S E C R E T

NAVY DEPARTMENT

OFFICE OF THE CHIEF OF NAVAL OPERATIONS

WASHINGTON

Final Report - G/Serial 27

REPORT ON THE

INTERROGATION OF SURVIVORS FROM U-664

SUNK 9 AUGUST 1943

S E C R E T

TABLE OF CONTENTS

				Page
CHAPTER	I.		INTRODUCTORY REMARKS	1
	II.		DETAILS OF U-664	3
	III.		TECHNICAL DETAILS AND PROCEDURE	19
	IV.		DESCRIPTION AND TECHNICAL USES OF NEW GERMAN TORPEDOES AND PISTOLS	26
	V.		GERMAN NAVAL RADIO INTELLIGENCE (B-DIENST)	59
	VI.		CREW OF U-664	64
	VII.		EARLY HISTORY OF U-664	69
	VIII.		FIRST PATROL OF U-664	72
	IX.		SECOND PATROL OF U-664	74
	X.		THIRD PATROL OF U-664	78
	XI.		FOURTH PATROL OF U-664	83
	XII.		FIFTH AND LAST PATROL OF U-664	88
	XIII.		SINKING OF U-664	96
	XIV.		TACTICS	101
	XV.		BASES	103
	XVI.		OTHER U-BOATS	106
	XVII.		SURFACE SHIPS	115
	XVIII.		GENERAL REMARKS ON U-BOATS	118
	XIX.		MORALE	122
ANNEX			CREW LIST OF U-664 AND U.S. EQUIVALENTS OF GERMAN NAVAL RANKS

CHAPTER I.  INTRODUCTION

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        The exceedingly low morale aboard U-664 no doubt facilitated the interrogation, and more than one prisoner was willing to cooperate fully with the interrogation officer.

- 2 -

CHAPTER II.  DETAILS OF U-664

TONNAGE.

        500 tons.

TYPE.

        VII C.

BUILDING YARD.

        Howaldtwerke, Hamburg.

YARD NUMBER.

        813.

COMMSSIONED.

        18 June 1942.

FLOTILLA.

        Ninth Flotilla at Brest.

FIELD POST NUMBER.

        05024.

PATRON CITY.

        Gaggenau.  (Baden.)

CALL LETTERS.

        XGU.

INSIGNIA.

        Sawfish Insignia of 9th Flotilla.

- 3 -

LENGTH OVER ALL.

        220 feet.

PRESSURE HULL, DIAMETER.

        15 feet.

PRESSURE HULL PLATING, THICKNESS.

        18 mm. in control room, tapering to 16 mm. in bow and stern.

SPACING BETWEEN PRESSURE HULL AND UPPER DECK.

        Normal.

DISPOSITION OF FRAMES.

Numbers	Location
0 to 16	Stern compartment
16 to 29	Diesel compartment
29 to 39	Galley and P.O.'s quarters
39 to 52-1/2	Control room
52-1/2 to 68	Officers' and C.P.O.'s quarters
68 to 82	Forward torpedo compartment

HATCHES.

        Total of 7, bow torpedo loading hatch, conning tower hatch, galley hatch, stern torpedo loading hatch, all of the foregoing hinged for opening and closing; one engine room access hatch and two battery access hatches, riveted.  The galley hatch was inaccessible after Platform II was added just prior to the last patrol.

BULKHEADS.

        One each fore and aft of control room.

- 4 -

GENERAL CONSTRUCTION.

        Completely welded, including attachment of flanges to pressure hull and bulkheads.

DRAFT, FULLY LOADED.

        15 feet.

PERISCOPES.

        One observation periscope, actuated by hydraulic cylinders and wire cables.

        One attack periscope, actuated by piston, fitted with riding seat, in conning tower.

"PAPENBERG" DEPTH GAUGE.

        Fitted.  This depth gauge is located in the control room.  It was described as about 150 cm. long and 5 cm. wide; the silhouette of periscope and bridge was painted on it.  Graduated to 20 m., it is used for exact determination of periscope depth preceding and during an underwater approach and attack.

CRASH DIVING TIME.

        Before platform I was widened and platform II added, i.e. prior to last patrol, U-664 dived to periscope depth, 13 m., in 18 seconds.  After changing the superstructure the diving time was increased to 28 seconds.

MAXIMUM DEPTH ATTAINED BY U-664.

        On several occasions U-664 dived to 250 m., without discomfort to the crew.  It was stated that the yard guarantees a boat up to 150 depth.

- 5 -

BRIDGE ARMOR.

        16 mm. armor plate fitted around forward bridge fairing; armored doors, 12 mm. thickness, fitted between bridge and platform I.

GUN PLATFORMS.

        Two.  Platform I, widened prior to last patrol; platform II, added at the same time.

GUNS.

        No forward gun.  88 mm. gun removed after fourth patrol.

        Two 20 mm. cannons on platform I; quadruple mounted 20 mm. cannons on platform II.

        Two type 15 demountable machine guns on bridge.

QUADRUPLE MOUNTED 20 mm. CANNONS.

        Four barrels, two over two.  Vertical splinter shields on both sides of mount; estimated thickness 8 mm.  (See photograph.)  Seat for gunner turns with mount; it does not raise or lower with it, however.  Mount is raised and turned by hand rods.  Cable and spring arrangement acts as counter-weight.

        Aiming by ring sight.  Outer rings stated for target speed of 360 km.; second ring 180 km.; inner ring for diving planes or for target requiring no lead.

        No automatic stop; railing, both forward and aft, acts as such.

        Vertical elevation 90⁰; traverse angle 360⁰; depression angle believed 10⁰.

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        All four barrels set parallel, arranged as follows:

                                3        1

                                2        4

        Firing order 1, 2, 3, 4.

        Firing speed per minute:  (a)  theoretical - 200 rounds per barrel

                                              (b)  actual - 80 rounds per barrel

TYPE 15 MACHINE GUN.

        Estimated firing speed two-drum-shaped magazines per minute.  Each magazine contains 75 rounds; on U-664 each second round was a tracer.

20 MM.  AMMUNITION.

        20,000 round aboard U-664; packed in metal containers each containing 100 rounds.  Containers were distributed all over the boat.

        U-664 had the following types of ammunition on board:

                Incendiary - H/E, with tracer; stated to be flat nosed, yellow with red band.  Explodes on contact or may be fuzed.  (On U-664's fourth patrol this was the only type ammunition carried.)

                Incendiary - H/E, without tracer.  Yellow, no red band.

                A/P - H/E, no tracer.  Black

                May also have carried A/P with phosphorus charge, no tracer.  Blue.

        Extreme and self-destroying range stated to be 2,000 m.  Effective range 2100 - 2200 meters.

MAGAZINES.

        168 magazines carried.  Empty magazines were filled in the ammunition chamber by a loading machine.  Filled magazines could be stowed as follows:  80, four rows of 20, in the control room; four in each of the

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five pressure-proof ready-ammunition lockers below platforms I and II; 10 aft of periscope in the conning tower.

        Magazines not marked as to type or order of ammunition contained therein.

PRESSURE PROOF READY AMMUNITION LOCKERS.

