclosures 2, 3, 4 and 5. Fog occurs rarely at this time of year, despite the high relative humidity. The high frequency of moderate to fresh winds favors the formation of low clouds rather than fog. 153 c. Topography. (1) Relief is low and gently rolling with only two exceptions: the southwestern portion of the map (HOHE VENN) has steep wooded hills and highlands dissected by deep valleys; and a low hilly ridge, hereafter known as the VILLE RIDGE, exists between the ERFT RIVER and the RHINE RIVER. This area is discussed in detail on the back of the map and later in this study. (2) Drainage. Streams cross the region generally from southeast to northwest. The ROER RIVER is approximately 80 feet wide, with no fords, and can be flooded by release of water impounded in dams to the south. The ERFT RIVER, or canal, meanders through several channels in its flood plain. These channels average 6 to 9 meters (20 to 30 feet) in width and .6 to 1.5 meters (2 to 5 feet) in depth. In many places, the river channels are flanked by marshy flats which are drained through numerous deep ditches. (3) Vegetation. The area is largely devoted to agriculture and pasture but scattered forests do exist, and these are delineated on the map with notes as to density, type, and approximate boll size. Trails and unimproved roads allow restricted passage even through the dense forests. At this period of the year, the ground will be fallow or in low cover crop which will increase its trafficability. Trees are scattered throughout the numerous mine pits in the area. (4) Surface materials.The region is generally covered by a loamy soil tending toward sandy soil in the south. In the VILLE RIDGE area, the original soils have been stripped off during mining, exposing sandstone and shale. Stream valleys are composed of fine grained silts in the northern reaches and change to sandy material upstream to the south. The soil immediately west of the RHINE RIVER is composed of sandy well-drained material. Surface materials are discussed further on the back of the movement map. (5) Manmade features. The manmade features studied include roads, railways, bridges, airfields, towns, and strip mines. (a) An excellent network of roads exists. Only the primary system, that with a route classification (FM 5-36) of X is shown on the map. In addition, secondary roads of general route classification connect many of the villages. Free egress from roads for cross-country movement is possible in most places. (b) Rail communication, as shown on the map, is very good. As a a supplement to the standard-gage system, considerable narrow-gage lines exist, particularly in the VILLE RIDGE region. Marshalling yards are located at DUREN, BONN, and COLOGNE. The tunnel on the double-tracked route between DUREN and COLOGNE is a vulnerable point, but may be bypassed through alternate routes. (c) The classification of bridges along the primary-road system is 65. Important bridges are indicated on the map with the classification noted if lower than the general class. Bridges on the secondary-road system have a general classification of 55. 154 (d) This area contains a large municipal airfield capable of handling heavy-cargo aircraft. These have been marked on the map. Also shown are three landing strips which can be used by assault aircraft. Sections of primary roads and auto- bahns may be utilized for light Army aircraft strips. (e) Most urban areas are well built-up with stone and masonry buildings. Streets, except for boulevards or freeways, are narrow, and may permit only one-way traffic to trucks and tanks. All but the larger cities may be bypassed easily. 3. MILITARY ASPECTS OF THE TERRAIN a. Tactical Aspects. (1) Observation. Observation throughout the area is generally good, although there are small areas of defilade. The VILLE RIDGE affords excellent observation of the lowlands to the east and west. The HOHE VENN area provides good points for observation of the ROER RIVER valley. Small hills afford tactical observation in the plains section. Aerial observation will be excellent, except where woods obscure the ground. (2) Fields of fire. The area provides generally good fields of fire for all weapons with two exceptions. The broken terrain of the VILLE RIDGE and the HOHE VENN limits fields of fire for flat-trajectory weapons within the ridge masses themselves. However, fiat-trajectory weapons situated on these ridges can command their lowland approaches very effectively. (3) Concealment. The mixed forested areas give good concealment from both air and ground observation. The broadleaf forests are bare of leaves during February and March and offer only limited concealment. Farming practices in this part of Germany are such that little concealment is possible in the winter cover crops, but the many farm buildings and small villages afford good concealment for small units. (4) Cover. Principal cover is offered by the stone structures that make up the cities and farm communities. In the VILLE RIDGE area, some cover can be found in the mine tunnel.q (5) Obstacles. (a) The ROER RIVER under normal conditions will offer only minor problems to an assault crossing. Opening or destroying the ROER DAM will flood the ROER VALLEY. If this is done, it will take at least a week for the ROER RIVER to re- cede, and 2 to 3 weeks for soils trafficability to return to normal. (b) The ERFT VALLEY, with its drained swamps and many canals, will restrict movement to roads in most areas. The river channels themselves are not a serious obstacle to infantry; however, a long thaw, which is quite possible in March, or an unseasonal rain can make them unfordable to foot troops. There are also lignite pits west of Koln along Erft River. (c) Wooded areas may restrict vehicular movement to narrow unimproved roads but are passable for infantry under normal conditions. (d) The VILLE RIDGE forms an obstacle of major importance to vehicular and foot movement. It may be easily defended against 155 a superior force, affording the defender excellent observation and concealment in its woods and extensive mine workings. (6) Movement. This is indicated on the movement map (fig. 61). The area as a whole provides very good movement during dry weather, and fair to doubtful movement during periods of heavy precipitation. (7) Key terrain features. (a) The VILLE RIDGE dominates the lowlands to the east and west of the hill mass. Routes crossing the VILLE RIDGE are restricted to the roads because of the extensive pits, quarries, and spoil heaps left by coal-mining operations. (b) The HOHE VENN highlands southwest of DUREN overlook the adjacent ROER RIVER valley. In this region heavy forests and steep slopes restrict vehicular traffic to the roads. (8) Avenues of approach. The main highways from the ROER RIVER toward COLOGNE offer good avenues af approach from the southwest, and represent the bet routes for breaching the VILLE RIDGE. The best avenues of approach would be to the north of JULICH-COLOGNE highway where the VILLE RIDGE may be flanked and cut off. The secondary road and rail net is adequate for support of an armored attack. The VILLE RIDGE may be flanked from the south in the vicinity of BONN, but here armored operations will be somewhat restricted and canalized by dense forests, and by the constriction of the corridor between the VILLE RIDGE and the RHINE RIVER.

