i!AY 4 1927 c N\:;{; ,

• F or Official Use Only 0. N. I. Publication No. 32

• GERMAN SUBMARINES

IN Question· and Answer

NAVY DEPARTl'vIENT OFFICE OF. NAVAL INTELLIGENCE J UNE, 1918

WASHINGTON GOVERNMENT PRINTING OFFICE 1918 I. D. l l i5

GERMAN SUB i\1 ARINES

QUESTION AND A:\'SWER

NAVY DEPARTMENT, O FFICE OF NAVAL INTELLIG ENCE, Washington, May £5, 1918. This pamphlet is only intended to give a geo·eral idea of the characteristics and tactics of German submarines. It is a reprint of a pamphlet published by tbe British Intelligence Department and is for tbe exclusive use of commissioned officers of the United States Navy. It is APRIL, 1918 not to be shown to other persons.RooEn WELLES, Captain, U.S. Navy, Director of Naval Intelligence.

NAVAL STAFF INTELLIGENCE DEPARTMENT INDEX.

Question ::So. :\ ppearance...... 6, 7, S, !J, 10 Areas of activity...... 20 Armament...... 12 Armor...... 48 Bombs, effect of...... 49 Characteristics ...... 2, ~. 4, 5 Charging battery...... 15 Color...... l l Cruiser submarines (including neutschhmds)...... 2, 7, 12, 1~, 1-J, 20 Cruising speed...... 14 Depth charges, effect of...... 49 Depth, maximum...... 1S Depths when submerged...... 17 Distance in one minute submerged...... 31 Diving time...... 19 DoYer Straits ...... 21, 25 Endurance, surface...... 1~ Endw·:mcc, submerged...... lii Fair Isle Channel...... 21, 24 Hydrophone pursuit...... 44 Ilydrophones in submarines...... 45 Lying on the bottom ...... 41, 42 lllioe laying (see also under "U " mine layers and "U. C." boats) ...... 38, 39 Mines, colors of...... 40 Navigation ...... • -•. • • • •• • · · · · · · 37 Night attack ...... --• • - • • --- · • 3,1, 35 Numbers operating ...... - 22 Periscopes ...... • • • • -• • • •• · · 32,33 Radius of action, surface ...... 13 (3) 4