        Five lockers installed before leaving on last patrol.  One located between bridge and Platform I, just aft of attack periscope; four located between platform I and II; two over two.

TORPEDO TUBES.

        Five; four forward, one aft.  All tubes fitted with F.A.T. gear since February 1943.

TORPEDOS CARRIED.

        First patrol      - 6 air, 8 electric.

 

        Second patrol - 4 air, 6 electric, 4 electric with combination magnetic-impact pistols.

        Third patrol     - 2 air, 8 electric, 4 F.A.T.

        Fourth patrol   - 8 electric, 4 F.A.T.

        Fifth patrol      - 4 electric, 5 F.A.T., 3 acoustic.

UPPER DECK CONTAINERS.

        Two carried on first three patrols; two air torpedoes carried therein on those patrols.

TORPEDO STOWAGE ON LAST PATROL.

        Four in forward tubes, 1 an acoustic torpedo; 2 on forward floor

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plates; 4 in forward bilges; 1 (acoustic) in stern tube; 1 (acoustic) in stern bilge.

EXPELLING PRESSURE.

        Stated to be 12 atm. on surface shots; 16 atm. on submerged shots.

S.B.T.

        Fitted.  (See also Chapter III.)

DEPTH CHARGE PLOTTER (D.P.C.).

        Not fitted.

ENGINES.

        Two G.W. 6 cylinder, single acting, four cycle Diesels, 1400 H.P. each with supercharging.  860 H.P. without supercharging at 350 R.P.M.

ENGINE SPEEDS.

Telegraph Speeds	R.P.M.	Speed
K.F. (Dead Slow)	185	7.2 knots
L.F. (Slow)	245	9.7    "
H.F. (Half Speed)	285	12.7  "
2x H.F. (3/4 Speed)	385	14     "
G.F. (3/4 Speed)	450	16     "
2x G.F. (Full Speed)	475	16.8  "
A.K. (Emergency Speed)	485-490	17.5  "
3x A.K. (Emergency Speed)	495	17.8  "

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        Speeds of 2x H.F., and higher were always attained with supercharging.

        At 3/4 speed (2x H.F.) with battery charging, engines turned at 350 R.P.M.  Half speed on both engines was considered cruising speed.  In operational area, one engine was run at slow speed, turning over 200 R.P.M. at a rate of travel of 4 knots.  Diesel-Electric propulsion was used only once during the trials of U-664.  An engine room petty officer stated that very few U-boats used Diesel-Electric propulsion.

SUPERCHARGERS.

        2 "Kapselgeblase".  Positive displacement (Rootes) type, fitted with mechanical friction clutch manipulated from engine control stands.  Although drive has intermediate gearing and cushioning springs, frequent replacement is necessary.

CLUTCHES.

        Disc friction type, pneumatically actuated, and with emergency hand wheel actuation.

FUEL OIL CAPACITY.

        About 140 cubic meters (120 tons).  The prisoner stated that the increased capacity was obtained by filling 3 torpedo compensating tanks is pumped into the regular tanks.

FUEL OIL CONSUMPTION.

        During tactical exercises on a 24 hour run, 22 of which were at 3/4 speed and 2 at half speed, 12 cubic meters of oil were used, or about 0.5 cubic meters average per hour, which figure normally varied

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from 0.5 to 0.55 on U-664.  On the fourth patrol U-664 ran for six weeks without being supplied.  Fuel oil consumption when running on one engine varied from 1.6 to 2.6 cubic meters per day on this patrol.

MOTORS/GENERATORS.

        Two A.E.G. double units, each normally 365 H.P., but 420 to 470 H.P. when crowded as motors.  About 50 - 100% greater generating capacity.

MOTOR SPEEDS (Submerged).

Telegraph Speeds	R.P.M.	Speed
K.F. (Dead Slow)	58	1.2 knots
L.F. (Slow) *	90	1.5    "
L.F. (Slow)	110	2.8    "
H.F. (Half Speed)	160	3.6    "
2x H.F. (3/4 Speed)	210	4.5    "
G.F. (Full Speed)	260	5.1    "
A.K. (Emergency Speed)	300	6.5    "

Note:  *  L.F. Speed with 1 motor only; all other speeds with both motors.  (O.N.I. Note:  Attention is called to the apparent discrepancy of R.P.M. and actual speed for full speed and emergency speed.)

        Survivors estimated emergency speed at about 7.1 knots before addition of platform II and widening of platform I.

BATTERIES.

        Two banks of 62 cells each, lead-acid type.  The batteries were known as model 33 MAL 800 W.  Capacity of U-664's batteries was 9,600 ampere hours; normally this should be 10,000.  At full speed the batteries were exhausted in 4 to 5 hours.  Below half speed, batteries were connected

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in parallel; at and above, in series.  At dead slow, the armatures of the motors-generators were connected in series; at 3/4 speed, in parallel.  (Connections for other speeds were not stated.)  Maximum non-spilling angle 65⁰.

ROTARY CONVERTER.

        One 0.3 K.V.A. on top of Port Motor/Generator for radio.

        One compound wound for Gyro; 110 volts, 55 or 333 cycles.

        One 1 K.V.A.

        One 1.5 K.V. for new radio apparatus, also for patent log, salinity determinator at fresh water still, multiple hydrophone, radio transmitters and receivers.

        One 6 K.V.A. for main transmitter and for all radio purposes.

        One for fire control apparatus.

        One for Echo sounder.

        One CONZ (Siemens) for radio, probably high frequency.

        No rotary converter was used for supplying constant voltage lighting current.  Battery current was fed through an automatic voltage regulator located on the auxiliary switchboard.  Hand controls also were fitted.  The automatic regulator consisted of a small motor turning a centrifugal governor which engaged a toothed rack which slid a contact back and forth on a resistance.

COMPRESSORS.

        One electric 4-stage compressor.  Capacity 6 liters per minute at 250 atmospheres.  One Junkers crankless Diesel compressor, 4-stage capacity 8 to 11 liters per minute at 250 atmospheres.  The Junkers compressor

- 12 -

was mounted on a base and also had emergency suspension by wire cables from the overhead after the second patrol.  One cable had been left off due to its interference with the operation of the S.B.T. apparatus.  At the sinking, the base was knocked out; the emergency suspension proved unsatisfactory due to the one cable missing.  Both compressors were regularly exchanged after each patrol for others which had been thoroughly overhauled.

COMPRESSED AIR SUPPLY.

        Consisted of 6 groups of 2 bottles each, capacity per bottle 360 liters; total capacity 3,900 liter.  Pressure 250 atmospheres (3675 P.S.I.).  Starting air at 35 atmospheres carried in two bottles, one behind each Diesel, they were filled from Group 1.  H.P. air bottles located aft in upper deck.

OXYGEN SUPPLY.

        On last cruise six bottles of liquid oxygen replaced compressed gaseous oxygen in the oxygen system.  An ordinary pressure reduction valve was used and oxygen was added to air circulation system in customary manner.

PUMPS.

        One main ballast, double impeller centrifugal; 250 liters per minute, impellers in series; at depth of 60 to 80 meters, impellers are used in series; capacity is reduced an average of 10 liters per minute for every 10 meters greater depth.  380 liters per minute,impellers in parallel.  One auxiliary ballast, reciprocating.  Capacity, 150 liters per minute, maximum depth 30 to 40 meters.