b. Engineering Aspects of the Terrain. (1) Construction sites. With the exception of the mining dumps, the southwestern highlands, and the river flood plains, the area is well suited for the construction of roads, airfields, cantonments, depots, and other military surface structures. The land is level and open, the communication net is excellent, and the soil has good stability and bearing capacity. The HOHE VENN highland is better suited for underground facilities than the plains area. Solid sandstone layers are useful as floors and roofs here, and ground water will not be as troublesome as in the flatlands. (2) Construction materials. (a) Natural materials. Quarries and gravel banks are available for stone and aggregate at many places. The terraces along the RHINE and ROER RIVERS are good sources of gravel and sand, while sandstone suitable for construction purposes can be quarried west of ZULPICH. Broken rock consisting of sandstone, shale, and soil is piled in the VILLE RIDGE dumps, and west of DUREN. Forests supply adequate quantities of standing timber to cover any foreseeable needs. Small local sawmills may be useful in cutting the timber for use. (b) Manufactured materials. The heavy industrial buildings in the VILLE RIDGE and COLOGNE areas are good sources of construction steel, lumber, and similar materials needed by engineers. In addition, a large network of mine railroads exists throughout the pits and may be utilized for material. 156 (3) Water supply. An adequate field water supply may be obtained from the streams and wells of the area. Civilian water supply on farms is obtained from wells, and in cities through municipal distribution plants and systems which draw water from the major rivers. Emergency water supplies may be drawn from these sources. 5 Inclosures: Inclosure 1. Movement map of Cologne area (fig. 61). Inclosure 2. Climate conditions Cologne, Germany, for February and March. Inclosure 3. Climatic data for Cologne area for February (fig. 62). Inclosure 4. Climatic data for Cologne area for March (fig. 63). Inclosure 5. Ephemeris for Cologne area for February and March (fig. 64).

Figure 61. Movement map of Cologne area.

Figure 61-Reverse. (Located in back of manual)

157 CLIMATIC DATA FOR COLOGNE AREA, GERMANY FEBRUARY PRECI PI TATION TEMPERATURE WIND ROSE TACTICAL AIR SUPPORT

- NS -S

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._.:_.... ,_... 0'4 Y I .. i t' fl- -.. nI

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Nt_'~

Figure 62. Climatic data for Cologne area for February (Inclosure 3 to app D).

CLIMATIC DATA FOR COLOGNE AREA, GERMANY MARCH PRECIPITATION TEMPERATURE WIND ROSE TACTICAL AIR SUPPORT . . - -- I - . . 1- ... -'

u:-..r_.ad...... ;0'.% -

A. . -_ -. ... ', ...1 ...... I...

-C -

~ m77m--- ~N ; M....

- " 1- - - ~''""' "'" - "."'

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Figure 68. Clinmatic data for Cologne area for March (Inclosure 4 to app D). 158 2 z z8 I - m 0 2 z Z o kr -SN NW.. I s _,,,tf o WXo UUU W . III II 1 t'l 1- IJ I,i,,,,l 111 0 II I11/II I I I1 W D~~~ §L A If lr:,r I1 qaI) q/ I9I i ll I u It --I ~Im I S II~ I I I) l I 1 ICrr

0 0: '? III I E -7 /411 I - 1 0 a, I bU z U- e I~L I I I IL- Il A1

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00 M0 LI s~~~IL I %xoxll.\bxxmx& Ill WI~ I tI'xxx~~.KXi:.] ll~: 1fi / fOF~ LLJ zC w 0 o~~~~~~~~~~~~~~~~~~~~~~~t~~~~Ixx'i z l I II1 1IIIr~

4 I IIIIII I U ~ ~4 I) I~~~~k:Llfl II

C ; ~~ :~ ~|1 I 1IUJL S I It I I I f I NI ) rl|| 1 1 R 1-IC I~1 I IIIII F-z ! | 1 I *, II2

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a a

159 Inclosure 2. Climatic Conditions, Cologne, Germany, for February and March

Feb - Mar Temperature ('F.): Mean maximum __.- _____...... 43 49 Mean minimum _ .------33 37 Absolute maximum _----._-_____-66 72 Absolute minimum .------0 13 Number of days with: Minimum-32 F .- ....._._ 10 6 Maximum-32*F ...------2 0.4 .Precipitation (CM): Mean .-.-.. _.__._ 4.09 4.39 Maximum ..-...... 11.88 10.31 Minimum .------0.4 .7 Maximum in 24 hours . ... 3.15 2.06 Mean number of days with: Snowfall 0.01CM __.- ____...... 6.4 5.9 Snow on ground .-...... 5.3 2.0 Fog ….... 1.2 ...... :1.4 Wet soil ______14.2 13.2 Clear skies ______.______3.2 3.1 Partly cloudy skies .------14.7 19.1 Cloudy skies __------10.3 8.8 Mean relative humidity (%): 0700 LST ------84 82. 1400 LST ------_-__ 74 67. 1900 LST .------82 76

160 APPENDIX D

SAMPLE CLIMATIC STUDY

General tional Intelligence Survey (NIS) sources, and This study is divided into four parts, each from weather summaries on file at the U.S. having a different operational aspect: amphibi- Weather Bureau or Congressional Libraries. In ous, airborne, airmobile, and overland in two the field, information of a climatic nature may differing climatic regions. The studies and ac- be obtained from local Air Weather Service companying data do not refer to any exact detachments or a national meteorological serv- geographic locations, but are offered only as a ice office. The climatic study is designed to guide for format and content. provide a first estimate of weather factors affecting military operations and should not be a. Information Sources. Source material for such studies is usually drawn from climatic regarded as an operational forecast which nor- summaries on file at the Climatic Center, Head- mally is supplied by other Air Weather Service quarters Air Weather Service, from the Na- detachments.

Figure 65. How to read a wind rose.

161 b. Wind Rose. The agency requesting cli- rose is shown in figure 65. The wind rose makes matic data from Air Weather Service should use of the Beaufort scale, which is a wind specify whether the wind speed data is desired scale in which the force of the wind is indi- in kilometers, miles, or knots per hour. Wind cated by numbers with corresponding descrip- speed data is shown in compact form by means tive terms. These terms are commonly used by of a wind rose. The method used to read a wind the U.S. Weather Bureau (table 1, chap. 4).

