Nr. 2127

Geheim!

Handbuch

für U-Bootskommandanten

(U.Kdt.Hdb.)

1942

Nachdruck 1943

(Deckblatt Nr. 1-11 und handschriftliche Berichtigungen eingearbeitet)

Oberkommando der Kriegsmarine

M. Dv. Nr. 906

Table of contents

Paragraph Page

1 – 2 Preliminary notes........................................... 7

Section I.

General.

3 – 18 A. Essential characteristics and

uses of the U-Boat ...................................... 9 – 12

19 – 64 B. Avoiding detection by the enemy ................. 12 – 23

21 – 45 I. How not to be spotted ............................ 12 – 17

46 – 54 II. How not to be located by

listening equipment ............................... 18 – 19

55 – 64 III. How not to be located by ASDIC ........... 20 – 23

65 – 74 C. Means of communication of the U-Boat ....... 23 – 25

75 – 90 D. Limitations of the U-Boat ............................. 26 – 27

Section II.

The underwater torpedo attack.

91 – 104 A. Fundamental rules for underwater

torpedo attack ................................................. 28 – 31

105 – 124 B. Preparing for the underwater

torpedo attack .................................................. 31 – 35

125 – 140 C. Carrying out the underwater attack ................ 36 – 38

141 – 170 D. Types of the underwater torpedo attack .......... 39 – 47

142 – 145 I. Attack with the aid of the torpedo

fire control system ................................... 39 – 40

146 II. Direct bow attack ...................................... 40 – 47

147 III. Direct stern attack ...............................,..... 41 – 42

148 – 149 IV. Gyro angled attack .................................... 42 – 43

150 1. 45° gyro angled shot .................... 43 – 45

151 – 170 2. 90° gyro angled shot .................... 45 – 47

171 – 174 E. Use of torpedoes .............................................. 47 – 48

175 – 194 F. Proceeding after underwater torpedo attack .... 48 – 51

Paragraph Page

Section III.

The surface torpedo attack.

195 – 218 A. Fundamental rules for the night

surface attack ................................................. 52 – 57

199 – 206 I. Danger of being sighted ....................... 54 – 55

207 – 213 II. Danger of being located by

listening equipment ................................ 55 – 56

214 – 218 III. Danger of being located by

ASDIC ................................................... 56 – 57

219 – 226 B. Preparation for the surface night attack ....... 57 – 59

227 – 234 C. Carrying out the surface night attack ............ 59

235 – 245 D. Proceeding after night surface attack .......... 60 – 61

Section IV.

246 – 269 Proceedings against enemy defense

and pursuit ............................................... 62

250 – 253 A. Proceeding against passive sound-location .... 62 – 63

254 – 265 B. Proceeding against active sound-location

(ASDIC) ......................................................... 63 – 67

266 – 270 C. Proceeding against air-planes ........................ 67 – 68

Section V.

271 – 279 U-Boat as a gunnery vessel ................................. 69 – 73

Section VI.

280 – 289 U-Boat as a mine-layer .......................................... 74 – 75

Section VII.

U-Boat war against merchant shipping

290 – 300 A. General ........................................................... 76 – 77

301 – 309 B. Stopping the merchant vessels ........................ 78 – 81

310 – 339 C. Proceeding with convoys ..............,................. 81 – 90

Paragraph Page

Section VIII.

Wolf packs – reconnaissance and attack

340 – 341 A. General ........................................................ 91

342 – 348 B. System of command ..................................... 91 – 92

349 – 374 C. Types and patterns of the wolf pack ............. 92 – 97

375 – 390 D. Proceeding in the operation area before and

after contact with the enemy ........................ 97 – 100

Section IX.

Use of torpedoes.

391 – 395 A. Use of torpedoes ........................................... 101 – 102

Section II.

The underwater torpedo attack.

A. Fundamental rules for the underwater attack.

91. The object of the underwater attack is to discharge a torpedo with

the certainty of hitting, but without warning, and at short range. The

shorter the distance between the U-Boat and the target, the more reliable the

assessment of the speed and angle on the bow of the enemy. The torpedo

attack at short range is the most advantageous also because not even

important miscalculations affecting the launching of the missile can take

effect to any appreciable extent, on account of the short course of the

torpedo, and by reason of the fact that any counter-action on the part of the

enemy - for example, a change of course (evading), if the U-Boat or the

torpedo is spotted - comes too late.

92. The shortest distance to the target is defined by the distance needed

to set the torpedo on its course at the appropriate depth and by the safety

range, that is the distance of the U-Boat from the point of detonation of the

torpedo. No torpedo attack should, therefore, be carried out at a range under

300 m.

93. Invisibility during the attack is made possible by the judicious,

invisible use of the periscope, the bubbleless launching of the torpedo, and

the absence of bubbles in the track of the torpedo.

94. The efficiency of the listening and sound-locating equipment of the

enemy is dependent on the state of the sea, the nature of the water

, the

speed of the enemy (see Section I, B, II and III), the attentiveness of the

personnel, and other factors. The danger of being located by listening or

sound-locating equipment should not be allowed to prevent the carrying out

of a fatal attack at short range.

95. When attacking ships cruising with low and medium speeds, at

close range, it ballistically advantageous to fire at an angle on the bow of

90°, as errors estimating the angle on the bow will in this case have the least

effect; besides the speed of the enemy can be most accurately estimated at

this angle on the bow. If the range is longer (over 1,000 m), and the target is

traveling at a high rate of speed, an attempt should be made to launch the

torpedo at a smaller angle, say, 60°.

96. Because U-Boat is not equipped with the range-finder, the

determining the target course data by means of the rate of change of bearing

method

is not possible. The target data: angle on the bow, speed and

distance are determined by plotting or by estimating during the approach

for the attack. The estimation of the target course parameters by eye and

using mono-ocular periscope is hard and requires many practices.

97. The estimation of the angle on the bow is the easiest when the U-

Boat positions itself forward of the beam. If the sun is behind the target, the

assessment of the angle on the bow is difficult.

98. The speed of the enemy can best be estimated from the position at

the abeam of the target. In estimating the speed, attention should be paid to

the stern wave rather than to the bow wave, because, if the shape of the bow

is narrow (pointed), the bow wave is visible very slight. In addition, the

stern wave is more difficult to camouflage

In estimating the enemy's speed, his course in relation to the direction

of the waves, as well as the change of bearing and angle on the bow, should

be taken into consideration.

99. Every available opportunity should be taken for practicing range

finding (i.e., estimating the range). In estimating ranges, conditions of

visibility play an important part. In clear weather and with the sun behind

one's back, the distance is liable to be underestimated, in poor visibility,

against the sun, in conditions of twilight (dusk and dawn), and by

moonlight, to be overestimated.

100. Favorable conditions for attack:

a) With the sun behind: The shooter (the officer in charge of

the discharging of the torpedoes) is not dazzled, but can

clearly see the sharp outline of the target. From the enemy

ship, the periscope, raised no more than is absolutely

necessary, is not to be seen among the reflections of the bright sun in

the water; and also a trail of bubbles can not usually be seen until it is

too late.

b) From the windward side: Fundamental rule: the periscope should move

with the waves. The waves, coming from behind, always wash over a

periscope which is in the right direction and in a low position; and the

splashes and spray water created by the periscope are not easily to be

spotted. In addition, the enemy look-out to windward, especially in a

strong wind or in heavy rain, meets with difficulties.