- 13 -

        The greatest depth at which ballast could be pumped outboard with both pumps in series was 240 to 250 meters.

        One auxiliary engine cooling water pump could be used to pump out forward Diesel bilge.

        Note:  bilges could also be pumped into compensating tank and blown.

SPARE PARTS.

        7 or 8 Bosch injector needle valves and springs.

        A number of intake and exhaust valves and valve springs for Diesels.

        1 Cylinder head for Diesel.

        1 main bearing for Diesel.

        No spare piston rings for Diesels or compressors were carried.

        Prisoners stated that amount of spare parts carried was small due to scarcity.

GERMAN ASDIC.

        Not fitted.

RADAR.

        Not fitted.  It was said to be installed after the completion of the fifth patrol; an extensible radar aerial was to take the place of the extensible rod aerial.

R.D.B.

        Balloons carried in three sheet metal containers stowed in the forward torpedo compartment.  The containers were marked "A.E.G."  Four

- 14 -

hydrogen bottles installed prior to last patrol just abaft the 20 mm. quadruple mounted cannons on platform II.  Balloons not used, except one which was fired at for target practice.

G.S.R.

        Metox R 600 fitted; fixed round net-type dipole aerial installed prior to last patrol (see drawing).  Metox fitted with "magic eye" since fourth patrol.  A visual indicator (cathode-ray tube) was connected with the Metox prior to the last patrol; it was set atop the Metox.  Two spare cross-type aerials were carried.

D/F GEAR

        Standard D/F apparatus manufactured by Lorenz; range from approximately 12 kc. to 1500 kc.

        Special Lorenz D/F apparatus fitted prior to last patrol; range about 500 kc. to 5000 kc.  For use of radio intelligence operatives aboard after interception of convoy traffic.  (See drawing attached.)

TRANSMITTERS.

        H/F Telefunken transmitter; 200 w.; - 8 or 10 stage.

        L/F - M/F Telefunken transmitter; 150 w.; 500-100 m.; 2 stages.

        Emergency Telefunken transmitter; 40 w.; 20-60 m.

RECEIVERS.

        All wave receiver.

        H/F receiver; 20-80 m.

        Standard broadcast receiver.

        All-wave intercept receiver; used only by radio intelligence personnel (see drawing attached).

        4 - 8 m. receiver, manufactured by S.A.D.I.R. Located in listening

- 15 -

room atop the emergency Telefunken transmitter.  Its aerial was a rod-type radiating aerial which was demountable and which was located on the port side of the forward conning tower fairing.

        S.A.D.I.R. was installed just before U-664 left on her last patrol.  It is believed to have been an experimental set designed to intercept airplane carrier's homing beacons.  (For further details, see chapter III.)

PERISCOPE AERIAL.

        Fitted.  Consisted of cable from stern to periscope; cable taut when periscope fully extended.

EXTENSIBLE ROD AERIAL.

        Fitted on port side of conning tower fairing.

UNDERWATER TELEGRAPHY.

        Fitted.  Not used except on trials and within 100 fathom line along French coast.

R/T TRANSMITTER.

        Dismounted after completion of trials in the Baltic.  It was a "Tornistergerät" and was located above the master gyro.

WATCHES OF RADIO PERSONNEL.

        0800 to 1200; 1200 to 1600; 1600 to 2000; 2000 to 0200; 0200 to 0800.

HYDROPHONES.

        Multiple hydrophones (G.H.G.) fitted.

- 16 -

NAVIGATIONAL AIDS.

        One master gyro (Anschütz); three repeaters, two in control room and one in pressure-tight case on port side of bridge.

        Magnetic compass housed in bulge at base of conning tower; projected from there into control room.

        Push button rudder control (B.B.C.); one in control room, one in conning tower with cable for use on bridge.

        Rudder motor hand control in stern compartment.

        Two push button hydroplane control boxes in control room, one each for stern and bow planes.

ELEKTROLOT.

        Fitted.

ECHOSOUNDER.

        Fitted (Atlas).

AIR PURIFICATION.

        200 potash cartridges carried.

LIFE RAFTS.

        About 20 to 30 one-man rubber rafts carried; stowed under bunks.

        One "Universal" rubber raft, fully equipped; holds about 25 men.  Stowed under forward deck grating.

POLARIZED GLASSES.

        Provided for bridge watch, enabling them to look directly into the sun.

- 17 -

RED GLASSES.

        The C/O and his first watch officer each had a pair of red goggles which they used in the control room prior to standing night watch in the conning tower or on the bridge.

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CHAPTER III.  TECHNICAL DETAILS AND PROCEDURES.

A/C ALARM.

        When alarm is sounded, a petty officer and a seaman man the 20 mm. quadruple mount.  The petty officer is gunner and trainer (Scitenrichter); the seaman acts as pointer (Höenrichter).  Another enlisted man opens one of the ready-ammunition lockers, while another member of the crew mans one of the single 20 mm. cannons.  Four additional men then supplement the provisional gun crew:  one operates the second 20 mm. cannon while the other three pass ammunition to the 20 mm. quadruple mount and the two singles respectively.

        Five men, at various stations pass ammunition from the control room through the conning tower on to the bridge.

        The "order transmitter" (Befehlsübermittler) takes his post in the conning tower.

BARRAGE A/A FIRE.

        Barrage fire was never used on U-664.

AIMING AND FIRING AT ATTACKING A/C.

        Gunners on U-664 were taught to aim at the motors of twin engined airplanes; in practice, however, the gunners aimed at the nose of the plane.  When attacked by fighter planes, the motor or the cockpit were aimed at.

        Prisoners from U-664 stated that they started firing as soon as the planes began its dive; usually, the estimated distance was 1700 - 1800 m.

- 19 -

        A gunner claimed that he found it easier to aim at low-flying airplanes rather than at planes flying at medium or high altitudes.  A diving airplane is considered an ideal target as it must remain on a steady course.

TRAINING OF A/A CREWS.

        Although quite well trained initially, gunners on U-boats cannot because of their other duties on board, attain the proficiency, through frequent practice, of their comrades on land.

LOADING OF S.B.T.  (See drawing attached.)

        Six containers with inserts are in a pack held together by two crossed paper tapes 2 cm. wide.  The entire pack of six is loaded and ejected.  After ejection springs shove inserts out of containers.

SERVICING OF S.B.T.

        While under way, both doors are locked, tube is drained and vent open.

        To operate S.B.T.:  Open drain and inner door which swings on a hinge.  Inject S.B.T. containers.  Shut inner door, leave drain open, open flooding lines; then close drain and vent.  Open outer door and eject containers by shoving plunger rod outwards.  After ejection, pull plunger rod back and close outer door.  Close flooding lines and open drain and vent, then open inner door.  Now ready for re-loading.

NOTES ON S.B.T. EJECTOR.

        The flooding apparatus is electrically welded to the pressure hull.  The inner door is opened sideways to the left.  Closure is like

- 20 -

that of the inner door of a torpedo tube.  The closure ring is controlled by the handle and is opened by a 90⁰ turn.