Part I Climatic Factors Affecting an Overland Operation in the Region Surrounding OBJECTIVE ONE During May

In terms of general climate, OBJECTIVE areas or close to the ground surface are fre- ONE area has a maritime-type climate, char- quently in the mid 30's during early morning acterized by cool, humid winters and mild, hours. comparatively dry summers. The month of Rainfall is light, averaging 5 to 6 centime- May represents a portion of the transition ters (2 to 21/2 inches) for the month. This period between these two characteristic sea- amount, well distributed in time (the maxi- sons. mum reported for any 24-hour period is 2.5 In the absence of meteorological information centimeters (11/2 inches)), should not create for the exact location involved, combined data problems associated with soil moisture and from adjacent areas, both north and south, would be sufficient to minimize dust conditions. were considered to be representative of the Snow accumulations on the mountains and climate of OBJECTIVE ONE area and are pre- passes east of the area melt at this time and sented as appendix material in tabular (table provide a source of fresh water for the local D-1) and graphical (fig. 66) form. streams. Flooding of these streams is unusual. Relative Humidity is high throughout the Table D-1. Overland Operation OBJECTI'VE ONE- Di- May day, averaging 80 percent to 85 percent. urnally, the variation is relatively small, 10 Temperature ('F.): percent to 20 percent. Although relative humid- Mean Maximum ___-______.______62 ities average quite high, the incidence of fog Mean ------650 and other forms of restricted visibilities is Mean minimum _-.______38 Recorded Extremes ...... 77 to 31 quite low; about 5 percent of the time the visi- Mean Number of Days with: bility is less than 4 kilometers (21/2 miles). Fog _-_-__-__-_-_-_-_-______1 Cloud cover and visibilities are well suited Thunderstorms ------0 for tactical air support.* Rain _..._------8 Winds are primarily from a westerly direction, southwest through northwest, with an Temperature during May is usually condu- average speed of 7 to 10 knots. Approximately cive to moderate to strenuous activity. Nor- 25 percent of the time the winds are less than mally, temperature averages approximately 3 knots. 50 ° F., with a moderate diurnal and monthly range. Minimum temperatures, especially dur- * Minimum ceiling and visibility requirements depend upon the type of support and the equipment involved, and upon the type of ing the first portion of the month, in valley terrain over which this support must operate.

162 CLIMATIC DATA FOR OBJECTIVE ONE MAY

PRECIPITATION TEMPERATURE (F)

APPROXIMATE NUMBER OF DAYS IN WHICH SPECIFIED AMOUNTS MAY BE EXPECTED TO OCCUR 6 8 0TRECORDED MAXIMUM 70- -MEAN MAXIMUM 60- 50_-MEAN .0 · 4 0 - MEAN MINIMUM

3 0 J-RECORDED MINIMUM INCHES

WIND ROSE

WIND SPEED SCALE PERCENTAGE FREQUENICY SCALE I I 10 O I0 30 CALM4-12, 3-24 255-38: KNOTS 20 0-3, I

Figure 66. Climatic data for OBJECTIVE ONE-May.

163 Par Climatic Factors Affecting an Amphibious Landing on OBJECTIVE TWO During May or June

Complete meteorological observations on the approximately 80° F., with a maximum daily island were made only during a brief period range of about 20 Fahrenheit degrees. during World War II. Plantation records for Humidity is constantly high and coupled longer periods of record have been used in ar- with the warm temperatures creates problems riving at precipitation estimates. Climatic data of material storage and supply, in addition to are presented as appendix material (table D-2 adding to human discomfort. Mean relative hu- and figs. 67 and 68). midity is approximately 80 percent, with only Table D-2. Amphibious Operations OBJECTIVE slight variation diurnally. TWO Island-May and June Visibility is seldom restricted by weather factors except during brief periods of heavy Temperature ('F.): May June Mean Maximum ...... 88 90 shower activity; however, dense vegetation Mean -_------81 82 limits ground visibility severely unless some Mean Minimum ...... 75 76 form of clearing has taken place. Recorded Extremes ------93 to 73 95 to 74 Precipitationis of the brief, heavy shower- Mean Number of Days with: Thunderstorms ...... 8 type that usually occurs during the afternoon Precipitation ___------17 on an average of 1 out of 2 days. Thunder- 1.3 centimeters- storms are quite frequent, with an average of 0.5 inch ...... 12 8 storms per month. Although total precipita- 4.8 centimeters tion is highly variable from year to year, it is 0.6 to 1.9 inches ____ 4 5 centimeters- more than adequate to keep soils moist, support 2.0 inches ._------1 heavy vegetation, and present vehicular transport problems. Maximum precipitation in 24 Climatically, OBJECTIVE TWO Island has hours reported for the island during this period all the typical tropical characteristics with was 18 centimeters (7.2 inches) during May. heavy, shower-type rainfall and a small diurnal Winds are light and variable, except during and seasonal temperature range. Since the heavy showers; however, during June the island is affected by the monsoon wind, the southeast monsoon is being established and May-June period is one of transition, during southeast winds become more predominant. In which winds are normally light and variable. the forested areas, winds are usually very Temperature conditions are not conducive to light or calm, but along coastal strips they human activity, and the daily range of tem- average about 5 knots. Typhoon winds are not peratures is insufficient to alleviate this human considered a threat to operations this early in discomfort at night. The mean temperature is the season.

164 CLIMATIC DATA FOR OBJECTIVE TWO ) MAY

PRECIPITATION TEMPERATURE (E)

APPROXIMATE NUMBER OF DAYS IN WHICH SPECIFIED AMOUNTS MAY BE EXPECTED TO OCCUR 12 //// I 100O

- RECORDEP MAXIMUM 90- ¢6 -MEAN MAXIMUM

80oMEAN

-MEAN MINIMUM -RECORDED MINIMUM 70- INCHES

WIND ROSE

WIND SPEED SCALE PERCENTAGE FREQUENCY SCALE ""100T 10 20I 30 CALM 4-12 :13-24125-381 KNOTS I0 0 10 20 30 0-3 , Figure 67. Climatic data for OBJECTIVE TWO-May.