As regards the windward side, if the wind is moderate, there is

exceptional case, when torpedoes are discharged from the stern – the

U-Boat is moving with waves and the torpedoes are launched into

leeward side of the target – the movement of the U-Boat nearly

compensates waves. Whereas to windward - driving against the sea –

the periscope may cause conspicuous splashes even when the U-Boat is

traveling at low speed. In a keen wind, however, the windward side

is also more favorable for the stern launching of torpedoes, because the

enemy, as a matter of course, keeps a better lookout to leeward, and is

easier to observe.

c) Wind 3 to 4 and sea state 2 to 3 are most favorable for making the

attack, because the waves wash over the low-lying periscope, without

interfering with the view of the target, while the depth-keeping at

periscope depth is not difficult.

101. Unfavorable conditions for attack:

a) Heavy seas or swell: it is difficult to keep the U-Boat at the right depth

for attack, especially when the attack has to be carried out against the

waves. According to the qualities U-Boat depth-keeping, this will soon

put a limit to the possibilities of underwater attack (see Section I, D,

Paragraph 78). In a rough sea, an attack in a direction parallel to the

waves is more likely to succeed (mostfavorable for the depth-keeping at

periscope depth and the depth-keeping of the torpedo).

b) Sea as smooth as oil: The slightest ripple even of the low periscope is

noticeable, and easily observable by the enemy. Exceptions: bright sun

behind; conditions of twilight and moonlit nights.

c) Attack with dark thunderclouds in the background; even the most

efficiently camouflaged (painted) periscope will then appear white

against the dark black clouds.

d) Against the sun: the estimation of speed, angle on the bow and distance

is considerably more difficult; besides which, if the attack is carried out

against the sun, there is the danger of attracting attention by the flashes

of light proceeding from the objective.

102. Free.

103. Free.

104. Free.

B. Preparing for the underwater attack.

105. General rules for the attack:

a) The U-Boat commander should be alert and suspicious on patrol, as

long as there is no target; but everything should be thrown into the

attack.

b) Proceed with care when a target has been found. The attack should be

carried out with tenacious will and steadfastness, until final success

has been achieved. During the attack, situations often arise which

would be a reason for disengaging from the enemy. These moments of

doubt, and these temptations, must be conquered.

c) Never delude yourself by assuming that it is right not to attack on the

instant, or not to hold on the enemy with the utmost determination,

because there may be reason to hope and believe that a better target

will subsequently be found elsewhere. What you have got, you have

got! Do not let such considerations give you the idea of trying to save

fuel.

d) The attack should only be postponed in case of imperative necessity,

for example at dusk - if it should already be too dark for underwater

torpedo launching - in order to be able to carry out a surface attack

after night- fall, with greater safety and a better chance of success.

e) In every U-Boat attack, whether by day or by night, the attempt

must be made to obtain reliable data for aiming the torpedo, by

exhausting all possibilities with care and deliberation (measuring the

rate of change of bearing with the aid of the stabilized azimuth line

angular height of the masts at a given height in the 1/16 scale,

suppressing

the target speed and course on the surface, by day and

night).

Do not attack immediately at random, success cannot be achieved

that way.

f) Do not attack from positions which offer no chance of success. Keep

your head and wait, in order - in daytime, if it is still light enough - to

make a second attack by another overhauling maneuver, or in order to

attack at night.

g) Particularly difficult target for the U-Boat are: destroyers, on account

of their speed and the relativeshortness of the target they offer, and

submarines, on account of their small height (difficulty of range

finding) and their shape above water, which is unfavorable for

estimating their angle on the bow. Consequently, attacks on destroyers

and submarines can only be carried out at short range. No single shots;

salvo shooting.

h) In wartime, one is always farther away from the enemy than one

thinks, especially at night. Hold out then and go near.

Firing at close range also makes for greater safety for your own

boat. In the neighborhood of its own ships the enemy escort will not at

first drop depth charges.

106. As a matter of principle, every underwater attack should be so

prepared and carried out that the launching of torpedoes can take place at

the earliest possible moment. Favorable opportunities of attack may be lost

by hesitating. If conditions allow, the U-Boat should therefore go to meet

the enemy. It is wrong to keep ahead of the enemy and wait until he comes

into range.

107. The commander must be quick and versatile, and be guided by

circumstances in deciding which method of attack is the most favorable, and

will most quickly achieve success. As long as the enemy is in range, the

U-Boat must be in a position to launch a torpedo at any moment, in case

the enemy takes counter-measures, by veering, etc., even if the desired

position most favorable for launching the attack, for example, an angle on

the bow of 90°, has not yet been reached. The commander should never

concentrate rigidly and schematically on a certain desired angle on the bow

and operate with that exclusive object in view.

108. On account of the low underwater speed of the U-Boat, a position

forward of the beam of the enemy is a necessity when attacking underwater.

The initial position for the underwater attack must be the more forward of

the enemy's beam, the greater the distance is between the U-Boat and the

enemy. In normal visibility and normal conditions of attack, the U-Boat

should therefore not dive for the underwater attack until it has reached the

angle on the bow 0° in relation to the general course of the enemy.

109. If the U-Boat is not already ahead of the enemy's beam when the

latter comes in sight, an attempt must be made to reach the required position

at top speed on the surface. The most favorable converging course in

relation to the enemy when overhauling, is always the course perpendicular

to the target bearing, as long as the U-Boat is in a more forward position

than abeam of the target.

110. In taking up the position forward to the beam of the target, the

U-Boat must not endanger its most valuable asset: invisibility. In daytime,

in clear weather, the U-Boat should not therefore be able to see more of the

enemy than just the tops of his masts (look-out on the mast, range-finder in

the foretop, see Section I, B, Paragraph 25).

111. Attention should be paid to the differences in the conditions of

visibility of the various sea areas. Conditions can be encountered in which it

is possible to approach much nearer to a surface ship, without immediately

being spotted, because the air is not always absolutely clear, and the dip of

the horizon is frequently blurred and misty. In the Atlantic, a U-Boat can be

spotted by the enemy as soon as it is lifted by the swell of the sea - as

occasionally happens - even when, for a considerable length of time, the

U-Boat could not previously have been visible from the enemy ship.

112. The overhauling maneuver requires a high tactical skills, its

success is the pre-condition of the following underwater attack,

and therefore the success of the operation. As a tactical masterpiece, the

overhauling maneuver is therefore the exclusive matter of the commander,

and its preparation and execution require his unremitting attention.

113. An effort to take the forward position ahead of the beam of the

enemy at the borderline of visibility during the day, requires a long, drawn-

out and extremely tiring overhauling operation. It is an unceasing "nibbling

at the horizon" - going in again and again as soon as the tops of the masts

get smaller, and sheering off again at once, as soon as they rise higher again.

These strenuous efforts to overhaul the enemy are continued, in the Atlantic,

hour by hour, and can only succeed as a result of unswerving tenacity and

an unchanging, obstinate refusal to let the enemy escape, even when the

U-Boat finds that progress is very slow. Any change of target course or

engine trouble occurring on board of the enemy ship, may immediately alter

the position in favor of the U-Boat.