        The ring stays on the tube and the inner door is opened.  The outer door is opened by means of a rod and hand wheel.  Ten to fifteen turns of the hand wheel open the outer door upwards and to the left.  The outer door is about 10 cm. inboard of the after upper deck (fairing).  The flooding, drain, and vent lines each have 2 valves.  Drain and vent lines empty into the bilge through a funnel.

EVASIVE TACTICS AGAINST DEPTH CHARGE ATTACKS.

        U-664 consistently dived to 180 - 200 meters when being attacked with depth charges by surface vessels; it was claimed that in all such attacks detonations were above them.

        When depth charges were to be expected from aircraft, U-664 submerged to 70 - 120 meters; again detonation were in all cases above the U-boat.

        One prisoner stated that in March 1943, U-664 was advised that in future deeper depth charge settings might be expected; it was also rumored that depth charges acoustically detonated might be used.

ENGINE TROUBLE.

        In addition to routine maintenance and repair items, U-664 experienced difficulty only with the closure of needle valves and seats of the Bosch injector pumps.  Replacements were difficult to obtain, necessitating re-seating, following which, wear was excessive.  The prisoner stated that Bosch was using a poor grade of steel in those parts, due to scarcity of ferro-alloys.

- 21 -

MOTOR, GENERATOR TROUBLE.

        On first cruise four pole connecting bands burned out on account of water striking them either through ventilator or bilge drain.  Trouble was experienced with forward bearing on port Motor/Generator always running hot.  Additional cooling was effected with a stream of water from a hose.  At slower speeds Diesel cooling water was circulated through the cooling coils in the oil reservoir; at 3/4 speed and above, water was circulated through the coils by the auxiliary cooling pump.

TROUBLE WITH BATTERIES.

        On order to cool cells at a rapid rate of charging, battery tanks were flooded to 2/3 and 3/4 the height of cells.  At monthly overcharging of batteries, normal parallel voltage of 110 was run up to 169.  U-664 ran submerged for approximately 10 hours in Bay of Biscay on 3rd, 4th and 5th patrols, surfaced, and recharged batteries at 3/4 speed in about one hour, to the detriment of the batteries.

        Following fourth patrol three cells were pulled from each battery;  corrosion in after battery tank was welded and both tanks painted.

R.D.B.

        The balloons carried on U-664 were red and had had a diameter of about 25 cm.

        Only one member of the crew had seen a complete R.D.B. set, at Brest July 1943, and described it as follows:

        The balloon is attached to its float by a "string", length unknown.  At some point below the balloon two strings lead off; they are

- 22 -

about 8 to 9 meters long each.  To each of these, three strips, 6 - 7 cm. wide and 2 meters long, are fastened.

        The float was described as being made of thin sheet steel, having a flat top and a rounded bottom.  It was stated to have contained a white papery mass similar to blotting paper.

        On U-664 the balloons were in charge of the communications officer (second watch officer).

G.S.R.

        The Metox carried aboard U-664 was non directional.

        On U-664, the only crew members standing watches on the G.S.R. outside of the radio men, were torpedo men.  One of these stated that the "magic eye", which was added to the Metox set after the third patrol, would give indications of radar inaudible on headphones due to the weakness of the signal received.

G.S.R. AERIAL LEAD-IN.  (See drawing attached.)

        According to prisoners, the cable leading from the G.S.R. aerial into the listening room, through the pressure hull, is a weak spot.  When U-664 was attacked 9 August 1943, a leak developed immediately through the lead-in.  To combat the weakness, a special cutting mechanism was built into the ceiling of the listening room.  It permits the cutting of the cable; when the key is turned further, it also produces a water-tight fitting.  A special key is necessary to operate the mechanism.  When water leaked through this gland at the time of the sinking, the cutting of the cable did not however stop the flow of water; possibly the mechanism was not turned far enough.

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SADIR.

        It was established that this precision receiver was installed primarily to take bearings on homing beacons sent out by airplane carriers.

        The apparatus was brought on board U-664 shortly before her departure on the last patrol, and its installation was surrounded by considerable secrecy.  About the only people on board who knew about the purpose of the SADIR set were the commander, the communications officer and a radio electrician; the latter had assisted the communications officer in transporting the set from Berlin to the base.

        Even one of the other radiomen did not know the purpose of the set, claiming, as did most other ratings, that the SADIR set was an extension of the G.S.R. on the higher frequencies, designed to intercept what was called "inaudible search rays".

        The SADIR's aerial was a rod-type radiating aerial, demountable, located on the forward part of the conning tower fairing, port side.  It was to be demounted prior to each dive; in case this was impossible six spares were carried aboard to replace the aerial which would have been spoiled by submergence.

        The SADIR set was manned constantly during the first few days of the last patrol whenever the U-boat was surfaced; later the watch on the set was reduced, but toward the beginning of the third week under way SADIR was again used extensively.  As far as could be learned nothing whatever was heard on the apparatus although the operators had been told that the might expect continuous or intermittent tones similar to those heard on the G.S.R. set.

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        (Sketches of the SADIR set and its aerial are attached; further information on other SADIR sets, such as used by land stations, will be found in chapter V.)

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CHAPTER IV.  DESCRIPTION AND TACTICAL USES OF

                                                    NEW GERMAN TORPEDOES AND PISTOLS

DESIGNATION OF GERMAN TORPEDOES AND PISTOLS.

I.  TORPEDOES.

German Designation	Remarks
T-I or G7a	Air-driven; impact only
T-II or G7e	Electric-driven; impact only
T-III	Usual T-II; combination impact and magnetic firing
T-IV	Acoustic; electric-driven impact (inertia) only
T-V	Believed to be new type acoustic; electric-driven; speed 25 knots constant.

II.  PISTOLS.

Pi 1	No longer in use; old type; impact only short whiskers
Pi 2 or Pi G7h ("Pihans")	Impact only; long whiskers
Pi 3	Used with T-III; longer pistol; 3 long whiskers; combination impact and magnetic firing
Pi 4	Used only with T-IV; impact (inertia) only.

ACOUSTIC TORPEDO (T-IV)

I.  NAME.

        T-IV (torpedo the result of three year's research.)

II.  PROPULSION.

        Electric.

III.  MEASUREMENTS.

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        Entire torpedo slightly longer than ordinary type; extra length about six inches due to hard rubber-like nose in front of warhead; diameter twenty-one inches.

IV.  PROPELLERS.

        Two six-bladed propellers.  Propeller shaft tunnel continuously immersed in oil to reduce operating noise; oiling must be done every two days.

V.  SPEED.

        Twenty knots.  Constant.

VI.  DEPTH SETTING.

        One to twelve meters.  Air-controlled - - not acoustically.

VII.  PISTOL.

        Impact; inertia type; no whiskers.  According to P/W, pistol is entirely mechanical; containers two firing pins, a suspended ring, and a hook, when ring strikes anywhere, the two firing pins are struck downward by a spring which is always under tension; hook slips away and pistol sets off main charge.  Located in top center of warhead - - not in nose of warhead.  Brass composition.  Four bladed impeller attached to pistol.  Length of pistol, between eight and ten inches; diameter, between four and six inches.  Known as Pi 4; also known as "Erschutterungspistole" (shock-pistol).  Arming distance between two hundred and two hundred and fifty meters; depth does not influence arming distance or time.  Not magnetically fused.  Contains no anti-countermining device.  Is inserted into warhead from above and is fastened by three screws.  Impeller will not turn if torpedo is traveling less than seventeen knots (acts as safety device in event of a hot-runner.