Part III Climatic Factors Affecting an Airborne-Airmobile Operation in the Vicinity of OBJECTIVE THREE During September

For the purposes of this report, it was as- equal to or greater than 4 kilometers (21/2 sumed that paratroop operations would be car- miles), and wind speed less than 13 knots. On ried out only with a ceiling value equal to or this basis, favorable weather occurs most fre- greater than 305 meters (1,000 feet), visibility quently during the midafternoon. Unfavorable

165 CLIMATIC DATA FOR OBJECTIVE TWO JUNE

PRECIPITATION TEMPERATURE (F)

APPROXIMATE NUMBER OF DAYS IN WHICH SPECIFIED AMOUNTS MAY BE EXPECTED TO OCCUR 12 100- -RECORDED MAXIMUM

4 90- -+MEANMAXIMUM

- MEAN 80- -MEAN MINIMUM -RECORDED MINIMUM 70- INCHES

WIND ROSE

WIND SPEED SCALE 0/. _ PERCENTAGE FREQUENCY SCALE Mm...... I I I I I CALM: 4-12 :13-241253KNOTS 10 0 10 20 30 0-3 1 I Figure 68. Climatic data for OBJECTIVE TWO--June.

conditions increase gradually until early morn- and equipment utilized, should be able to op- ing hours when adverse weather occurs ap- erate 70 percent to 80 percent of the daylight proximately 25 percent of the time. Tactical hours (table D-3 and fig. 69) . air support, depending upon the type needed

166 Table D-3. Airborne Operation OBJECTIVE THREE- ture is large, but normal temperatures are September quite moderate with mean maximum of 67° F. ° Temperature (°F.): September and a mean minimum of 50 F. Mean Maximum .-...... 67 Precipitation, in the form of drizzle, light Mean ______..-. . ...58 rain, or showers, occurs on the average of 2 Mean Minimum . __.__.-...... 50 Recorded Extremes ...... 87 to 38 days out of 3, giving an average September Mean Number of Days with: rainfall amount of approximately 6.35 centime- Thunderstorms -___ __..--_.______- 3 ters (21/2 inches). Heavy rainfall is infrequent, Precipitation ------_-___ 19 but when it occurs, poorly drained areas be- 2.54 millimeters (0.1 inch) ..... 9 come flooded and trafficability problems are 2.54 to 12.70 millimeters intensified. (0.1 to 0.5 inch) .------6 12.70 millimeters (0.5 inch) ___-___ 4 Fog restricts visibility to less than 800 Precentage Frequency, by Hour, of Weather meters (one-half mile) on 1 day of 10, most Favorable for Paradrop Operations often during the early morning hours. During (Ceiling 305 meters (1,000 ft.)), Visi- the afternoon and early evening the possibility bility 4 kilometers (241 miles, Wind 13 of restricted vision caused by air pollutant is ft.) even less. 0800 LST 74% 1400 LST 96% Winds are most frequently from the north- 1900 LST 91% west (see wind rose), with about 10 percent of the observations showing wind speeds Temperatures are not extreme during this greater than 13 knots. Diurnal variations in period and should not present problems of hu- wind strength or direction appear negligible in man comfort. The extreme range of tempera- this particular area.

Part IV Climatic Factors Affecting an Overland Operation in the Vicinity of OBJECTIVE FOUR During February

Climatically, the objective area has a marine result of the moderating effect of the water on climate, which implies mild, cloudy, and humid the migratory air masses. However, alternate weather (table D-4 and fig. 70). freezing and thawing of the normally water- Table D-4. Overland Operation OBJECTIVE FOUR soaked soil surface is common, creating prob- -February lems of vehicular movement due to rapid deterioration of natural surfaces. Temperature (°F.): February Precipitation Mean Maximum ______. 45 in the form of rain, drizzle, Mean ------38 and/or snow occurs on approximately one-half Mean Minimum ______.___ 32 of the days during the month. Snowfall is Recorded Extremes ____------64 to 10 usually small in amount, but is apt to be wet, Mean Number of Days with: heavy, and clinging; possibly resulting in de- Precipitation -. ------struction of overhead wires and some vegeta- 2.54 millimeters (0.1 inch) 2.54 to 12.70 millimeters tion. Snow cover is usually shortlived, being (0.1 to 0.5 inch) --______destroyed by the frequent warmer rains. Soils 12.70 millimeters (0.5 inch) ___.__ are usually water soaked; only during excep- Snowfall ...... tionally cold winters does the ground freeze to Snow on ground _-_.______any depth. Mean Relative Humidity (%) Fog occurs on 4 0700 LST 85 to 5 days during the month 1400 LST 71 and is usually quite dense, persistent, and 1900 L ST ------80 widespread, restricting visibility to several hundred meters and precluding any tactical air Temperatures usually are not severe, as a support. Cloud cover is usually present, but

167 CLIMATIC DATA FOR OBJECTIVE THREE SEPTEMBER

PRECIPITATION TEMPERATURE (F)

APPROXIMATE NUMBER OF DAYS IN WHICH SPECIFIED AMOUNTS MAY BE EXPECTED TO OCCUR 9 . 9 0 TRECORDED MAXIMUM w 80- ci 7 0 -MEAN- MAXIMUM dC 6 0 - -MEAN

50- -MEAN MINIMUM

4 0 -RECORDED MINIMUM 30-

WIND SPEED SCALE PERCENTAGE FREQUENCY SCALE I"'l""l i I CALMI 4-12 13 - 2425- 3 KNOTS 10 0 10 20 30 0-3 1 1

Figure 69. Climatic data Objective ThreeSeptember.

168 CLIMATIC DATA FOR OBJECTIVE FOUR FEBRUARY

PRECIPITATION TEMPERATURE (OF)

APPROXIMATE NUMBER OF DAYS IN WHICH SPECIFIED AMOUNTS MAY BE EXPECTED TO OCCUR 9 .I I 70 RECORDED MAXI IMUM 60 U, C3 50 MEAN MAXIMUM o; 40 MEAN 30 MEAN MINIMUM

I0 'RECORDED MINIM IUM INCHES

WIND ROSE

WIND SPEED SCALE PERCENTAGE FREQUENCY SCALE 1I""1"I' 1 1 CALM' 4-12 :13-24125-38,KNOTS 10 0 10 20 30 0-3, , , i

Figure 70. Climatic data for OBJECTIVE FOUR-February. normally the effective ceiling is about 610 ern direction, light to moderate in force with meters (2,000 feet). infrequent gale-force winds associated with Winds are predominately from a northwest- strong frontal passages.