114. The overhauling maneuver should always be exploited, in order to

obtain the target course data (course, speed, pattern of the zigzag course) by

careful observation of the own course, the target bearings, estimation of

range and angle on the bow at regular intervals of time to make combat plot.

These particulars are almost always more reliable than those obtained while

submerged.

115. The overhauling maneuver and the attack should not be abandoned

even when the bearing shows little movement of the enemy. Do not let the

difficulties wear you down!

116. Free.

117. Whether or not - in view of the low surface and submerged speed

of the U-Boat - an overhauling maneuver in daylight is bound to succeed

depends on the speed of the target and his angle on the bow when sighted. If

the enemy escort is well forward of the ships, or if the enemy has an air

escort, so that the U-Boat is forced to dive both frequently and prematurely,

thus further reducing its already low speed, the overhauling maneuver meets

with an additional serious difficulty. But in this one case also, the U-Boat

commander must show determination and not give up.

118. If the U-Boat is temporarily forced to submerge by the enemy

escort, etc., it must not stay submerged too long. It should always try to

surface again as soon as possible, in order to observe the enemy better and

not to lose valuable time without a good reason.

119. In case of sudden deterioration of visibility, due to squalls of rain,

etc.; stay alert. The U-Boat should submerge, if improving visibility reveals

that it has approached too near to the enemy while the visibility was

deteriorated.

120. When the U-Boat has reached the necessary position forward of

the enemy's beam, that is to say, it stays at opposite course to the general

course ascertained for the enemy (see Paragraph 108), it must move toward

the enemy on the surface and underwater, always in the endeavor to shot

torpedo as soon as possible, before the position changes, i.e., before, for

example, the enemy changes course, in such a way as to fail the attack.

121. Free.

122. Free.

123. Free.

124. Free.

C. Carrying out the underwater attack.

125. When the distance to the target is about 4 ~ 5000 m depending on

the weather and lighting conditions, the periscope should be used

“sparingly”, that is periscope should be raised frequently, but for short time,

just above the surface (the head of the periscopes no bigger than fist),

almost constantly washed over by waves (see Section I, B, Paragraph 31). It

is a mistake to keep the periscope down for longer time when the enemy is

near. In that case the U-Boat is not less visible than during the “sparing” use

of the periscope; but it itself is blind, and is therefore in greater danger.

Consequently, the U-Boat should carry out frequent observations of short

duration; but, in all circumstances, they should be repeated again and again.

126. The periscope should only be raised when the U-Boat is cruising at

low speed. Before raising the periscope, it is therefore necessary to reduce

the speed. Otherwise, if the sea is calm, the wake of the periscope can easily

be seen, besides which the periscope of a U-Boat cruising at higher speed

will cause splashes and a conspicuous feather.

127. If special reasons require that the speed be temporarily increased,

for example, in order to reach a position more suitable for launching an

attack, the periscope must be lowered until the top of it is at least 1 m under

the surface. When the U-Boat is at the periscope depth, the periscope should

not, however, be further lowered to an extent greater than it is absolutely

necessary, in order not unnecessarily to lose time in raising it again.

128. In a calm sea, the propellers of the U-Boat cause a slight ripple

which is visible on the surface. If it is necessary in this case to proceed at

higher speed, the periscope should therefore be lowered, and the U-Boat

should dive to 18 m, insofar as the nearness of the enemy will allow this.

129. Towards the end of the attack, just before the torpedo is launched,

it must suffice for the torpedo shooter, on final estimating the target speed

and angle on the bow, to see only the tops of the funnels and masts of the

target.

130. For estimating the range, the 1½ magnification should be used.

With the 6-fold magnification, no estimation of distance is possible, on

account of the monocular optical system of the periscope.

As a matter of principles the 6-fold magnification of the periscope

should always only be used temporarily, in order the better to observe

details of the enemy ship, as, for example, for estimating its angle on the

bow and speed, but never for the actual attack at close range.

131. At a distance of about 4,000 to 2,000 m, according to the speed

and angle on the bow of the enemy, the U-Boat begins to go in for the

attack.

The following rule of thumb serves to determine, in good time, the

distance of the U-Boat when about launch the torpedo abreast of the target:

When angle on the bow is 5°, the lateral distance from the

target = 1/10, when angle on the bow is 10° = 1/5, when angle on

the bow is 15° = 1/4, when angle on the bow is 20° = 1/3, when

angle on the bow is 30° = 1/2 of the momentary distance

132. The danger of being located by sound location during the attack at

close range must be countered, as far as circumstances allow, by cruising at

as slow a speed as possible, and by absolute silence on board the U-Boat

(see Section I, B, II and III).

133. The underwater attack is also practicable at dawn and dusk, and on

moonlit nights. In these cases, the following points should be observed:

a) Complete blacking out of the conning tower and the control room is

necessary, as otherwise the light is still reflected, to a considerable

extent, in the periscope.

b) The estimation of distances and angle on the bow at night by means

of the periscope meets with great difficulties. The U-Boat may

easily be nearer to the enemy than is supposed.

c) At night, all periscope operations should be undertaken with the

1 ½ magnification, on account of the better light transmission of

the optical system when using small magnifications

d) The observation of the enemy against whom the attack is directed,

and the all-round view in respect of the position in relation to other

nearby vessels, can then be undertaken, in certain circumstances, by

two periscopes.

134. The rare opportunity of attacking an enemy convoy must be used,

by going all out, with all the torpedoes, even in spite of the strongest enemy

escort. One of the convoy's ships should be attacked, and the attack carried

out, by a method suited to the position of the target, in a manner calculated

to annihilate the latter; immediately afterwards a second and third ship

should be attacked where possible.

135. The shape of a convoy is difficult to make out from periscope

depth and at a distance. If the enemy group is a broad one (blunt formation,

line abreast, double line ahead, broken formation) it is advantageous to let

one's self run into the formation from the front, and to fire angled

torpedoes. The advantages of this position in the enemy group are: less

efficient covering and less vigilance on the part of the enemy, and

consequently maximum deliberation in carrying out the attack.

In attacking a pointed formation, the open side is more favorable,

because the chances of a hit are better (the targets overlap). In addition, on

the open side the U-Boat is in less danger of being rammed, and can

therefore carry out the attack with more deliberation.

136. If, during an attack on a convoy, the necessity arises of diving

suddenly to a depth of 20 m, as a protection against escorting ships or

airplanes (i.e., because there is a danger of being rammed or spotted) the

attack must on no account be finally abandoned because of that necessity. In

view of the fact that, when cruising at the depth of 20 m, the U-Boat loses

count of the position in the direction of the attack, it may then in certain

circumstances be advisable to turn away from the convoy, at full speed, and

turn down again with little divergence from the general course of the enemy,

in order to resume the attack from the outside. If the convoy is a long one,

there is then always a chance of getting in a shot at the last ships.

137. Free.

138. Free.

139. Free.

140. Free.

D. Types of the underwater torpedo attack.

141. The ordinary underwater attack is carried out with the aid of the

fire control system. If the entire fire control system fails to function, and in

the case of unexplained misses, the direct bow, stern or angled torpedo

attack is called for. These methods of attack must also be mastered by the

U-Boat commander, and used according to circumstances.