tlll<'~tion ~ll- }6 Radius of action. submerged .. - • • - · · · · · · · · · · · · · · · 11 Recognition mark ...... ••• - · · · · · · · · · · · · · · · · · ·· ., •>'' 1 GERMAN SUBMARINES IN QUESTION Routes ...... ••••··············· - · 4·; Searchlights ...... • • • • · - · · · · · · · · · · · · ·· · · · · ·.; H 15 AND ANSWER. Speed ...... - - • - - • · · · · · · · · · · · · · · · · · ·-, '.1:1 Statical diving ...... -... - · · · · · · · · · · · · · ·· · ... ·_- .;~ ., -H . .,,, -'. -"9 Tactics ...... • • · · · · · · · · · · · · - ' ,1s 1. What are the principal types of German Torpedo firing range ...... • • • · · · · · · · · · · · · · · · ;O submarines 1 Turning circle submerged .. - . - · · · · · · · · · · · · · · · j· ·.~ :t .t, 5 (a) Cruiser submarines, T ypes ...... ·· ...... , •> . ,-,H 1,.-- "0 including converted 1 3 "U" b ts · · · · · · !?, S, l-, '' ' - ·>O mercantile (Deutschlanconning tower 12 are double-hull boats, but breadth, and, in surface trim, dnrn· 11 ½ to a point, as there are no means of 17 is vulnerable feet. Maximum speed on :--urfac•p 1-t} to shutting it off from the inner hull. There are knots· submcrO'ed S to 10 knot:--. also 2 survivors of an earlier class of 15 small ' 0 "U. C." boats, carrying 12 mines only. 3. What are the "U" mine layers? . 1 1 f .. c·,· ho·lf...; ()f the various They are u specrn c nss o . ' __: · ) 6. What is the appearance of 1 which there ,vere orirrinalh- 10. Yiz, 1 ' t( typest t, • . l 1· · 0 tor- U 80 ca-rrmnO' 36 min<'s nnd, m n< < 1twn, - . Photographs of various types of German sub­ • • . t('C(•-;:,;f lll, ' "-"-J ~o st edoes. Thev have not lwen yr1., · • marines will be found in 0. N. I. publication P ► • Th·,,· hn, c 1. These enable the various types to be and only 5 of them now rcmam. t. . . , No. only a single hull and al'<' slo"· ho,it.:--. <'l'lll:--;'t distinguished. generally at about 6 knots, and only cnpi_i ; ~ 7. What is the characteristic appearance of of 10 knots on the surface nnd ' knots :--ll ) a cruiser submarine 1 merged. No details are available of the cruiser type at sea. 4 What are "U. B." boats 1 . proper, as none of these vessels is yet • . 11 .. ~tnb, lnrgei The Deutschlands (converted mercantile There are 3 classes, viz, ~ma t o,i. · 1 tt<'r · Tlw n · ' type) are distinguished by their high freeboard coastals, and small ocenn-gomg. crou:,; . 1 mo~t nun1 and very large guns (5.9 inches), one before which. are the most recenf, nn< · . _ f t in t J (l;) re and one abaft the conning tower. class are double-hull honts n1 )Oll t di,r ' I t l ' 'l bk .() appearan;ce of length, and are suppose< 0 >t • :-:ur- 8. What is the characteristic . ' . f · . 'f)l'f't 1 (ltl with great rapHhty. ~ nx11num :-.. a "U" boat 1 face 13 knots, su bmcr2:cd S knot~- t . of Long flush deck rising toward the bows, ._, l ll 1ion :--, The coastal classes nrc single- HI straight stem, conning tower midway between lower speed and inferior nrnrnll1«' 11 t · bow and stern, usually with steps at different levels. Two conspicuous guns mounted well 5. What are "U. C." boats? and one 16·> fret. Ion~· clear of conning tower, one before They are mine layers aho_ut J- J' .,,·nrd ttil><':-- 101 carrying 18 mines in 6 nrt1cn I 8 show only on sighting their own aircraft. It abaft it. Some of the later boats lrnve n. consists of a white ring, n.bout 12 inches broad net cutter at the bow. and about 4 feet in diameter, fitted on tho dock "U" mine layers are shorter, have a rounded forward. Bon.ts of the Fln.nclcrs and Medi ter­ bow and carry one gun only, which is abaft the ranean flotillas do not carry this mark. conning tower. 12. What armament do the various types 9. What is the characteristic appearance of carry? a. "U. B.'' boat 1 One gun only mounted close before the Co1we~·tcd mercantilcs (Deutsch.lands) carry two 5.9-mch guns, one forwnrd nnship bow with slight overhang, and a very high "U" b oa t s mostl y carry one 4.1-mch· forwn.rd conning tower rising vertically from the deck and one _22-poundPr a.ft, but n. few boats carry "U. n on the fore side. Earlier B.'s" have two 4.1-mch, a few others one 4.1-inch (for­ rounded bow and are much shorter. ward) or t,vo 22-poundcrs. They ha.ve 4-6 10. What is the characteristic appearance of torpedo tubes, 2 or 4 in the bow and 2 in the a. "U. C." boat 1 stern, and they· usun.lh- carry 8-12 torpedoes. Raised forecastle, with gun in the dip between "U" mine lavers ca~rY o~e 4.1-inch abaft the this and conning tower. Net cutter at the conning tower,~ 2 deck~ torpedo tubes (1 bow and 1 stern), 2 torpedoes, and 36 mines. bow. Stern awash. "U• B". b oats carry one 4.1-mch· or one 22- 11. What color are German submarines pounder forward; earlier classes 2 tubes (bow) 1 painted, and do they carry a recognition mark and 2-6 torpedoes; later class 5 tubes ( 4 bow, A dull dirty gray color is usually adopted for 1 stern), and 10 torpedces. the hull. In the Atlantic and North Sea the ''U. C"b. oats carry one 22-pounder forward, deck is painted black; in the :Mediterranen,n 3 tubes, viz: 2 bow (deck) and 1 stern, 4-6, it is sometimes painted dark blue. torpedoes, 18 mines. All submarines operating from the German 61963-18-2 Bight carry a recognition mark, which theY r' 11 hours. In ca.so of radius of action of for long periods, up to 48 -13. What is the extreme run submerged do they actually emergency· a submnrinr could submarines, and how long 12 hours, say at 8 lnwts for:? hours, 5 knots for remain out? 48 hours. 4 knots for :24 hours, or ~ knots for mercantile (Deutschland) <"ln::-~. run­ Converted On service. however. sh(' wonld avoid 6 knots; "r" boats, s,ooo to 17,000 miles at her batteries right down, n.nd would come knots; Inter "F. B.' · and ning 10,000 miles at 10 surface to rPclrnrgr them before the b miles· at S knot~. to the "U· •C" oats, about 6,000 of these periods. class remain out about expiration Converted mercantile Charging is done by the Diesel engines, "U" boats from 20 to 30 dnys. motors 3 to 4 months; which ca.n be used to driYr the electric "lT'' mine lavers gcnPrn.llv !i•:..~; procectling say 25 days; as dynamos while the submnrinc is .,,U. B." boats fr01~ 14._ to 24 ~ day:.;; later on the surface. cluss from 7 to 1-:1: di1,ys · "r. (' ... sub­ "U. B." coastal Submarines on sen~icc rnrely remain in the North Sen a.1i'periscope draft: that is, at the depth just at which the fully ext.ended periscope 15 long can a submarine run sub­ is about • How reaches to the surface. This depth merged? U. B." 45 feet for" r" boats, 38 to 39 feet for" 11 short . At her maximum speed. 011lv for t 1 · · 1me ' fr om to 2 hours, but at slow speed •) 1:2 1'-'