169 APPENDIX E

NATURAL TERRAIN FEATURES

The natural terrain features shown in A, B, and C, figure 71 will serve as a guide to producers and users of terrain studies. A few of the terrain features identified on the figure may be known in some regions under different names because of local usage.

170 APPENDIX F

DEPARTMENT OF DEFENSE INTELLIGENCE INFORMATION REPORT FORMS 1396 AND 1396C

Department of Defense intelligence information will be reported on DD Form 1396 and DD Form 1396c. These forms are available through regular supply channels.

171

INDEX

Paragraph Page Paragraph Page Aerial photographs . ..-...... 173 143 Dry ____…______….42 ___.. 31 Aerosols ...... 36f 26 Humid .------44b 33 Agencies, intelligence .------23 11 Marine west coast ___…___. .. 43d 32 Air support _-_-___.---_------.60g 62 Mediterranean …--.---..... 43b 31 Air temperature .------25 13 Mesothermal ...... 43 31 Air Weather Service --- ___.- __--30a, 34e 21, 24 Microthermal __.__-___ .. _44. 32 Airborne operations ...... 141 127 Middle latitude ---- ___------42d 31 Airfields ...... 113, 114 105 Polar ...... 465 33 Airmobile operations …-_____-____141 127 Savanna ______--___-_------41b 30 All weather route ___ . _--95b...... 94 Subarctic _-...... 44e 33 Alluvial plains -___ ...... 55 52 Subtropical ____.-..______43c 32 Altocumulus clouds _----_---_--- 2 9g(2) 19 Tropical ...... 41 30 Altostratus clouds .--- .....--.- 29g(1) 19 Climate and terrain ...... 40b 29 Amphibious operations ___-__.. _ 140 126 Climatic study: Anaglyph ----.. ------18d( d(2) 10 Preparing -______.47 35 Antarctica ------_--- 54c(2) 52 Sample ___---______-___. App D 161 Arctic regions ______._____: O0 40 Cloud cover symbols .------29 16 Assault landing ______-______70f 75 Cloudiness...... - 38 26 Atmospheric pressure ------26 14 Clouds .... ______.____-___29, 38, 16, 26, Atolls _____---__- -__ -___.____._-73d 77 165b(6) 135 Avenues of approach _------49g, S0g, 40, 42 Coastal plains _-______..___53d, ... 55e(1), 48, 57, 60e, 90e, 62, 91, 140d 126 95c(l), 94, 122, Coastal ridge ...... 140e 126 137, 162 138 Coast lines ____…______.._.._-74a 78 Barrier reefs --. ______------73c 77 Collection agencies, intelligence -- 23 11 Barriers __ ….____-______136c 122 Collection effort, intelligence __. .13 7 Beach profile __-______....___.167e 141 Communication, lines _____- .____20c, 49h, 11, 40, Beaches ______..______70, 71, 73, 75, 60f, 94, 62, 93, 168c 141 123e 113 Bearing capacity of soils .- ...... 174b 143 Communication maps _____.-. __17a(3) 8 Biological agents .------48d(6), 49i 38, 40 Compartments ...... 138 123 Boulders __-____.______55b (4) 55 Cone index, vehicle ...... 174 143 Bridges -.. ______97 96 Construction: Broadleaf forest ___._____.___84c 85 Effects of vegetation .-.... 90f 91 Buildings ...... _...... 122, 125b 112, 116 In hills and mountains __60i 63 Materials-164, 1665 139 Catchment basin -- _._._...... 62b 60 Problems . ...-...... 55, 122c 52, 112 Chain, mountain __-_-_-_---_____57d Continental climate .-...... 44b 33 Chemical agents -- ____-..-- . _._.. 48d(6), 49i 38,40 Contour emphasis __-. .__.____.156 135 ___-__8c Chief of engineers ____- 16 Coral reefs ----... ___.______73 77 Chinook wind -_ ...... 27d Cordillera ___…___------_ ...... 57e 60 Cirrocumulus clouds ...... 29f(3) 19 19 Corridors ...... 139 123 Cirrostratus clouds ._...... 29f(2) 37, 40, Cirrus clouds ___ ….._____._____-_29f(1) 17 Cover and concealment .-- - 48d(3), 42, 62, City areas .-...... 122d 112 49f, 50e, 90, 113, Civilian oil pipelines ...... 6dd.10 101 60c, 90c, 138 Clay .------76e 81 123c, 121, Climate, effects of ------__-- - 54b, 155, 52, 134, 135, 160 170 142 Crops, field ...... 89a, 89 Climate, examples: Cross-country movement .--.--- 163 138 Continental ...... 44b 33 Cycle, intelligence _….------12 7 Desert .------42b 31 Cyclones, tropical ...... 32c 22