I. Attack with the aid of the torpedo fire control system.

142. Advantages of the attack with the aid of the torpedo fire control

system:

a) The commander is free from the necessity of calculating the

direction of the attack, and of maneuvering on this course, and can

devote his attention entirely to securing a favorable position for the

attack. The only necessity is to get the target into the angle covered

by the torpedoes with the gyro angle as small as possible

b) The possibilities of using the torpedo are considerably greater, as in

case of necessity, the entire gyro angle range of the torpedo can

always be exploited, and the torpedo discharged in any direction.

c) The fire control system takes into account the parallax, so that, if

the firing data are correct, the hitting point usually coincides

with the center of the target.

d) The range can always be read off, and the salvo spread angle and

the turning speed of the U-Boat can quickly be embodied in the

calculation for improving the gyro angle.

e) Difficult and quickly changing situations (high speed of the target,

frequent changes of course) can be mastered by a U-Boat with fire

control system in circumstances in which a U-Boat without fire

control is forced to renounce the torpedo attack because of the

inability of the U-Boat to turn quickly under water.

143. The important difficulty of the torpedo attack with the aim of the

fire control system - and this also applies to every gyro angled attack - is the

accurate estimation of the distance as a basis for the parallax correction. In

case of uncertainty in assessing the distance, more especially in firing at

close range, and during engagements en passant, one should therefore

always endeavor to fire at as small a gyro angle as possible, in order to

avoid missing as a result of false parallax correction values. If the gyro

angle is large, a false calculation of distance, especially of distances under

1,000 m, results in torpedo miss, due to the error of the parallax correction.

144. In view of the fact that the attack with the aim of the fire control

system, when carried out underwater, unlike the direct bow attack, requires

complicated technical equipment with a comparatively large personnel, so

that the number of possible sources of error is correspondingly greater,

careful training of all the operators, and close attention to the equipment, are

a special necessity.

145. If the electric system of the fire control is out of action, do not at

once fall back on the primitive methods of the direct bow, stern or angle

attack, but use to the full the reserve possibilities of the plant (calculator as a

mechanical computing device

). There should be frequent rehearsals of the

procedure to be applied when the electric system of the fire control is out of

action.

II. Direct bow attack.

146. Procedure:

a) determine the target course from its angle on the bow and bearing;

b) estimate target speed;

c) calculate deflection angle for the intended angle on the bow = 90°

at the moment of torpedo launch;

d) put the U-Boat at the attack course.

Attack course =

true bearing perpendicular to the target course

deflection angle, according to whether the starboard or the

port of the enemy is to be attacked

If it is intended to attack with the narrower angle on the bow,

while determining the attack course, instead of the true bearing

perpendicular to the target course, the true bearing respective for

intended angle on the bow, for example 60°, should be used

e) By "flanking" the course (i.e., keeping ahead of, or behind

the direction of the attack), the U-Boat should approach to within

close range, and take up a favorable position (angle on the bow 90°

etc.). In doing is, constant observation of the growth of the target

angle on the bow and constantly repeated estimations of the

distance, while using the periscope sparingly, are a necessity.

f) If the target course has been correctly ascertained, and his speed

correctly assessed, the enemy must set itself at the angle on the bow

of 90° etc. when he enters in the cross-hair of the periscope, which

was set to the previously calculated deflection angle. If this does

not happen, the moment of firing must be anticipated or

retarded, by discharging the torpedo while turning toward, or away

from the target, in order to exploit a more favorable target position.

III. Direct stern attack.

147. The direct stern torpedo attack can only be carried out either when

the position of the U-Boat is ahead of the target, or when, in consequence of

a sudden change of course on the part of the enemy, the use of the stern

torpedo tube is more advantageous than the use of the bow torpedo tubes.

Procedure:

a) if the U-Boat is ahead of the target, it must go to meet him, in order

to carry out the stern torpedo attack. Moving toward the enemy is

better than moving with him, because, in this case, the U-Boat, in

turning away to take up the direction of attack, has less turning to

do to the extent of the double the deflection angle;

b) determine course and speed of the target;

c) calculate deflection angle for the intended angle on the bow = 90°

at the moment of torpedo launch;

d) put the U-Boat at the attack course. The turning speed should be

effected according to the speed at which the target is approaching.

Do not turn too quickly, as otherwise the range becomes too long.

Keep your head!

Attack course =

true bearing perpendicular to the opposite target course

deflection angle, according to whether the

starboard or the port of the enemy is to be attacked.

If it is intended to attack with the narrower angle on the bow,

while determining the attack course, instead of the true bearing

perpendicular to the opposite target course, the true bearing

respective for intended angle on the bow, for example 60°, should

be used.

IV. Gyro angled attack

148. The gyro angled attack has the following important advantages:

a) The U-Boat is able to move more freely in carrying out the attack,

and need not, as it has to do when making a direct bow attack,

approach the enemy almost perpendicular keeping the target's

angle on the bow and the distance under constant observation.

b) The U-Boat does not cross the courses of the enemy's escorting

ships to the same extent as when carrying out the direct bow

torpedo attack.

c) In case of a too-closely developed bow attack, or of sudden changes

of course on the part of the enemy, it is still possible to fire a

torpedo.

d) If the enemy formation is a broad one, the gyro angled attack

affords the best opportunity of attacking several targets on either

side, by allowing one's self to be overtaken by the formation.

149. The gyro angled attack consists mainly of:

1. 45° gyro angled shot;

2. 90° gyro angled shot.

The commander can make use of other methods of gyro angled attack,

if he is able to make the necessary calculations during the attack, without

their having been especially rehearsed, as have the two most common

methods of gyro angled attack.

1. 45° gyro angled shot.

150. Procedure:

a) put the U-Boat at the attack course:

aa) Bow 45° gyro angled shot:

α) Running Fight (Bow of the U-Boat in the same direction

as the course of the target):

Attack course =

true bearing perpendicular to the target course

(45° + deflection angle), according to

whether the starboard or the port of the enemy is

to be attacked.

If it is intended to attack with the narrower angle on

the bow, similarly as during direct bow attack, while

determining the attack course, instead of the true bearing

perpendicular to the target course, the true

bearing respective for intended angle on the bow, for

example 60°, should be used.

β) Engagement en passant (bow of the U-Boat in the

opposite direction to the course of the target):

Attack course =

true bearing perpendicular to the target course

(45° - deflection angle), according to

whether the starboard or the port of the enemy is to

be attacked.

bb) Stern 45° gyro angled shot:

α) Running Fight (Bow of the U-Boat in the same direction

as the course of the target):

Attack course =

true bearing perpendicular to the opposite target

course (45° - deflection angle), according

to whether the starboard or the port of the enemy

is to be attacked.

If it is intended to attack with the narrower angle on

the bow, the attack course is determined in the same way as

in case of other, previously mentioned methods of

attacks.