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VIII.  WARHEAD.

        Same length and diameter as other warheads.  Charge consists of about six hundred and sixty pounds gun-cotton.  Total weight of warhead about the same as for other warheads.

IV.  DETONATION.

        Torpedo can be detonated by a jar or bump received on any part of the torpedo.  Can be detonated (against target) even by grazing.

X.  TEMPERATIRE LIMITATIONS.

        None.

XI.  SELF-DESTROYING DEVICE.

        None.

XII.  FIRING.

        Ejected from tube as are other torpedoes.  Does not leave tube under own power.  Piston used for submerged shots; only air (not piston) used for surface shots.  Bubble eliminator used for surface shots.

XIII.  RANGE.

        About 7200 meters.

XIV.  ACOUSTIC GEAR.

        Consists of two transformers, immersed in oil-like fluid, located in nose-cap forward of warhead.  Pick up propeller noises about one hundred meters from any type of target.  Pitch or tone of target's propeller vibrations has no effect because acoustic gear reacts to any pitch or tone of propeller noises.  Vibrations received one hundred and eighty degrees around nose-cap.  Distance from target when acoustic gear picks up vibrations depends on speed of target (but distance is between 100 and 200 meters from target).

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XV.  NOSE-CAP.

        Hard rubber-like substance; not fragile; red-brown color.  Estimated thickness about .23 (point two three) inches.  Rounded point nose-tip.  Screwed on with greased screws; no oil or grease must remain on cap.  Distance between tip of nose-cap and first bulkhead (which separates transformers from amplifier) about six inches.  When torpedo being loaded on U-boat, nose-cap has cover (for protection or camouflage) which is removed just before torpedo loaded into tube.  Nose-cap sealed off from rest of torpedo by bulkhead.  Cover name of nose-cap and transformers:  "Storch" (stork).

        The protective covering put over the nose-cap remains in place until the torpedo is put into the tube.  The point of the nose-cap is slightly rounded.  From there an even curve, not a cone.  This torpedo is more pointed than ordinary torpedoes.  The curve of the nose is carried back to the after end of the three inch bulkhead.  Rubber stops at front of bulkhead.

XVI.  FLUID.

        In nose-cap, in which transformers immersed.  Oil-like; reddish color; more dark than light.

        No reserve liquid for the cap was carried on board.  If ever leakage from the cap was discovered the torpedo would have to be returned unused.  The liquid in the nose-cap is transparent; it is clear, not cloudy.

XVII.  TRANSFORMERS.

        Two.  One to port; one to starboard.  Located on diameter line of nose-cap.  Flat shaped.  No partition between transformers.  Both

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immersed in oil-like fluid.  Back of each fastened to partition (i.e., bulkhead separating transformers from amplifier).  Distance between (each) transformer and bulkhead (to which fastened by means of a bolt) about .2 (point two) inches; this entire space taken up by a layer of rubber.  Distance between each transformer, between four and six inches.  Distance between (each) transformer and each side of nose-cap, about four inches.  Distance between (each) transformer and front of nose-cap, about four inches.  Each transformer has its own amplifier.  Term "transformer" ("Transformator") definitely used when P/W had instruction.  Acoustic gear hears only forward and sides (one hundred and eighty degrees); does not hear backward.  (In order to hear vibrations from rear, torpedo must circle and then pick up vibrations forward of it.)

        During instruction in Gotenhafen, PW saw the transformers within a glass cap.  This was a model for instruction purposes.  PW did NOT see the transformers in the torpedoes taken on board U-664.

XVIII.  TRANSFORMER CORE.

        Length, about four inches; width, about three inches; thickness, about one inch.  Not connected to any membrane.  Wire-wound sides face side of nose-cap; does not face nose.  Lies in same direction as does each transformer.  Fixed in transformer; not moveable.  Steel-like appearance; does not rust.  Consists of layers of several plates on both sides and ends;  plates not segmented.  Plates not continuous all way round.  Laminated to prevent eddy currents.  Not believed by P/W to be interchangeable.  Number and thickness of laminations not known by P/W.  Windings on both side of both transformers are very close together - - so close that prisoner could see no space between the winds.  Distance from end of core (on which winds are) to beginning of 1st wind is about one-half inch; same distance separates last wind from end of core.  (Therefore, the winds take up about three inches of the four-inch side.)

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XIX.  BATTERY.

        One only.  For propulsion only.  Fifty-five to fifty-seven volts.  Length, about four feet; width, about eighteen inches; height, about fourteen inches; weight, about 600 pounds.  Twenty cells; zinc plates.  Direct current.  Vented daily; charges every four to five days; heated daily in cold weather (particularly North Atlantic).  Smoking prohibited when ventilating takes place; some concern  felt about spark from motor igniting battery gas which has escaped into after body.  Three access-holes on top in battery chamber; exhaust valve on side.

        P/W thinks that there is sulfuric acid in the battery of the torpedo.  He really knows nothing about the battery.

  

        Direct current.  Carries six magnetic poles.  Eighty-eight horsepower.  Tested for one hundred and twenty-five amps.  Fifty-five volts.  Prisoner knows of no difference between this motor and that used in ordinary electric torpedo.

XXI.  GENERATOR.

        Located motor chamber; forward of and coupled to propulsion motor.  Produces direct current and alternating current.  Three circuits come off generator:  one to the transformers; one to gear actuating rudder throw.  Low tension (three to four volts) when current from generator reaches transformers.  (Based on P/W's remarks, the following operations are thought to be likely:  Primary of transformer is fed through (some kind of) a resistance from generator; vibrations of oil-like fluid cause an induced current to flow in the secondary circuit of transformer which, when amplified, operates relay controlling rudders.)

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        The generator is in three parts, 1 for transformer, 1 for amplifier, 1 for relays.  Generator is for purpose of supplying acoustic gear only.  Ordinary Etos have no generator.

XXII.  VOLTAGE (from generator).

        Three to four volts to rudder-throw gear.

XXIII.  GYRO.

        Operated by three air flasks located in tailpiece.  Once the acoustic gear has taken over, the gyro is no longer in control.  Gyro in control only during straight runs:  gyro is not in control as long as vibrations are heard, not in control while torpedo is circling.

XXIV.  AMPLIFIER.

        Fastened to bulkhead (back to back only) which separates amplifier from transformers.  Made of light metal; light gray color.  Measurements (in inches):  Fourteen by fourteen by sixteen.  Has removable cover (on top).  Prisoner saw, in box, tubes, resisters, anodes, and coils.  Layer of rubber (thickness not known) between amplifier and bulkhead.  Cover-name is "Ente" (duck).

        Source of PW's previous statement about anodes being in amplifier:  he was told this.