173 Paragraph Page Paragraph Page Dams ...... 119b ...... 109 Hydraulic structures ...... _ 119 109 Deciduous trees ______.____.83c 84 Hydrography .- 1----__------__156b135 Defense Intelligence Agency -__--8a 5 Hydrologic circle _...... _.67a 69 Delta plains … -______-53e 48 Ice front …__...... 66c 68 Desert climates __ 42b 31 Ice cap ______-__-_____- ___46- 34 Desert drainage ______-___-___63g 66 Index, cone vehicle _ ...... 174 143 Deserts ------_48 35 Information requirements, Determining trafficability __…-__..178c 146 terrain: Dew point ______.--- -- _____---28c 16 Airborne ...... …..141b 127 Dispatch route ______.… .______95c(5) 94 Airfields ...... 115 106 Dissemination of intelligence __..__16 8 Airmobile ...... - 141b 127 Distribution of rainfall __….______39 26 Bridges ...... 98 96 Divides, mountain _ .- . _..58c...... 61 Buildings ______126…_. 116 Documents, enemy ______-_____..21 11 Drainage ------69 72 Drainage ______...... ______62, 156b 64, 135 Hills and mountains .-._. 61 63 Drift plains ______-53h(2) 49 Hydraulic structures ...... 121 111 Drop areas ___…______.______141c 127 Inland waterways .------103 99 Drumlins ------_- 5____.53h(2) 49 Landing areas .-...... 75 80 Dry climates ______42 31 M ines ------_ 110 104 Dunes _.-.....______.___..71b, 140f 75, 126 Non-urban areas -____. ....131 118 Engineer: Petroleum and gas __._____ 108 102 Intelligence functions -_.....11 6 Plains and plateaus .----___ 56 60 Intelligence Studies ______20b 11 Quarries and pits ___.-. .___112 105 Terrain Detachment ______153 133 Railways -...... - 101 98 Ephemeral streams .------63c 66 Roads .------__96 95 Estimate, terrain _-______4 4 Rock ...... 81 84 Evaluation of railways .-__._. ... 100 97 Soils _._.___...... ___79 83 Evergreen trees ______…_____.83c 84 Urban areas .___._._____ 124 114 Example of climatic study ____- App D 161 Utilities ______.. ______128 117 Example of terrain study ______App C 153 Vegetation …_____.______91 91 Extreme climates __- _-_. ______41, 42b, 30, 31, Water supply _ .- . ___ .....147 130 45 33 Water terminals .------____ 118 107 Inland waterways -_____ ._____102 98 Fair weather route .------__--- 95b(3) 94 Intelligence: Fields of fire .-...... ____. .48d(2), 37, 39, Collection ------13 7 49e(1), 42, 61, Cycle _. ___. ______. ... 12-16 7, 8 50d(2), 90, 120, Dissemination _.-...... __ 7a, 16 5, 8 60b(2), 138 Officer __…______10 6 90b(2), 134, Processing ...... 15 7 159b Reports ---.------___ 20 11 Flood control …______-______-119a 109 Strategic .------__ 6b 4 Flood plains ______.______53f 48 Weather _ ___--- _-__---___-- 34 23 Foehn effect …2______-... 27d 16 Intermittent streams …____ ...... 63b 64 Fog ______31 22 Interrogation of prisoners .------22 11 Foothills __…_-____…_… ______….58d. .. 61 Forecasts, weather ______33 22 Jungles __------49 38 Forests _____.-...... _____.84, 85, 85, 86, Karst plains ..- ….______53k, 55c(7) 50, 60 86 87 Key terrain …._._.__…___.__-____48d, 49d, 37, 39, Glaciers _- -______-______66 67 60a, 90a, 61, 89, Glacial plains ______-_--______.53h, 49, 58 133, 158 120, 138 55e(4) Lacustrine plains __ .…_…. ___.53i, 55e(5) 50, 60 Glory-hole mining ...... 109d 103 Lakes ___-...... _____..______64, 68d, 66, 71, Grasses ______.----- 88 88 144d 129 Gravel __-----______76b 81 Landforms … ...... 51b, 53 44, 45 Gravity springs ______-_-______67c(1) 70 Lateral route __--______...... 95c(2) 94 Greenland, marginal features ____54c(1) 52 Lines of communication _ ….....20c,49h, 11, 40, Ground water ______67, 145 69, 129 60f, 94, 62, 93, High-latitude forests ______.- . .86 .. 87 123e 113 Hills -5.. ______.__. ... 59, 145d 61, 130 Locks … ...... 119d 110 Humidity ______28, 37, 44b 16, 26, Loess plains ___... ._____._____53i, 55e(6) 50, 60 155b(5) 33, 135 Low-latitude forests … ...... 84 85

174 Paragraph Page Paragraph Page Mangrove swamp ...... -.. 84b 85 Observation and fields of fire --- 48d(2), 37, 39, Manmade terrain features --..... 92 93 49e(1), 41, 57, Maps ...... 17, 172 8, 142 50d(1),55c 61,90 Marine west coast climate ...... 43d 32 60b, 90b, 113, 120, Marshes and swamps ------65, 68e 66, 72 1236, 134, 138 Maximum tractive effort ------174m 144 159a Meandering river ...... 531 48 Obstacles ...... 48d(4), 50f 37, 42, Mediterranean climate ------43b 31 60d, 90d, 62, 90, Mediterranean scrub ------85b 86 136, 161, 121, 138, Melt water ...... 66f 68 173d 143 Mesothermal climate … ...43 31 Oil, military importance ...... 107 101 Microthermal climate … ...44 32 Oil distribution ...... 106 100 Middle-latitude climate ...... 42d 31 Oil fields ...... - 105 100 Middle-latitude forests ...... 85 86 Oil pipelines ...... 106b 100 Oil tanks ...... 106e 101 Military aspects: Open-pit mines 109¢ ...... 103 Bridges ...... 98 96 Orchards ...... 89b 89 Buildings ...... 126 116 Coastlines ...... 74a 78 Passes, mountain ...... 58e 61 Drainage - ...... 69 72 Peaks ...... 57b 60 Hills and mountains ------60, 61 61, 63 Perennial stream - ...... 63aa .. 64 Hydraulic structures ...... 120, 121 111 Petroleum and natural gas ..... 104 100 Hydrology - ...... 68 71 Photographs -...... 18 ...... 9 Inland waterways - ...... 103 99 Pictomaps ...... 17a(5) 9 Jungles ------49 38 Piedmont plains ----- ...... 53g 49 Landing areas ------75 80 Pipelines, military oil ...... 106 100 Mines ...... l...... 109e 103 Pits ------. 111b 104 Nonurban areas ...... 130, 131 lrT Placer mines ...... 109b 103 Petroleum and gas ------108 102 Plains ------53, 55, 45, 52, Plains and plateaus --...... 55, 56 52, 60 145b 129 Quarries and pits ------112 105 Planning ...... 132 120 Railways --...... 101 98 Plants ------82 84 Reefs ...... 74b 79 Plateaus …...... 54,55 50,52 Roads ...... 96 95 Polar climate …----…------45 33 Rock ...... 81 84 Polders ...... 119e 110 Soils -...... 78a, 79 82, 85 Ports ...... 116 107 Terrain ...... 52, 132 45, 120 Prairie...... - 88c 89 Tunnels ...... - 80c 83 Precipitation ...... 30, 21, Urban areas ...... 123, 124 113, 114 1556(3) 135 Utilities ...... 128 117 Pressure, atmospheric ...... 26 14 Vegetation - ...... 90, 91 89, 91 Production of terrain intelligence _12 7 130 Water supply ...... 147 Quarriesl ------illa 104 Water terminals ...... 117, 118 107 Military pipelines ...... 106c 101 Railways ...... 99, 100 96, 97 Military use of railroads ------99f 97 Rain, tropical ...... 84a 85 Mines ...... 109 102 Rain forest ...... 441a 30 Rainfall ...... 30, 39a 21, 26 143 Mobility index ...... 1741 Ranges, mountain ------57c 60 Models, terrain ...... 17 8 Rating cone index ...... 174g 143 Monsoon ...... 27f 16 Reconnaissance reports ------20f 11 Moss …...... 84c 85 Reefs ...... 73, 74 ...... 77, 78 Mountains -_-_-...... 5-- - -- 7, 58, 60, 61, Relief ...... 51c, 156a 44, 135 140g 126 Remolding index - ...... 174f 143 Remote-sensor imagery - ...... 18 9 National Intelligence Survey ___20a 11 Reports, intelligence ...... 20 11 Natural gas -...... 104 100 Reserved route ...... 95c(3) 94 Needleleaf forest ...... 85d 87 Reservoirs ...... 119¢ 109 Rice fields ...... 89c 89 Nimbostratus clouds ...... 29h (2) 19 Ridge and stream lining ...... 156 135 Nipa palms -...... 84b 85 Ridge approach ...... 1396 126 Nonurban areas ...... 129 117 Rivers … ...------63, 68 64, 71 Nuclear weapons ...... 37c, 78h 26, 83 Rock ------...... 80 83