β) Engagement en passant (bow of the U-Boat in the

opposite direction to the course of the target):

Attack course =

true bearing perpendicular to the opposite target

course (45° + deflection angle), according

to whether the starboard or the port of the enemy

is to be attacked.

b) Set the deflection angle. Turn the graduated dial on the rim of the

periscope by 45° away from the 0° mark toward the target, and then

adjust the deflection angle from the 45° mark to the position of the

target; i.e., if the enemy course is to the left, the deflection angle

must be set to the left of the 45° mark, and vice versa. Points to be

observed: the deflection angle always lies outside the 45° torpedo

angle, when the torpedo, before it turns, travels in the same

direction as the target (for the bow gyro angled attack in running

fights, for the stern gyro angled attack in engagements

en passant); the deflection angle lies inside the 45° torpedo angle,

when the torpedo, before turning, travels in the opposite direction

to the target (for the bow gyro angled attack in engagement en

passant, for the stern gyro angled attack in running fights). In both

cases, however, the deflection angle should always be set in the

direction of the target from the 45° mark.

c) For parallax correction of 50 m

, allow for forward or backward

movement; for the former, when the torpedo, before turning, moves

in the opposite direction to the target (for the bow gyro angled

attack in engagements en passant, for the stern gyro angled

attack in running fights), and for the latter, when the

torpedo, before turning, moves in the same direction as the target

(for the bow gyro angled attack in running fights, for the stern gyro

angled attack in engagements en passant).

2. 90° gyro angled shot.

151. The 90° gyro angled attack should only be used for small parallax

corrections; i.e., when the torpedo, before turning, moves in the same

direction as the target. It is very difficult to estimate the deflection angle for

large parallax corrections, especially when attacking at short range.

Consequently, the 90° gyro angled shot with a small parallax correction

of the target is used:

in running fights in the form of the bow torpedo attack,

in engagements en passant in the form of the stern torpedo

attack.

152. Procedure:

a) put the U-Boat at the attack course:

aa) Bow 90° gyro angled attack in running fight:

Attack course =

true bearing perpendicular to the opposite target course

(90° - deflection angle), according to whether

the stb. or the port of the enemy is to be attacked.

If it is intended to attack with the narrower angle on the

bow, the attack course is determined in the same way as in case

of other, previously mentioned methods of attacks. Instead of

the true bearing perpendicular to the target course, the true

bearing respective for intended angle on the bow,

for example 60°, (or opposite to this bearing respectively)

should be used.

bb) Stern 90° gyro angled attack in engagement en

passant:

Attack course =

true bearing perpendicular to the target course

(90° - deflection angle), according to whether

the starboard or the port of the enemy is to be attacked.

b) Set the deflection angle: turn the graduated dial on the rim of the

periscope by 90° away from the 0° mark toward the target, and then

adjust the deflection angle from the 90° mark to the position of the

target. If the enemy course is to the left, the director angle must

be set to the left of the 90° mark, and vice versa (see also paragraph

146, b).

c) For parallax correction move periscope ...........m backward from

the target.

153. The chief difficulty of the torpedo attack with the aid of the

torpedo fire control system - and this also applies to every gyro angled

attack - is the precise estimation of the distance as a basis for the parallax

correction. In case of uncertainty in estimating the distance, more especially

in launching torpedoes at close range, and during engagements en passant,

the object to be achieved is always to fire at the minimum gyro angle, in

order to avoid misses resulting from false parallax correction values. If the

gyro angle is large, a false estimation of distance, especially of distances

under 1,000 m, results in materially wrong measurements on the target, due

to the error of the parallax correction.

154. Free.

155. Free.

156. Free.

157. Free.

158. Free.

159. Free.

160. Free.

161. Free.

162. Free.

163. Free.

164. Free.

165. Free.

166. Free.

167. Free.

168. Free.

169. Free.

170. Free.

E. Use of torpedoes.

171. As far as the supply of torpedoes allows, several shots, in the form

of multiple discharges

(double or three-fold discharges) should be

directed against worthwhile targets, even at short range, and when the data

calculations are not in doubt. In this case, all the torpedoes should hit the

mark, in order to ensure the annihilation of the target. This means that the

torpedoes should be fired at different parts of the target.

172. If the range is over 1,000 m, or if there is uncertainty as regards the

target course data (high speed of the target), several torpedoes (2, 3, or 4)

should be released on the "fan" pattern. The idea is to make sure of one hit.

It is better to score only one hit than to miss the target with each of several

consecutive shots.

The shots should be spread by the width of the dispersion area in

relation to one shot aimed on the basis of the estimated data (if 2 or 4 shots

are fired, in relation to an imaginary middle shot).

173. If a final shot is necessary to sink the damaged ship, remember that

the number of misses at the kill is proportionally greater than in firing

during the attack.

a) At the kill, steer the U-Boat ahead of the stationary target, with

angle on the bow 90°, at range 2,000 to 3,000 m, and approach

slowly, carefully keeping the course, to find out whether the target

is still making headway. When the change of target bearing has

been observed, the speed of the target should be set on the

torpedo calculator, or the target should be finished off by the direct

bow or stern torpedo attack with torpedo firing control

system switched off. The speed of the target should be taken into

account in determining the displacement of the marking point on

the target.

b) Go in as close as possible, range under 1,000 m. On moonlit nights

and during the daytime, submerge once more and attack underwater

at 400 to 500 m.

c) If, in remote sea areas, an early arrival of enemy defense forces is

not to be anticipated, the final shot should not be precipitated.

Many ships sink only after 2 to 3 hours.

d) If enemy anti-submarine forces are sighted (naval or air), the final

torpedo should be fired at once.

e) In the circumstances described under c) it should be ascertained

whether the target can be destroyed by gunfire, instead of by the

final torpedo. See also paragraph 277.

174. Free.

F. Proceeding after underwater torpedo attack.

175. If at all possible, the U-boat should remain at periscope depth, in

order to carry out observations after the underwater attack, and of

deciding whether another torpedo is needed to complete the destruction of

the target.

Motto: "Better to destroy little than to damage much!"

176. Exploit the position for attack taken up near the convoy, or in the

vicinity of several objectives, for the purpose of discharging several

torpedoes in quick succession at several targets, making use of the

possibilities of the fire control system. It is not certain that so favorable a

position for attack will again be attained. See paragraph 171.

177. If the U-Boat remains at periscope depth after the attack, it will

have the advantage of being able to observe the methods and extent of the

enemy counteraction, besides finding new opportunities of attack. In this

way the U-Boat is also enabled to discover gaps in the pursuing forces of

the enemy, through which it can escape.

178. If there is no further possibility of attack, the U-Boat should leave

the scene of action. If there is a danger of being located by listening

equipment, the U-Boat should then travel at "listening speed"

If there is no danger of being discovered by listening equipment, on

account of interference resulting from sounds proceeding from the enemy,

the U-Boat should leave the scene of action and get out of the direction of

the attack

at full speed.

179. Do not go deep down unless it is absolutely necessary. If you do

so, you render yourself blind and helpless. Consequently, do not dive to low

depths unless the danger threatening from enemy escort vessels in the

immediate neighborhood is real and imminent.

180. If the U-Boat is forced to dive deeper after the underwater attack,

on account of the dangerous proximity of enemy escort vessels, then it

should first go down at full speed in a direction leading away from the

shooting position and the direction of the torpedo. During the first confusion

on the surface after a torpedo hit or during the dropping of depth charges,

the enemy escort will operate neither with ASDIC nor with listening

equipment.

The U-Boat should cruise at "silent running"

speed only after it gained

some horizontal and vertical distance from the shooting position and the

place where the U-Boat was sighted by the enemy.