XXV.  "AMSEL" (or G-switch).

        Cover-name for gear determining whether torpedo when acoustic contact lost either to circle around same track until it sinks or to complete its initial turn, return to forward straight course and eventually sink.  "Amsel", also known as "G-Schalter" - - "Geschwindigkeitsschalter" (G-switch - - speed switch). is located between motor and gyro.  A setting

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spindle, which is set from the outside of the torpedo, is manipulated in the tube by means of the usual range-setting gear.  "Amsel" operative only when no more propeller vibrations from target are heard.  (Note:  If additional vibrations are picked up - - either from the original target or from any other target - - while the torpedo is making a turn, or while the torpedo is circling, or while the torpedo is on a straight run (after, of course, describing one circle) - - then the torpedo will deviate from its course and will describe turns or (if again losing contact) circles or a straight run.  The setting gear, located above the "Amsel" is not entirely the same type used in other torpedoes; the setting key, however, is the same.  Setting gear described a follows:

                                                         

Setting on tube are same, except that L/O not found.
WS:	"Weitschuss" (distant shot); used to cause torpedo to make one circle and then continue on forward straight run.
NS:	"Nahschuss" (near shot); used to cause torpedo to make circles along same track.  Said to be good setting when torpedo used against a convoy.
L/O:	Meaning not known; thought by P/W to signify "Laden" (Charge - - i.e., battery).  Torpedo can be fired when L/O setting used; in this event, torpedo operates as any ordinary electric-driven torpedo; acoustic gear not in operation at any time if torpedo fired on L/O setting.  L/O setting has not either anything to do with any safety element or with the changing of the torpedo into a homer.
SS:	"Schnellschuss" (fast shot); forbidden to use SS setting.  P/W believes SS setting may cause short circuit; does not know whether SS setting is part of a booby trap.

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        P/W believes terms WS, SS, etc. are "blinds".

        When torpedo being taken on board U-boat, setting in on L/O; when torpedo about to be loaded into tube, setting is changed either to WS or NS.  See XXXVI.  If WS or NS used, setting can be changed from either one to the other while torp is in tube.  If WS or NS is used, setting to L/O cannot be made while torpedo is in tube; torpedo must be removed from tube, up to battery chamber, in order to change either WS or NS to L/O (for purpose of either firing torpedo as ordinary electric type or servicing it.  (Acoustic gear not in operation with L/O setting used.)  According to P/W, WS or NS setting is used to prevent torpedo, should its depth-setting be so great as to miss target or for any reason miss target, from returning to endanger U-boat which fired torpedo.  P/W also thought that WS and NS setting ideal for picking up vibrations from other targets than the one originally aimed at.  (Note:  WS or NS setting is made at C.O.'s discretion; prisoner does not know what causes C.O. to order either WS or NS - - whether field of operation, or type of target, or relative position of U-boat (for its own protection) is the determining factor.)  See Also XXXVI.

XXVI.  RUDDERS.

        Starboard turn between eight and eight and a half degrees; port turn between seven and seven and a half degrees.  Same rudder gear as on other electric torpedoes.  Rudder excitation not proportional to intensify of target's propeller vibration;  rudders go all way over under any noise.  Prisoner does not know whether rudders would go over when a single noise (or one crack from the "Spatz" testing gear, concerning which more data follow) is received.  When, during initial straight run, propeller vibrations are picked up, torpedo continues on straight run (distance not

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know by P/W); then rudders go all way over (port or starboard, depending on target's position) and remain locked.  If no propeller sounds audible, rudder remains locked and torpedo either circles in same track (NS setting) or completes original turn and then continues forward course (WS setting).  On turns - - or at any part of a circle - - the torpedo will, on picking up vibrations, turn immediately.  Only on a straight run - - initial straight run or on subsequent straight runs (when WS setting used) will there be a lapse between the receiving of vibrations and torpedo's turning.  Torpedo circles three hundred and sixty degrees, measures from position where rudder first thrown.

XXVII.  TRIAL DATA.

        Off Gotenhafen; between June-July 1943.  P/W one of observers on the 3000-4000 ton target ship which he thinks was the HOLZAPPEL.  Night firing tests with practice warhead fitted with headlight.  Speed of target ship varied between eight and seventeen knots.  Three torpedoes fired at three different times.  Torpedo angles:  zero, ninety, and one hundred eighty degrees.  No noise maker trailed by target ship.  All torpedoes set deep enough (twelve meters) to pass under target.  Distance between U-boat and target about twenty-five hundred meters at all times.  Speed of all three torpedoes:  twenty knots - - constant.

(1)

First torpedo fired on angle; target going away from the U-boat; speed of target about twelve knots.  When about one hundred and ten meters off starboard quarter, torpedo turned to port where, still hearing propeller noises, it turned to starboard about twenty meters off stern and passed under target amidships.

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	(2)	Second torpedo deliberately aimed badly in order to demonstrate how the acoustic mechanism failed to pick up the propeller noises when target too far away.  This torpedo so aimed as to keep it between two hundred and four hundred meters away from the target.
	(3)	Third torpedo fired when target's speed about seventeen knots; target approaching U-boat almost bow on.  Torpedo followed course on target's starboard side; when near the stern, it turned around stern and passed under ship between quarterdeck and stern.  (Note:  This torpedo was closer to the stern when speed of approaching target was seventeen knots that it was when speed of departing target was about seven knots.)

First torpedo set on NS; third torpedo set on WS; neither continued to pursue target.

XXVIII.  SAFETY MEASURE.

        Torpedo not receptive to vibrations before pistol is armed.  Acoustic mechanism becomes armed (i.e. ready for operation) at a distance farther than pistol-arming distance.  (P/W does not know range from U-boat when acoustic gear is armed - - only that it picks up vibrations between one hundred and two hundred meters from target.)

XXIX.  METHOD OF OPERATION.

        According to P/W, T-IV was constructed in order to provide a torpedo which, even if badly aimed, could hit its target.  Torpedo is fired with a definite firing angle (ninety degrees right or left is maximum) and runs toward target on estimated lead angle.  If torpedo is badly aimed so

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that it misses target but is near it, then the acoustic gear goes into action.  The two transformers (fed with three to four volts by the generator) form two lines of current - - one to port and one to starboard.  On receiving a noise to port, for example, the current of the port transformer is disturbed and an induction current is produced which is then amplified about .003 (point zero zero three) volts.  The amplifier current then flows over the "Amsel" to the particular relay which activates the side of the steering mechanism and, in connection with the steering mechanism, causes the rudder to go in the end position.

XXX.  COURSE AND TACTICS OF TORPEDO.

	(A)	Torpedo approaches propeller as close as possible so that, when torpedo turns around stern, it will hit target amidships.
	(B)	Against slow-moving target (about ten to twelve knots) torpedo is farther away from propeller (before torpedo turns) than against a faster target (about fifteen to seventeen knots), when torpedo is closer to propeller before torpedo turns.
	(C)	Against a departing target, torpedo heads for propeller; on receiving propeller vibrations, torpedo will turn (port or starboard, depending on which side vibration received).  If target goes beyond acoustic range, torpedo will either complete its turn and describe successive circles (NS setting) or complete turning circle and continue on forward straight run (WS setting).  If, after first turn of torpedo, target is still in acoustic range, torpedo will again turn (to opposite side from which vibrations previously heard).