175 Paragraph Page paragraph Page Routes and roads ______95 93 Thunderstorms .------3 2a 22 Tides _____-______141 Sample __168f terrain study ___ ---_App. C 153 Topography _ ...... 51, 72, 122b Sand _-______76c 44, 75, 112, 127, Sand dunes ______48b 81 141c(4), 36 171, 173a 142, 143 Savanna -.------88b Savanna climate .------41b 3030 Tornadoes ...... …_--.. _.32b 22 Screening smokes ------48d(7) 38 Traction capacity of soils ...... 174d 143 Scrub, Mediterranean ------85b 86 Trafficability ...... 169 142 Sea approaches --- ___------168 141 Trees _…______._.______-___83 84 30 Seeps and springs - …------___ 67c, 144b 7; 0,129 Tropical climate _..______41 Shrubs _…____-______87 88 Tropical cyclones ...--.______32c 22 Silt ______76d Tropical grasslands ______.___._88b 89 Slipperiness …...... ______174k, Tropical rainy climates ______41 30 176b 14,5 Tropical regions _- -.... _____ 49 38 Soils ______76, 78, 80, 82, Tropical swamp ...... 84b 85 34 169, 1736, Tundra --. ....______.__ 46 -1o Tunnels ...... - _._.._._ 80c 83 174, 175 143, 140 Soil maps ._____.______-___-17a(1),77, 8, 81, Underground installations _.____80b… 83 172 142 Underwater topography ______72 75 Soil trafficability table ____…___175 145 Urban areas .------_-- 122 112 Soil-type symbols (table 2) .__-175a 145 Utilities ______127 117 Special operations ______140 126 Springs, artesian ____ .____-___'.7c(2) 70 Valley approach -._------139a 123 Springs, gravity _-______67c(1) 70 Valley wind .------27c 16 Springs and seeps ______-__67c, 144b 70, 129 Valleys, kinds __…_.______58b 61 Steppes ______…__42c88d 31, 89 Vectographs ..18d(2)...... 10 Stereopairs …_.___…______._.18d(2) 10 Vegetation ...... 82, 89, 84, 89, Stickiness, soil …______…_____174j, 176a 144, 145 156c 173 136, 143 Storms ______-______.___ 32 22 Vehicle categories (table 3) ……______146 Stratocumulus clouds _____…_…___29h(3) 19 Vehicle cone index ______174i, 177a 144, 145 Stratus clouds -- ______-____.___29h(1) 19 Velocity, wind (table 1) __. _.____._._____. .. 15 Streams __- _6______8______63, 144c 64, 129 Visibility ______155b(1) 134 Studies: Volcanic lava _-______53d 48 Climatic .___App.______D 161 Terrain ______-___.___App C 153 Water, sources and supply ______142, 143, 127, 128, Subarctic regions ______..___44e, 50 33, 40 146, 166 1130, 139 Subtropical climate ___ .____..___43c 32 Water table _____-______67b 69 Supervised route . ___..5c(4)...... 94 Water terminals ...- …-_…______116 107 Surf ______…______.___168e 141 Waterways, inland .- ..._...102 98 Swamp, tropical .-.__..____ 84b 85 Weather …...... -24,170 13, 142 Swamps and marshes -- ___65, 68e 66, 72 Weather forecasts ______33,.-- 34f 22, 24 Weather intelligence …______… 34 23 Temperature __ …______.___835, 1556(2) 24, 134 Weather requests ___…______. 34d 24 Terrain …______.___4, 6, 52, 4, 45, Wells …______145e 130 114, 132, 105, 120, Wind velocity (table 1) ______. - 15 136d 122 Winds ______-______. 27, 36, 14, 25 Terrain models ____ …_._.______17 8 155b(4) 135 Terrain studies ______148, 132, World rainfall ______30 21 App. C 153 World temperature ______40 28

176 By Order of the Secretary of the Army:

HAROLD K. JOHNSON, General, United States Army, Official: Chief of Staff. KENNETH G. WICKHAM, Major General, United States Army, The Adjutant General.

Distribution: To be distributed in accordance with DA Form 12-11 requirements for terrain intelligence.

* U.S. GOVERNMENT PRINTING OFFICE: 1967-0 273-544 MOVEMENT MAP COLOGNE AREA 6020'15' 51°6'55' - 7-10`45' 51o6'55' Sample Movement Color Key2A

Specific Movement Key

Mountains and steep hills generally wooded Travel restricted to the few e xistingroad--s .... 1 Gently sloping and level land:; slopes less tran 10/,sairdy or grave-1y soil;gOd move meit in all but worther -eat ..... 1A Gently sloping and level land: slopes less than l0 loamy or clayey soil; good move

Gently Moping and evel Jand, urban area Trafficwtreet retrite.d . to __2C Wooded areas Densi ty, type and thickness of trees giavn ocmap and these factors determine practicability of passage. . . .. Drained swamps and flood plains: many canals and ditches Dlsruption of canal drainage causes flooding Generally untraf fic.bl------I-4A Mine pits and spoil heaps Untraficable because of steep slopes and holes.E.. Swamps Impracticable ...... 5

LEGEND

Woods... ; - -

Raliway. multiple track (with tunneI) __ ...... - ~ -I--. =

Railway, single track

Landing strip, light aircraft ... /

Highway. autobahn, route class 40 ft X 65 T

Highway. primary, route class 20 ft. X 55 T . ...