After the U-Boat has dived at required depth, put everything out of

action, listen carefully, in order to find out what the enemy is doing and act

accordingly.

181.  Always  go  down  dynamically
17
  to  a low depth!  Flooding is  a
mistake
18
. The U-Boat automatically becomes heavier with increasing depth
(leaking of the stern stuffing boxes and other openings, reduction of volume
of the hull of the U-Boat
19
) and it may well happen that it drops to a greater
depth than is intended. Consequently in diving to considerable depths, the
maximum motor power should be used, and it is even advisable to pump
out
20
 the boat (i.e, for type VII, ~1 ton!).
182. In steering the U-Boat downward to reach the required depth, the
trimming should at first be carried out by boat-hands
21
, if it transpires that
the diving planes are temporarily not sufficient; trimming with water is not a
necessity until the U-Boat has reached the required depth
22
. Care should be
exercised in trimming by boat-hands; "all-hands" maneuvers should not be
called for unnecessarily, but only in dangerous situations
23
.
183.  Do  not  go  down  to   an  unnecessary  depth  as   this  may  also   be
dangerous: the stern stuffing boxes and other hull closures leak badly, the
joints   are   subject   to   heavy   strain.  Always   choose   the   lesser   danger,  by
weighing   up   the   danger   from   depth   charges   against   the   danger   of   an
increased leakage of the water.
184. Concerning the measures to be taken against pursuit by listening
equipment and ASDIC, see Section IV.
185. Return to periscope depth only after careful investigation by means
of the listening equipment and after determining location of the enemy.
186. When the U-Boat is being brought up from a great depth, all the
hull closures should be gradually loosened, especially if any of them have
been tightened in order to adapt the boat to the depth conditions
24
.
187. Before surfacing after cruising at a great depth, the U-Boat should
first go at periscope depth, and after surfacing to be able to dive again at
once in case of an alarm.
188. Before surfacing, reduce as far as possible any over-pressure in the
U-Boat by means of the compressor
25
.
189.  After   surfacing,   before   final   blowing
26
,   the   surface   of   the   sea
should be carefully but quickly examined from the conning tower (see also
Section I, B, paragraph 29).
50

190. Free.

191. Free.

192. Free.

193. Free.

194. Free.

Section III.

The surface torpedo attack.

A. Fundamental rules for the night surface attack.

195. The surface torpedo attack by the U-Boat can only be carried out at

night. The object of the surface attack is the same as that of the underwater

attack and depends on the same ballistic factors; i.e., the torpedo attack at

short range which is carried out without warning and takes the enemy by

surprise (see Section II, A, paragraph 91).

196. Conditions affecting the night attack vary considerably. They

depend on the type of target, on the enemy escort, on the course and speed

of the enemy, on the conditions of visibility and light, on the state of the sea,

etc. The torpedo will therefore be discharged under many different angles

on the bow and from varying distances, depending on the various speeds

and changing course of the U-Boat, according to whether it is traveling on a

straight course or turning sharply at the same time evading the enemy cover.

Because of the low speed of the U-Boat, the commander will therefore, as a

general rule, be under the necessity of attacking under the angle on the bow

at the time of encountering the target.

197. There are, therefore, no hard and fast rules for the surface night

attack. It is only possible to establish the following fundamental rules as

generally correct:

a) Analogously to the torpedo-boat attack, the night surface

attack by the U-Boat should be launched, whenever

possible, under angle on the bow of 60° to 90°.

b) The own course during the surface attack should always be

run by compass, as the U-Boat commander is otherwise

liable to lose count of the position.

c) During the overhauling maneuver, the target bearing must

be constantly measured and the rate of change of target

bearing should be observed. The attack should not be given

up, even when the bearing only moves slowly. If, in spite of

every effort, the attack cannot be carried out in daylight, it must be

successfully made during the night. These values

are almost always more exact than the values estimated

during the attack. The values estimated by night are a

question of long experience and requires much practice.

d) At night, important miscalculations may easily occur in the

firing data. At night, the U-Boat should therefore go in as

close as possible, so that even serious miscalculations

cannot take effect to any great extent, on account of the

short run of the torpedo. Even if the U-Boat should be

sighted during the attack, it must no longer be possible for

the target to avoid the torpedo.

e) The minimum range for the night attack is also 300 m (see

Section II, A, paragraph 92).

f) At night, the discharging of the torpedo should not take

place prematurely from too small an angle on the bow.

Inexperienced torpedo shooters have the tendency to regard

the angle on the bow at night as grater than it really is. The

U-Boat commander should therefore keep his head and not

launch torpedoes prematurely.

g) A certain clue on the speed of the target is provided by the

extent of the turning maneuvers to keep him - dependent on

the distance – straight ahead.

h) Distances are already underestimated at night (see Section

II, A, paragraph 99). Do not let yourself be misled by the

increasing size of the shadow of the target and fire too early

at too long a range.

198. During the night surface attack, the U-Boat can be:

I. sighted,

II. located by listening equipment,

III. located by ASDIC.

I. Danger of being sighted.

199. As a matter of principle, the U-Boat commander should bear in

mind that the U-Boat is always more difficult to see at night than any

surface ship, unless the conditions of light are exceptionally unfavorable.

The reliance of the commander on the invisibility of his boat at night

increase with each new experience. Every contrary feeling must be

overcome by the consideration that the enemy whom the U-Boat is

attacking, being on the defensive, is in a weaker position, more especially as

his lookout, in consequence of long gruelling periods of duty, is in no

position to keep as good a watch as the U-Boat, which, at the moment, is

concentrating all its energy and attention on the development of the attack.

200. The difficulty of detecting the U-Boat at night on the surface due

to its long and low silhouette, since it disappears almost entirely in the

water, even including the conning tower. The conning tower can be most

easily detected by the enemy, when it rises above the dip of the horizon,

from the line of sight of the enemy. This is the danger zone for the

approaching U-Boat. Against the background of the sea alone, the conning

tower is very difficult to make out.

201. The conning tower of the U-Boat always appears as a darker

object, both in the dip of the horizon and against the background of the sea,

and even on the darkest night. In our latitudes, the most suitable color for

the conning tower, according to the experiences gained, is a light gray or a

dull white-gray; in the Atlantic, a dark blue-gray.

202. In view of the fact that paint, especially on the wet U-Boat, is

liable to reflect the light (shine), care must be taken not to show the enemy

the moon-lit side. If the circumstances make this unavoidable, the tapering

silhouette should be turned toward him as soon as possible.

203. Take care that the U-Boat does not appear in the track of the moon

on the water; i.e., in the line between the moon and the target.

204. Favorable conditions of attack, enabling the U-Boat to remain

unseen:

a) Attack the target when he can be seen against the light horizon, or

against the moon, and move toward him from the direction of the

dark horizon, or the dark portion of the sea. In this case, the U-Boat

itself is invisible even at the shortest distances from the target.

b) Go in with the sea, from windward, in order to reduce the bow

wave, which may well attract attention, especially if the sea is calm.

For the same reason it is advisable to proceed at low speed when

close to the enemy. This will also have the effect of reducing the

stern wave, which is apt to betray the U-Boat if the water is smooth.