and "U. C." types, reckoned to the bottom of 20. What are the principal areas of activity the keel. in home waters and the Atlantic ? When cruising submerged, submnrincs The principal areas of uctivit:-· (s\.pril. HHS) usually proceed at depths between 66 and Sl are the North Sea, Channel. Irish Seu, and feet, except in very heavy weather, when they approaches to Channel and I rish Sea. g~ to over 100 feet, or when expecting attack In the North Sea, operations arc carried out with bombs or depth char()'es when they dim 1 by "U. B." and" u. C." boats only. to about 150 feet, if the cle1~tl1 of water p~rmits. In the Channel) there arc usuallv. se,eral 18. What is the maximum depth to which "U. B." and "U. C." boat;; of the Flanders submarines can dive? flotilla, which sometimes go as far as the Bay All modern German submarines are tested for of Biscay and Irish Sea, and, at the western a depth of 197 feet, but for short periods they end, possibly one or t,\·o " u•· boats. Thr can go deeper. Cases are known of boats areas of activity vary, but the eastern por1ion havin~ dived to 250 to 300 feet without injur_\·. is used rather for passage, anLl the centrnl and F or lymg on the bottom they do not ordinarily west for actual operations. choose localities in which the depth exceeds As regards the other areas, in good ,\·cathcr

164 feet. the favorite huntinot:>" ()'rounds for " C ·• boats are tho two approaches to the Irish Sea and the 19. How long does a submarine take to dive? western approach to tho Channel. In the win­ _In an e~cient boat, proceeding " ·ith both ter months 1917-18 there was considerable Diesel engmes, periscope draft (see 17) can be submarine activity in the Irish Sea. This r~achecl in 1½ minutes from the order being activity may be repeated at an? time, but more given ~o dive. If the boat is proceeding wit.h particularly in bad weather. "u. B." and o~e Diesel engine and one electric motor run­ "U. C." boats also operate in these areas. . nmg for propulsion (as is frequently done in Mine laying su bmarincs usually lay the1r patrolled areas), the time taken will be even mines in the vicinity of the coast or of sea less. If the submarine is O'oing deeper, the marks, and, having done so, generally proceed furth er d'iv e w1·11 be at the rate° of about a foot to operate, like the other boats, with toq)e­ a second. does and b!nmfire I against commerce. r 14 15