Highway, state, route class 20 ft X 55 T ......

Bridge, railroadT. ..- or .highway -

Stream canal,. and river...... Airfield, arge municipal -0----- Escarpment and mining pits

. 9.

2 mils ' . or - 50039,30o = 6'20'15' JJ 50*39'30'

This sample movement map is not to scale 7'10'45 ' Aemen o sea S lne to,n 19_I_ ANNUALMAGNETIC CHANGE'* ' enr W)

Scale I 100O000 O I _ 22s 3 5 g M 0ooo 0 000 2000 3000 40o0 50o0 6000 70o0 0OOOMlars loon O I00 2000 3000 4O0 5000 6000oo 7000 OOO0yMrd

Contour Interval 50 Feet Prepared by The Engineer SChool, For Belvoir. 1959 Map keyed to Germany 1: 00,000 AMS, SI and RI, 1952. to which reference is made for marginal infor mation Comments concerning field usability are requested by The Department of Training Publications. The Engineer School, Fort Belvoir, irginia Fo illus trative purposes, bidge dolssfication infoematlon has been purposely omitted from this map. Route csasifi - cation infogmation has been added to the legendunder dsFi e . Movement ap of Coloe a Figure 61. Movement Map of Cologne area. RHINE PLAIN

The RHINE PLAIN consists of three related areas; (1) flood plains of the lower ROER, ERFT, and RHINE RIVERS; (2) the terraces along these rivers; (3) the prairie lands between the rivers.

Flood Plains

The flood plains of the ROER and ERFT RIVERS are quite flat and are dissected by many ditches and drainage channels. They have complex soils of silts and very fine sands; a high water table makes them difficult to traverse during wet periods. Portions of the flood plains are drained swamps with considerable organic material in the soil. Traffic is restricted to the road system by these factors, but foot troops will encounter only minor difficulty. The flood plain of the RHINE RIVER is quite narrow, as the river terraces closely approach the river on the west bank between BONN and COLOGNE. The RHINE RIVER here is 900-1400 feet wide, has a 2-4 ft/sec. velocity and is 20-40 feet in depth.

River Terraces

River terraces are poorly developed along the ROER and ERFT RIVERS, but reach a grand scale along the RHINE RIVER where four or five terraces can be HOHE VENN HIGHLAND found. They are composed of sandy or occasionally loamy soil, and are up to four miles wide along the west bank. Cross-country movement is good to excel- The HOHE VENN HIGHLAND shown on the map is the northern tip of a much lent in most weather. Slopes between terraces are usually less than 10 percent, larger forested plateau to the southwest. It has two principal landforms . . . a while the terraces themselves are practically level. One boggy spot (5) is shown dissected upland and the upper ROER RIVER valley system. between COLOGNE and BONN, but others, all of very small size, may be present on the southwestern outskirts of COLOGNE. Terrace slopes along the BOER and RHINE RIVERS are good sources for gravel aggregate. Upland

Prairie Lands This upland is made up of flattened sandstone hills 300-500 feet high with steep wooded slopes usually above 25 percent. Bluffs are common. Some of the flattened hilltops are open and are used for farming and pasturage. Principal soil These are extensive areas of very gently rolling topography mostly taken up with type is loam. Cross-country movement is good in the open areas, but steep sand- farmland. The land between the ROER and ERFT RIVERS, and that north of the stone-shouldered ravines are frequent barriers. Trails and roads provide occasional JULICH-COLOGNE highway are examples of prairie lands. Soils are sand loam to clay loam, rather thick, and are the weathered product of loess deposits. Sandy passage from the open hilltops through defiles to the lowland valleys. In this area, sandstone may be quarried. Towns are small and scattered, and construction areas are found, and are due partly to glacial outwash, and partly to the lith- sites for facilities are limited. Road and rail communication is poor as compared ology of the underlying rock. Cross-country movement over prairie land is good to the lowland plains. in fair weather, but hampered by mud to a degree dependent upon the sand content of the soil. Scattered wooded areas which usually possess soils of the same loamy nature are delineated on the map. Prairie lands are well suited for most Upper ROER RIVER Valley types of military surface construction.

This valley system is rather narrow with steep wooded sides and occasional GENERAL WEATHER-MOVEMENT RELATIONS escarpments. The valley floor does not exceed one-half mile in width but is made up of sandy gravel; cross-country movement is good under most conditions. Although February and March are months low in total precipitation, weather con- The ROER RIVER is approximately 80 feet wide in this vicinity, with a stream ditions cause soil to retain a high moisture content. Alternate freezing at night velocity of 4-8 ft/sec. Two large dams several miles upstream control its flow and thawing during the day prevents normal drainage. Freezing is seldom intense and much of the valley floor may be flooded by release of the impounded water. enough or of such a duration to facilitate movement. The snow cover normally Traffic into and out of the valley is restricted to roads, but a railroad follows does not exceed six or seven inches at any one time, which will not hinder tracked the river route into the city of DUREN. vehicles but may necessitate the use of chains on wheeled vehicles. Good cross- country movement may be counted on for no more than eight or nine days per month in the prairie lands during this period of the year. VILLE RIDGE

The VILLE RIDGE is a long (25 miles), narrow (3-5 miles), southward rising promontory with summits 100 to 250 feet above the surrounding countryside. Sur- face soil type is clay loam with sand loam along the flanks of the ridge, but the overburden is rarely in sight due to extensive surface coal mining. The mine pits, dumps, and spoil heaps, and the great number of industrial buildings effectively limit vehicular movement to roads. Scattered mixed and broadleaf forests are found throughout the ridge and are indicated on the map. Crushed rock is available in the mine dumps. Several coal-driven power generating stations are located here. The ridge area is unfit for airfield sites because of mines, industrial towers, buildings, woods, and so on. . -ain -

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Figure 71. Natural terrain features. //'- x -5'w

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