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	(D)	Against an approaching target, the torpedo will turn port or starboard (depending on which side of target torpedo is fired), will turn around stern and tend to hit target between quarterdeck and stern.  (Prisoner believes that a destroyer going no more than fifteen knots can be hit in this way, assumption being that, while keeping contact with a U-boat, destroyers would be going between fourteen and fifteen knots.
	(E)	Torpedo need not turn around stern of target; it mat turn port or starboard into midship or stern of an approaching target.
	(F)	Loudness or softness of propeller vibrations have no influence on torpedo's turns; torpedo turns on every intensity or vibrations.
	(G)	Prisoner believes that if target increases speed and zigzags at time that torpedo begins to turn, chances are that target will have gone beyond acoustic range, and torpedo no longer able to pick up vibrations.  (Note:  Torpedo cannot hear backward.)
	(H)	Prisoner has heard of a "Registrear" or "Regulier" (regulating gear) which controls the time or place when, after initial run, torpedo turns in direction of target's propeller.  This gear may have been contained (prisoner is not sure) in a small box inside the amplifier.  He has seen it removed at the base; he had never seen it touched on

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board U-boat; he believes this gear used only during practice runs.  (It is possible - - although prisoner does not know - - that this gear determines the distance from the U-boat (after pistol is armed) when the acoustic gear becomes armed, i.e. ready for operation.)

XXXI.  BULKHEADS.

	(A)	Separates transformers from amplifier; about two and one half inches wide.
	(B)	A derby-shaped cavity into which amplifier is inserted; shaped concave looking forward; made of copper or brass; distance from end of amplifier to center of cavity, about two inches; distance from (each) side of amplifier to side of (each) cavity, about .2 (point two) inches; no rubber or shock absorbers between amplifier and any part of cavity; layer of rubber between amplifier and Bulkhead (A).  P/W not sure whether cavity arrangement designed for protection against own U-boat noises,  Explosive charge extends to both sides of amplifier.

XXXII.  TESTS.

(A)

Rudders:  At base, before acoustic torpedoes are taken on board U-boat, a test is made to make certain that the rudder gear is in good working order.  A box (cover-name is "Spatz"), which produces crackling noises, is moved around in front of the torpedo's nose.  The "Spatz" is operated at a distance of about twenty inches from the nose of the torpedo.  If everything is in order, the rudder turns in the

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		direction of the noise.  This test, which prisoner saw made at Gotenhafen and which is made at all the French bases, is not done in the water.  At no time do the rubbers lock, because the "Amsel" (G-switch) is not set either on NS or WS but on L/O, L/O setting cuts out all acoustic gear.  This L/O setting does not mean that torpedo, if fixed on L/O, would be a true homer; rudders move in test with L/O setting because the acoustic gear is activated by the "Elster" ger and not the gear itself in the torpedo.  (At one time, the prisoner, out of curiosity, scratched across the right side of the nose with his finger nail; the rudder turned to the right all the way over; scratching was constant.  Prisoner does not know whether one crack - - instead of a crackling noise - - will cause the rudders to turn.  Measurements of "Spatz": length, about seven inches; width, about five inches; depth, about four inches; on right-hand top side is a lever which winds a spring; a knob (front, slightly above center) is pushed down and the crackling noise is emitted.  "Spatz" is attached to nose-cap by means of two leather-covered metal straps.  For this test, the battery which supplied the current for the transformers and the amplifier (and from amplifiers to the relays) is the battery used in the "Elster" gear,
		P/W was present at "Spatz" test made in Brest about six days before departure of U-664 for her last cruise.  The

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		torpedoes so tested were then assigned to U-664 and taken on board soon after.  At end of "Spatz" test, the Elster is is removed before the "Spatz" is turned off.  PW believes that is "Spatz" were turned off first, the rudder would return to the zero setting.  PW thinks this is only logical, as no current would be directed to steering apparatus.  The "Spatz" was held in front of the nose of the torpedo and moved through an arc of 150 degrees.
		"Spatz" (box) is attached to torpedo as follows:  a leather covered metal strap is attached (at every ninety degrees) around the warhead (approximately around bulkhead (A)); each curves outward to front of nose-cap; the four straps act as a kind of basket.  On top strap is attached a second strap by means of a swivel (approximately over transformer); a second swivel-guided strap is found 1800 around from first strap; each of these two straps, which extend beyond the four-strapped basket arrangement, are attached to the"Spatz" (box) - - one on each side.

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	(B)	Electrical:  The "Elster" (another cover-name) is used at the base to test all circuits in the torpedo.  "Elster" is a wheeled apparatus consisting of two parts:  (a) a forward box (top of which is on an incline) containing several switches on the outside front, several gauges on the sloping top (which show whether all circuits are operating - - tested for AC and DC currents), and resisters inside; (b) behind box is battery, same kind as used in torpedo.  Length of forward box, about two feet; width, about twenty-eight inches; height, about four feet and nine inches.  Electrical testing done at side of torpedo and, as with "Amsel" test, is done before torpedoes are taken on board U-boat.  Connected by means of a plug in the motor chamber of torpedo.  During this test, all the air-tubes are in operation, the starting lever having been so set.  (Air is for gyro, for steering mechanism, for depth mechanism and for main switch in motor chamber.)  Propulsion motor of torpedo remains out of action, as the battery switch is set on "Charge" (not on "fire").  There is also a box in the motor chamber, connected to Elster during tests.  Elster plug has 8 (more or less) prongs.  PW thinks the Elster has a generator in it, but he has never seen for himself.  The sort of noises the elster made led him to believe this.
	(C)	Motor:  Tested along with "Amsel" and "Elster tests.  NS and WS settings on "Aus" (out) position (i.e., L/O/).  Motor tested for one hundred and twenty-five amps.  Acoustic gear

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		switched off during motor test.
	(D)	Miscellaneous:  Prisoner knows of no supersonic tests; all tests made in his presence were with audible sounds.

XXXIII.  U-BOAT TACTICS.

        Prisoner is certain that no signals are sent out to other U-boats in vicinity when acoustic torpedoes fired; warnings sent out only when F.A.T.s are fired.  Torpedo in stern tube used most against escorts; torpedoes in bow tubes used mostly against convoys.  U-boat does not dive after firing acoustic torpedoes.  Can be fired  while U-boat submerged; up to 100-meter depth (as with any other torpedo).  Never fired in spreads.  U-664 fired acoustic torpedo at aircraft carrier CARD; did not strike target.  P/W explains miss as follows; range and speed of target not correctly estimated; carrier too far away for acoustic apparatus to be activated before end of torpedo's run; moreover, C.O. may have thought (as crew was led to believe) that target was a tanker.  U-boat fired from surfaced position; estimated distance between U-boat and CARD, thirty five hundred meters; angle, ninety degrees.

XXXIV.  MISCELLANEOUS.

        Prisoner is certain that no part of the torpedo is an imitation of an Italian model.  He knows of no acoustic torpedo that would be considered a true homer (but see under Developments).  Has heard of microphone-type of torpedo but does not believe it was ever in actual use.