In addition, the windward side has the advantage that it renders

observation more difficult for the enemy lookouts, more

particularly in a strong wind, or during rain.

c) During the attack it is always necessary and correct, to approach the

target, up to the point of discharging the torpedo or up to the point

of turning to fire the torpedo, in such a way as to show him the

narrow outline of the U-Boat. The bow and stern wave then merge

into one, and the form of the hull of the boat itself, which might

betray itself by contours of foam if it presented a larger surface to

the enemy, is then sure to be invisible. A favorable method of

attack is therefore to approach with the narrow angle on the

bow, and keep on turning, to show only the narrow outline

of the U-Boat, that is approaching by the "dog curve".

d) Caution should be observed during the transition from night to day,

on account of the rapid alteration of the range of visibility.

205. Free.

206. Free.

II. Danger of being located by listening equipment.

207. The sound of the U-Boat's engines is for practical purposes

inaudible on the surface, through the air, more especially in view of the

sounds proceeding from the enemy.

208. To what extent the other sounds made by the U-Boat when

cruising on the surface (noise of the screws, etc.) can be sound-

located by the enemy and distinguished as U-Boat noises from the sounds

made by the enemy himself, which increase in proportion to his speed and

the condition of the sea, depends on the circumstances dealt with in Section

I, B, II.

208. If the conditions for sound-locating are good, a U-Boat propelled

by diesel engines and traveling on the surface can, however, be heard much

more distinctly than a U-Boat with electric motors traveling underwater or

on the surface. If, therefore, enemy sound location is to be anticipated, and

especially if the speed of the enemy is slow and the sea calm, the attempt

must be made to go in for the attack on electric motors provided that the

position of the U-Boat in relation to the target will allow this, considering

the slow speed of the electric motors.

209. Free.

210. In no circumstances should the danger of being located by enemy

listening equipment during the night attack be overestimated, and the

opportunity of carrying out a fatal attack at short range be neglected on that

account (see Section II, A, paragraph 94).

211. Free.

212. Free.

213. Free.

III. Danger of being located by ASDIC.

214. It will only be in rare cases, when the sea is calm and the enemy

speed slow, that a U-Boat on the surface is located by ASDIC. The

conditions governing the hunting operations to be directed against a

surfaced U-Boat are usually less favorable than when the ASDIC is applied

to a U-Boat cruising underwater in a quiet area, on account of the higher

interference level on the surface (constant permeation of the surface of the

water with air by the movement of the sea and the vessel).

215. The danger from enemy detecting operations with ASDIC should

consequently be no more overestimated than the danger of being located by

means of the listening equipment and should on no account lead to the

abandonment of the attack (see Section II, A, Paragraph 94).

216. It must be assumed that some warships are provided with surface

detection equipment (Radar). The suspicion that this is so must not,

however, cause the commander to think that he has been located each time

the target or the enemy escorting vessels appear to execute a special

maneuver, and thereupon to give up his attack.

In almost all such cases, the movements of the enemy are evasive

movements which happen to be taking place at the time. It is not until it is

quite certain that the enemy movements mean that the U-Boat is being

pursued, that the latter should leave the scene of operations and submerge if

the enemy comes into sight. Further action according to paragraph 180.

Before submerging or before going deep suddenly change the course.

Remember that the first and most dangerous depth charges are dropped on

the spot where the U-Boat has dived and on the course which the enemy

supposes the U-Boat will follow in leaving the theater of operations.

217. Free.

218. Free.

B. Preparation for the surface night attack.

219. The general rules for the preparation for the underwater attack (see

Section II, B, paragraph 105) apply logically also to the night surface attack.

Special attention is called to the necessity of obtaining reliable firing data

even at night, and in all circumstances and by all possible means

(suppressing the changes of the target course and speed: see paragraph

105, e).

220. In sea areas where contact with the enemy may be expected at

night, at least one ready for action torpedo must be carried in the flooded

tube.

If the enemy is sighted suddenly, there may in certain circumstances not be

enough time to ready the tubes.

221. In war, the success or failure of night operations is more than ever

dependent on good eyesight and a good lookout. He who sees first always

has the advantage. Consequently, the place for the people who can see best

at night is the conning tower, more especially during the attack itself.

The lookout should be kept at night with binoculars only. In rain or

heavy seas, a man should be sent on to the conning tower for the special

purpose of holding dry glasses ready and wiping wet glasses.

222. When a target is sighted, first show the narrow side, keep the

speed, ascertain the change in bearing, and try then to reach a position ahead

of the beam, cruising at top speed on the confines of the enemy's range of

sight, in order to be able to carry out the attack. Do not give up the attempt

to bring the U-Boat forward to a position ahead of the beam, and thus to

make the attack, even when the excess of speed of the U-Boat appears only

slight. Changes of course on the part of the target may alter the chances of

success of the U-Boat at any moment.

223. The most favorable quarter (dark horizon, windward side, etc.)

should already be selected while the U-Boat is on the way to take up its

position for the attack. If the circumstances are such that the overhauling

process will probably last some time, it will be necessary, on moonlit nights,

to take into account the change of the lunar azimuth up to the time of the

attack.

If the conditions of light have changed, for any reason, during the

overtaking maneuver (parting of the cloud cover, etc.), it may be necessary

to maneuver round to the other side for the purpose of carrying out the

attack.

224. Free.

225. Free.

226. Free.

C. Carrying out the surface night attack.

227. After having reached the desired position ahead of the target's

beam, the attack commences. In this case, the most important rule to be

observed is: remain in the narrow position until the torpedo is discharged

– pursuit on the "dog's curve". Any widening of the outline of the U-Boat

may betray it.

228. When attacking, keep the U-Boat underway. Otherwise evasive

action on the surface or emergency diving during or after the attack, in face

of enemy escorting, forces, is not possible in time.

229. On meeting with enemy escorting ships, try to evade them, as far

as is possible, without submerging, in order to retain your mobility and be

able to take in the situation. On the surface, the U-Boat commander remains

master of the situation. If the U-Boat submerges, it becomes blind and

stationary, and must leave it to the enemy to bring about any change of the

position on the surface.

230. The advantage of the narrow outline while attacking is ensured by

the fire control system

231. On meeting an enemy convoy, advantage must be taken of this rare

opportunity, at night as well as in daytime, by utilizing to,the full

possibilities of the boat and the torpedoes. After the first target, a second

and a third target should be attacked at once. The confusion among the

enemy forces which usually occurs at night, after the launching of the first

torpedo, will make this easier.

232. As regards multiple shots and fan shooting, the rules laid down for

underwater firing of torpedoes (see Section II, E, paragraphs 171 to 174)

also apply to the surface use of torpedoes.

233. Free.

234. Free.

D. Proceeding after night surface attack.

235. After the night surface attack, the commander should endeavor to

stay on the surface, in order to observe the success of the attack, and, if

conditions are favorable, to organize a second and third attack. Do not go

deep down unless it is necessary; going down renders you blind and

helpless. On the surface, the commander continues to be able to take in the

situation, and retains his liberty of action. The U-Boat should, therefore,

only submerge when compelled to do so by direct pursuit.

236. After firing the torpedo, it will in most cases be right to turn at

once sharply toward the target's stern, in order as quickly as possible to get

out of the dangerous sector ahead of the target's beam, in which the danger

of being sighted and rammed is greatest.

237. If the U-Boat is able to remain on the surface after the attack, it

should make a short run outward, in order to be able to get in the next

torpedo launch as soon as possible.

