MHl FM 5-15 42opy3 . s.Ct47qJ /fon- WAR DEPARTMENT ENGINEER FIELD MANUAL FIELD FORTIFICATIONS ,_ ! FM 5-15 ENGINEER FIELD MANUAL FIELD FORTIFICATIONS Prepared under direction of the Chief of Engineers UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON: 1940 For sale by the Superintendent of Documen s, Washington D. C. - Price 45cents WAR DEPARTMENT, WASHINGTON, October 1, 1940. FM 5-15, Engineer Field Manual, Field Fortifications, is published for the information and guidance of all concerned. [A. G. 062.11 (730-40).1 BY ORDER OF THE SECRETARY OF WAR: G. C. MARSHALL, Chief of Staff. OFFICIAL: E. S. ADAMS, Major General, The Adiutant General. IT TABLE OF CONTENTS SEOUrON I. GENERAL. Paragraph Page Definitions _ 1_ 1 Employment _ ._.______. _ _.___-. 2 1 Execution _-_--.- __I__-__......__ .__ 3 2 Nature of work ---_-___.-_-__-_-_-_-. 4 2 Effectiveness against projectiles and bombs--__.. ...... _._._________- 3 Natural conditions affecting design and location--. _.__._.__.__-__. 6 4 Use of existing terrain features...-. 7 5 11. TERRIN APPRECIATION. General _____-- _-- _-- _-- _-- ___-_- __- 8 6 Factors ,_..........______ ....- 9 6 Compartments ---- -_---- ------ -_. 10 8 Influence of corridors . .......11 12 Influence of cross compartments --- 12 20 Aids to study of terrain.....--.------ 13 20 m. ORGANIZATION OF THE GROUND. General --.... _. _____ ___.__.. 14 21 Use of hasty fortifications------------ 15 23 Use of deliberate fortifications _____.- 16 25 Battle position -------------------- 17 25 Platoon defense area -_._.. ......18 29 Company defense area .------------- 19 30 Battalion defense area .… .....20 ..... 31 Regimental sectors -.. .............21 35 Additional organization -.-.-- __.____ 22 36 Artillery support __-____ ___._ .__-. 23 36 Outpost area _---------------------- 24 37 Reserve battle position .-. 25........... 41 Switch positions .---------------__._ 26 42 IV. EFFECT OF PROJECTILES. General- _----_----___--______ 27 42 Infantry weapons .-............__. 28 43 Artillery and aircraft .-.- ........... 29 45 V. TENCHES General -___---- __-- _-__ 30 60 Trace, tracing, and profile_-I-_ __:__ 31 60 Necessity for standard types_-_.---. 32 61 Classification ---.-. __.…___.... ___ 33 61 Hasty ------------------------------ 34 63 Deliberate- .-............ 35 68 Drainage- _------------------------ 36 87 Revetments .-..............._._ 37 92 Breastworks- .------ 38 103 Accessories… ------------------------ 39 105 m TABLE OF CONTENTS SECTION VS. OnSTACLES. Paragraph Page Classification.--.............. 40 117 Basis of location, design, and con- struction . .................... 41 117 Barbed wire ------------ - 42 118 Abatis ------------------ - 43 149 Inundations --------------------- 44 152 Underwater ------------- - 45 153 Tank ------------------- - 46 157 Summary ---------------- - 47 157 VII. EMPLACEMENTS. Infantry weapons... ..---.-.....48 158 Artillery --------------- - 49 188 Antiaircraft mat6riel ........... 50 201 V111. PaOTmCTED S-ELTERS. Classification ------------.-------. 51 206 Choice of type -..---. ---. 52 209 Overhead cover -----------.------. 53 213 Standard construction materials -_ 54 219 Surface ---------------- - 55 220 Artillery ammunition -------- . 56 225 CUt-and-cover.----------------- 57 226 Cave ------------------- - 58 240 Drainage ---------------- - 59 276 Ventilation .. ...60 ......-278 Circulation of fresh air .--------. 61 278 Gasprooling ---------------..--. 62 279 Air supply during gas attack .----. 63 282 Floor space ------------- - 64 283 Time for construction ----------. - 65 284 IX. SUMMARY. General ----------------- - 66 286 T'errain appreciation -------------. 67 286 Organization of the ground ------. 68 287 Effects of projectiles ---------.---- 70 287 Trenches ------------ -7--------.. 71 287 Obstacles ---------------- 7---2 - 289 Emplacements. ... ......----...... 73 290 Protected shelters.-------------- . 69 291. General rules for execution of field works -..--.--..-.-..... 74 ..292 IV FM 5-15 ENGINEER FIELD MANUAL FIELD FORTIFICATIONS (The matter contained herein supersedes chapter 2, part two, Engineer Field Manual, volume II (tentative), June 25, 1932; TR 195-5, October 1, 1926;: TR 195-50, February 20, 1929; and TR 1195-65, January 28, 1926.) SECTION I GENERAL U 1. DErNITIONS.-Field /ortiflcations are works constructed by military forces in combat operations to increase natural defensive strength of a locality. They are of two general classes- a. Hasty, constructed when in contact or about to make contact with the enemy and consisting generally of such fox holes, open weapon emplacements, and simple obstacles as the situation permits. b. Deliberate, constructed out of presence of the enemy or developed gradually from hasty fortifications as a result of long occupation, and consisting generally of such standard trenches, covered emplacements, obstacles, etc., as the situa- tion requires. * 2. EMPLOYMENT.