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Has never heard of acoustic detonation.  No net-cutters and no anti-roll device on T-IV.  Can be fired only by U-boats and Destroyers.  Cannot be fired in wind force of eight.  Has heard from a torpedo testing officer that an air torpedo would create too much noise for acoustic gear.  Two 500-tonners (with T-IV torpedoes) left Brest about 22 July 1943 (U-664 left Brest about two days before.).

XXXV.  COUNTER-MEASURE.

        No attempts made at Gotenhafen trials to counter-mine torpedo.  Prisoner believes that depth-charge can detonate the torpedo; also suggested use of trailed noise makers.

XXXVI.  EMBARKING ON U-BOATS.

        After torpedo taken on board, pistol is inserted; battery switch set on "Schuss" ("Fire").  While being brought on board, torpedo set on L/O by means of a safety key which sticks out of the torpedo about two and a half inches.  When torpedo put into tube, key must be removed; when this key is turned, a spring ejects it, and, at the same time, the switch is automatically thrown to WS; in this (WS) setting, torpedo is put into tube; while in tube, setting to NS may be made by means of the usual setting gear on tube.  This setting procedure is in accordance with standing order; purpose is to ensure that torpedo men know exactly what setting each torpedo has when it is in the tube.  Prisoner believes that original setting could - - only on order - - be on NS instead of WS.  Safety key kept on board, and when torpedo is to be serviced, same key is used to turn switch to L/O (torpedo withdrawn from tube).  Depth-setting first set for twelve meters and then put into tube; setting changed, after torpedo withdrawn from tube, from twelve to three meters (or to any

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        No servicing of the acoustic gear is done on board.  PW says that the mechanism is so carefully and solidly constructed as to require no servicing on board.  This is true even in the case of larger U-boats that stay out much longer than U-664 ever did.

XXXVIII.  GYRO STEERING APPARATUS.

        The gyro steering apparatus of T-IV consists of the following parts:  the housing (1), which is of cast brass.  The upper part of the housing received the steering piston (2), which is connected with the rudder rod (3).  On both sides of this housing are two small bore-holes which let the entering air escape slowly.  On this housing are fitted two relays (4) which, in connection with the connecting piece (11), activate the slide (9), whenever the sound receiving apparatus is in operation, and cause the air flowing from the air conduit (10) to go into the port or starboard air canal.  On the starboard side of the steering apparatus are two equalizing springs (6) which intercept the stroke when there is any movement

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of the piston (2), which stroke would, in straight run, otherwise be transmitted to the slide (9)  (NOTE:  P/W explained that on straight run the equalizing springs keep the piston centered and the torpedo on a straight course.  When, for turns, one of the relays is activated and moves the slide (9), the power of the relay is greater than that of the springs; this holds the slide in position to direct the air-current on the desired side by the piston).

        Mode of action:  The torpedo is fired.  At the same moment the steering apparatus receives, via a pressure regulator, and air pressure through the air conduit (10) and, when the torpedo is on straight run, goes through the slide (9) behind both sides of the piston (2) in equal amounts.  In case of a slight digression of the torpedo, the jet pipe (10) in connection with gyro would be moved over a so-called anchor and rod, and more air would flow into the particular (starboard or port) hole of the slide.  The air then causes the piston to go into the desired direction.  The resultant excess of pressure on the other side can escape through the small bore in the housing.  The movement of the piston (2) then goes over the rudder rod (3) to the gyro rudder.  While the torpedo resumes its former course, the same stroke of the rudder rod transmits itself over the cam (7) and the connecting rod (5) to the slide (9).  The latter follows the jet-pipe so that a too sudden throwing of the rudder is prevented.  When, after a rather long run of the torpedo, the sound-receiving gear comes into operation and one of the relays (4) is activated, then a small plate is attracted through the resulting electro-magnetism, thus

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causing the slide (9) to go via a transmission (11) into the particular direction.  The air from the jet-pipe then flows into only one of the two air canals, so that the piston goes into its end position, which operation is transmitted to the rudder.  The slide (9) is prevented from slipping back by the two springs (6) and the cam (7) which is displaceable between the two springs, as the power of the relay overcomes the pressure of the springs.  The stroke of the piston is thus taken up by the springs (6).  When the other relay comes into operation the same procedure applies.

DEVELOPMENTS.  ("Zaunkönig")

I.

        A new type of acoustic torpedo (known as T-V) is said to be in use.  Electrically driven; speed of twenty-five knots - - constant; greater range.  Prisoner thinks that T-V (T-5) may be a true homer (i.e., pursues propeller of target without circling) and that construction, details, etc. may be same as in T-IV.  About eight days after U-664 left Brest for her last patrol, a 750-ton U-boat left same base (about end July 1943) with T-V torpedoes.  T-V torpedoes require no change in torpedo tube construction.

II.

        Cover name of T-V (acoustic torpedo) is "Zaunkönig" (wren).  The following questions asked of P/W could not be answered.

        (1)  Whether core winds primary or secondary.

        (2)  Whether generator delivers AC or DC to transformers.

        (3)  Whether transformers must be adjusted individually.

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        (4)  Dimensions and number of turns of primary and secondary wires.

        (5)  Whether distance from transformers to bulkhead is critical.

        (6)  Frequency.

        (7)  Frequency at which torpedo most sensitive.

        (8)  Type of electrolyte.

        (9)  Whether primary of transformer actuated by AC or DC.

F.A.T. TORPEDOES.

I.  TWO TYPES.

        (A)  F.A.T. (FAT-Ato; air driven)

                1.  Ranges and speeds

	a.	14,000 meters at 30 knots:  WS (Weitschuss - - distant shot); this setting always used.
	b.	8,000 at 40 knots:  NS (Nahchuss - - near shot)
	c.	6,000 meters at 44 knots:  SS Schnellschuss - - fast shot).

                2.  Angle X always ninety degrees:       

                                                                                                

                3.  Diameter of turning semi-circles:

                        a.  Maximum:  140 meters.

                        b.  Minimum:  80 (or 90) meters.

                             (NOTE:  Diameter of semi-circle is either 140 meters or 80 (or 90) meters and is determined on land - - not made or changed while torpedo is on U-boat.)

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                4.  Settings:

	a.	"Schleife rechts lang" (long leg to right).
		i.  About 500 meters, measured from end of turn to start of following turn.
	b.	"Schleife rechts kurz" (short leg to right).
		i.  About 300 meters, measured from end of turn to start of following turn.
	c.	"Schleife links lang" (long leg to left).
	d.	"Schleife links kurz" (short leg to left).

                5.  Initial straight run ("Vorlauf").

	a.	Can be set from 400 meters to 14,000 meters.  (obviously no turns possible with a 14,000-meter initial straight run.)
	b.	Setting made according to estimated distance to target; if target, for example, is 1,000 meters away, straight run will be set for somewhat over 1,000 meters - - about 1,050 meters.
	c.	Setting of initial straight-run mechanism independent of leg-mechanism.  (Number of legs made by torpedo depends (obviously) on length of initial straight run.)

                6.  Spreads:

                        a.  Leg settings for spreads.

                                  i.   Spread of two:  1 long, 1 short.

                                  ii.   Spread of three:  2 long, 1 short; or 1 long, 2 short.

                                  iii.  Spread of four:  2 short, 2 long.