Converted mercantile submarines (Df'11 /., c7· ­ 24. Do submarines pass F a ir I sle at any par­ land type) ha,e hitherto worked entirch· nu,­ ticular time of tide? side home waters, mainly off the west· co 11 "t Apparently not, but there seems to be a ten­ of Spain, westward of Gibraltar, and off the dency to puss in the afternoon or at night. Azores, Canaries, and Cape Verde Island:- : also off the west coast of Africa. 25. Do submarines pass Dover at any par­ ticular time of tide? 21. By what routes do submarines leave and It is believed that they prefer high ,rnter return t o the North Sea? slack at night, but they ha,e also been found Submarines proceed either northabout round lately (March, 1918) trying to pass through the Shetlands or through Fair Isle Channel. <>r quickly on the smfuce in the mist at earl~­ else ,ia the Straits of Dover. The larger bonr:­ dawn. have recently (April, 1918) preferred to pru­ ceed northabout. 26. What are the tactics of a submarine attacking a merchant ship or convoy? 22. Can you give a rough idea of the number The submarine will first try to reach a posi­ of submarines operating simultaneously? t ion ahead of her objecti,e. a\.fter that her tactics will vary according to circumstances. . The number varies O'b reatl.Jv J· a rotwhb avcra Oa e 1s 3 converted merc:111tiles, 10 to 12 " "C ·, 27. Do submarines work together or in any boats (in the Atlantic, etc.), 5 "U. B." and 0 formation? ~ "UC"b• . oats m· t I1e North Sea, and about G "U. B." and 2 "U. C." boats in the Channel Submarines work singly :1.nd inclepenclontly. and Atlantic. t~1ough they may occasionally cooperate for a time in a particular area. 23. Going northabout, do submarines use the Minches? 28. At what range do submarines fire their t orpedoes? They occasionally pass through the Minches, but usually go west of the H ebrides. When attacking single ships, German sub­ marines endeavor if possible to dose to a ran()'e ?f 300 yards to fire a torpedo. When atta.cl;;::­ mg a convoy, they fire at ranges between 500 and 1,000 yards. lG le . do after attack? h t do submarines . 33. Have submarines more than one peri­ 29. W a . ' · 11 llH' direction of t,he1r scope? The,· turn ,l\\ a) I ·r 'ble to obser,o . lc·n-or J poss1 . t tf neccs- Yes : all modern subm:1.rincs h:1,·c two. ,111d " r crc>t' s stern. P IH ,. cl fi1·c "t10ther f " ,.., I I o t an " many have t I1re e pm: 1 scn {)CS • but. 0 111'·. t Ito n'sllll of t 10 s.1 '11 - divCI t,o fl. b,111 t J 50 eet a o-oocl· "1LrY: t,ltcn the:· t~suilL j ll for some J;j minutes. on: of these is used n.t, a time. ,mcl onl~- one. till', c ep i - • . d . t as a rule. is fi.ttetl for use ag11.ins t, 11.irc:rnft. a nd procccf .1 ·- it continues . 1 • } Jl O'Cl' I put::,ll t ack at night ? . , turning circ e 34. Do s ubmarines at 01 o ,., s 30. What is a submarine Subm:.wines now :tttack at nii!ht a lmost as frequently n.s hy cln.y. D uring F ohrnary. 191 , submerged.? f . ''U'' bo,•.ts :weI --'NO A] I t '30 ,·ards o1 - C .. in home waters :30 n.tt,acks were made b:•, d:,y '. 1. )Ot -:1., • , . r types. - ... L B -" n nc 1 v . . and 43 b,- nio-ht . Of the -1:; ,it.tucks, :25 wore Yards fot · bmarine g0 in moonlight Tho nrnjoriLy of total attacks d ·stance w1· 11 a SU • in 3 1, W hat 1 6 7 were mn.dc toward ni~htfall, h otwecn 5 nncl minute submerged. . n would be 233 p. m. one I dis t n.ncc 1 u . t, ) \_ t - J-r10ts t, LC d I)Cr m 1nu e. .! I '- t ·- 33 \'ll,l' S 35, Are night att acks made on t he surface? cl . (One ]m(I - • . shown in ,·ar "· • ope 1s Yes, almost ahvays , excep t in bright moon­ d 'stanc light. • 32. How much of a penscd at what • ~ cl how often; an her limits fo r subma­ attack a~ ope be seen ? c1·t·ons of wind 36. What are t he weat a pensc . I con t I rine work ? can . r e11tlJ w it 1 . b ' il. submn- Thjs van es. g In n. n a ttock .} . . on n The worst conditions for submarine opera­ ind light. ff Dungeness, r.nd sea i I ? l 101 8, o . o was seen tions are given by a calm sea, and if, in addition, 1 \fa.re L - , I pcnscop f 01 - do1· escort, t 10 tl1e por t bow o ~here is a long swell running, it becomes almost rinc 0 "<' un • •s on t, . con,oJ O ·nrds on' a . I above wa c1, unpossible for a submarine to attack unseen. b t 1 00 ) . l 2 me 1es . f . 7 n ou . . - s howing