-a. Defense,-Field fortifications are used in defensive operations to- (1) Fortify any position not protected by permanent forti- fications. (2) Supplement permanent fortifications. (3) Provide local security for isolated installations such as coast defense guns. b. Offense.-In offensive operations they are used by- (1) Any portions of the force assigned defensive missions, thus increasing their defensive strength and thereby releas- ing other troops for the offensive. (2) Attacking troops making a temporary halt, thereby Increasing their resistance to counter attacks. I 2-4 ENGINEER FIELD MANUAL c. In general, any occupied position should be protected by field fortifications whether in preparation for defensive or in connection with offensive combat. However, the primary use is in defense. · 3. ExtcuTroN.--a. In general, field fortifications are laid out and constructed by the troops occupying them. b. In divisions, corps, and armies the unit engineer assists in preparation of plans and in technical inspections to insure carrying out such plans. It is seldom that small units have engineer assistance in the planning or laying out. c. Primary duties of engineer troops in execution are- (1) Supply of tools and materials. (2) Execution of works of general use such as command and observation posts, aid stations, etc., for higher units, main communications for supply and evacuation, and water supply facilities. Engineer troops may also assist other units in execution of works for which engineers are better trained and equipped than are the other troops, such as large shelters, obstacles of special nature, special works for drainage, and demolitions. d. Rear positions usually are planned and laid out by the unit engineer under general instructions from the com- mander. Engineer troops assisted by reserve unit and labor troops, and civilian labor if available, usually execute these works. * 4. NATURE OF WORK.-a. Work of fortifying a locality con- sists generally of the following tasks, listed in the order of importance most frequently applicable: (1) Hasty.-The general rule is first to concentrate the bulk of the force on those things which most increase defensive strength of the position. (a) Providing camouflage, limited generally to selection of positions affording natural cover or ease of concealment. (b) Clearing reasonable fields of fire for flat trajectory weapons. (c) Digging open emplacements for machine guns. (d) Digging fox holes (small pits for individual soldier). (e) Erecting obstacles, principally wire entanglements. (i) Digging shallow trenches connecting fox holes when time permits. 2 FIELD FORTIFICATIONS 4-5 (2) Deliberate.-The general rule is first to concentrate as much of the force as is necessary on those things which re- quire the longest time. (a) Adequate communications. (b) Providing shelter for those working on the position. (c) Providing camouflage of important installations. (d) Constructing splinterproof or shellproof observation posts. (e) Constructing protected shelters for troops, command 'posts, aid stations, etc. (f) Constructing splinterproof or shellproof emplacements for infantry supporting weapons. (g) Constructing standard fire and communication trenches. (h) Constructing artillery emplacements. (i) Constructing obstacles of all types, including antitank obstacles. b. In both hasty and deliberate fortifications, the above tasks are undertaken concurrently so that the position is fairly well coordinated for defense at all times. Provision for camouflage must be made before work is commenced. Camouflage is then carried on continuously throughout the work so that as much of the position as possible is concealed from the enemy no matter when he observes it. c. Hasty fortifications are developed into deliberate forti- fications by deepening and extending trenches, strengthening obstacles, adding protected shelters, etc. This development normally is a continuing process, its extent depending prin- cipally upon length of time the position is occupied. As engi- neers may have to assist in development work, they should be familiar with both hasty and deliberate fortifications. d. Breastworks and surface shelters are used in place of trenches, dugouts, etc., where natural conditions such as high ground water level or rock prohibit normal excavation. · 5. EFFECTIVENESS AGAINST PROJECTILES AND BOMBS.-a. Trenches and open emplacements properly constructed pro- vide effective protection against all small-arms fire, artillery projectiles up to 4 inches in caliber, and fragmentation bombs (usually 20 pounds), except direct hits. Such works can be 3 5-6