238. If the U-Boat is forced to dive, on account of the development of

the pursuit, then it should first do so at top speed, and proceed in a direction

leading away from the scene of action and the course of the torpedo

. In

doing this, it is unnecessary to take into account any danger of sound

location. After a hit at night, there is such confusion on the surface that the

enemy anti-submarine detecting service will not be able, with any degree of

certainty, to sound-locate by means of the listening equipment or ASDIC

any U-Boat traveling below the surface.

239. The U-Boat should make off, underwater, at full speed on a

straight course, in order to take the shortest way out of the area covered by

the enemy defense. It will be able the sooner to surface again.

The direction of retreat should be an oblique forward course relation to

the course of the enemy, not a backward course, so that the U-Boat may

again run to windward of the enemy, even under water, while preparing to

carrying out the next attack.

240. How far the U-Boat should move away underwater after the dive

depends on the visibility. The enemy must still be in sight when the U-Boat

surfaces again; but the U-Boat itself must not be spotted on surfacing.

Generally speaking, a run of 2,000 to 3,000 m will suffice.

241. In surfacing, the U-Boat should observe the rules laid down for

that purpose: listening to the enemy, then quickly blowing, immediately

open the conning tower hatch, all-round view for the enemy and according

to the circumstances entirely blow the tanks.

If another attack is practicable, go forward at once and carry out the

attack.

242. For rules of action in case of underwater pursuit by the enemy, see

Section IV, paragraphs 246 to 269.

243. Free.

244. Free.

245. Free.

1 Such as salinity and temperature.

2 That is the usage of the Auswanderungsverfahren method.

3 Using the dazzle camouflage.

4 Germ. Feste Linie im Raum (stabilized azimuth line), that is, the

additional equipment of the Zeiss periscopes, which facilitated the

assessment of the target bearing change rate. The idea was to place in

the periscope view field the gyro-stabilized line, which would stay in

the place regardless the own boat course changes and regardless the

changes of the periscope bearing.

5 That is the usage of the Ausdampfverfahren method.

6 These are the approximate values calculated from the sines of the angle

on the bow. The calculated values are used to determine distance to the

target in the moment of the torpedo launch for angle on the bow equal

to 90° (Section D I 146 and further).

7 The usage of the 6x magnification requires introducing to the optical

system of the periscope additional lens. These additional lens decrease

the amount of the light, which is transmitted to the ocular, and as a

result the observed image is darker.

8 The torpedo fire control system allows for launching torpedoes with the

gyro angle in range from 0 to 90°, however, the greater gyro angle, the

greater value of the parallax correction has be taken into account during

calculations. The value of the parallax correction depends, among

others, on the distance to the target. That means, the more accurate

distance to target is, the more accurate is resulting parallax correction.

To minimize the influence of possibly wrong distance assessment, it

was recommended to launch torpedoes at small gyro angle values. See

paragraph 143.

9 The T.V.Re. S. 3 torpedo calculator is an electromechanical device. The

servos are used to automatically solve the torpedo triangle. In case of

the power supply failure – when the servos are not working – the

calculator can be operated manually. The operator – by means of the

handles – matches the pointers at the dials. When they are matched, the

torpedo triangle equations are solved.

10 For example: the angle on the bow is 37° port, target bearing is 291°,

own course is 140°. The target course is thus 293°, course perpendicular

(toward the port side of the target): 23°. Let us assume that the torpedo

deflection angle (calculated for the angle on the bow in the moment of

torpedo launch equal to 90°) is 56°. So the resulting attack course is 0°.

11 For example: the angle on the bow is 51° starboard, target bearing is

315°, own course is 307°. The target course is thus 31°, the course with

angle 60° to the target course (toward the starboard side of the target):

271°. Let us assume that the torpedo deflection angle (calculated for the

angle on the bow in the moment of torpedo launch equal to 60°) is 33°.

So the resulting attack course is 304°.

12 This is the average parallax correction for the gyro angle 45°: ~30 m

(Winkeleinsteuerungsversetzung for G7a and G7e torpedoes) + ~25 m

distance between the periscope and torpedo tubes.

13 Multiple discharges, in contrast to the salvo shot, mean launching

several torpedoes, of those each runs with different course, because

each was aimed to the different point. In case of the salvo shot, each

torpedo runs with different course, but all these courses were calculated

relative to the common aiming point.

14 “Listening speed” (Germ. Horchfahrt) is the maximum speed of the U-

Boat, by which the hydrophones can be used efficiently.

15 Possibly conducted by other U-Boats.

16 “Silent running” (Germ. Schleichfahrt) is the value of the U-Boat

speed, at which the noise generated by propelling machinery is the

lowest. During “silent running”, all unnecessary equipment (which

generates noise) is turned off (pumps, air-blowers, rotary converters).

17 Dynamically, that is, using the diving planes and thrust of the propellers

driven by electric motors.

18 Flooding of the regulation tanks increases the U-Boat weight (increases

its negative buoyancy) and accelerates diving (causes sinking).

19 Reduction of the hull volume (as the result of the increasing external

pressure) when the weight of the boat is constant causes the reduction

of water volume, which is displaced by the hull and, as a result,

reduction of the buoyancy (when the weight is constant, it leads to the

sinking of the boat).

20 Pumping out the water from the bilges or regulation tanks.

21 Diving planes could be ineffective due to low speed, too large

bow/stern trim or because the stern/bow is weighted to much (for

example due to flooding). Then - to change the trim of the boat – the

mass displacement inside the boat was changed by moving the crew

members.

22 The other way to change the trim of the boat was to move some

amounts of water between two trimming tanks, which were located at

the bow and stern.

23 Usually, the rapid changes of the trim were avoided, so the crew

members were moved within single the compartments. In emergency,

when the rapid trim change was required, the order “all-hands

forward/aft” (Germ. “Alle Mann voraus/Alle Mann achteraus”) was

issued, when the crew members were moved to the forward/aft

compartment.

24 At greater depths, the hatches, which are tight at smaller depth, start to

leak due to larger external water pressure. Thus they were tightened –

and in the greater extent than it would be possible at smaller depth,

because there were additional external force. After surfacing, so

tightened hatches could not be opened – so they had to be gradually

loosened while surfacing (according to the external pressure changes).

25 Over-pressure inside the U-Boat hull was created from the leaks of the

compressed air installations, the venting of the torpedo tubes during the

launches and venting the regulation, ballast and negative buoyancy

tanks. After surfacing, while opening the conning tower hatch, the great

over-pressure could throw the man out through the hatch. That's why

the over-pressure should be reduced by the running air-compressor.

26 The surfacing U-Boat does not blow all ballast tanks at once. Only few

ballast tanks are blown, sufficiently to surface the bridge over the water.

Then the bridge watch can take their station and scan the horizon

visually. If there was any danger, the boat could dive immediately. If it

was safe, all remaining ballast tanks were blown and the U-Boat got so-

called surfaced-condition.

27 During the attack (on the “dog curve”), the U-Boat's course is changing,

while the target bearing remains constant (and equal to 0). The angle on

the bow entered into calculator at the beginning of the attack is updated

continuously by torpedo calculator, which takes into account the

changes of own course.

28 Launched by other U-Boats.