S E C R E T

NAVY DEPARTMENT

OFFICE OF THE CHIEF OF NAVAL OPERATIONS

WASHINGTON

Final Report - G/Serial 30

REPORT ON THE

INTERROGATION OF SURVIVORS FROM U-231

SUNK 13 JANUARY 1944

S E C R E T

TABLE OF CONTENTS

				Page
CHAPTER	I.		INTRODUCTION	1
	II.		DETAILS OF U-231	3
	III.		TECHNICAL DETAILS AND PROCEDURES	10
	IV.		TACTICAL REMARKS	17
	V.		CREW OF U-231	20
	VI.		EARLY HISTORY OF U-231	24
	VII.		FIRST PATROL OF U-231	27
	VIII.		SECOND PATROL OF U-231	35
	IX.		THRID AND LAST PATROL OF U-231	39
	X.		SINKING OF OF U-231	42
	XI.		OTHER U-BOATS	48
	XII.		MORALE	63
ANNEX			CREW LIST OF U-231 AND U.S. EQUIVALENTS OF GERMAN NAVAL RANKS

CHAPTER I.  INTRODUCTION

        U-231 was sunk by several well placed depth charges dropped by Wellington L/172 at about 2230 Z, 13 January 1944, in position 44.15 N, - 20.38 W.  The 500 ton U-boat was commanded by Kapitänleutnant Wolfgang Wenzel, who had commissioned the boat on 14 November 1942.  U-231 had been at sea for a total of 121 days and had been singularly ineffective, never having sunk anything.  She was sunk while underway 18 days on her third patrol.

        The entire crew of 50 escaped from the sinking U-boat, but seven men died of exposure or drowning.  Forty-three men, including the commander, the executive officer, the 2nd watch officer, the engineering officer, and the doctor were rescued by U.S.S. PARROTT and U.S.S. BULMER.  The prisoners were later transferred to U.S.S. BLOCK ISLAND which landed them at Norfolk 3 February 1944.  After a brief interrogation of the entire crew 14 prisoners were brought to an interrogation center.

        The progress of the interrogation was slowed considerably by the extreme security-consciousness of the prisoners.  This was partly due to the fact that Kapitänleutnant Wenzel was a rabid Nazi and that many of the younger members of the crew were deeply steeped in Nazi ideology.  Morale had also been boosted by the alleged sinking of an Allied destroyer just one day prior to their own sinking.  In due course, however, interrogation proved fruitful.  

 

        U-231 was the first U-boat equipped with the new automatic

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37 mm. gun from which prisoners were taken.  Much information regarding the new weapon was obtained.  However, the prisoners from U-177, which was sunk on 6 February, were able to elaborate on the features of the automatic 37 mm. gun, and, in view of this, all information gained will be published in the interrogation report on U-177.

        The special features of this report are contained in Chapters III and IV.  Attention is drawn to the new H/F D/F set, to the procedure of A/C and U-boat cooperation, and to the complete drawings of the radio room and listening room aboard U-231.

        U.S. Navy equivalents of German ranks will be found in the Annex.

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CHAPTER II.  DETAILS OF U-231

TONNAGE

        500 tons.

TYPE

        VII-C.

BUILDING YARD

       Germania Werft, Kiel.

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DISTANCE FROM PRESSURE HULL TO DECK GRATING

        Normal.

MAXIMUM DEPTH ATTAINED

        220 meters.

CRASH DIVING TIME

        29 seconds to 15 meters.

BRIDGE ARMOR

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AMMUNITION

        (a)  For 20 mm. guns:  5,000 rounds carried.  New type of ammunition may have been carried.  (See Chapter III).

        (b)  For 37 mm. automatic gun:  New ammunition with high explosive power.  Referred to as "Minemunition" (mine ammunition).

        (c)  For demountable machine guns:  10,000 rounds.

READY AMMUNITION LOCKERS

        One pressure-proof ammunition locker aft of periscope housing; 4 lockers located between Platforms I and II, 2 over 2.

TORPEDO TUBES

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TORPEDO STOWAGE ON LAST PATROL

        2   F.A.T.-2 torpedoes in tubes 1 and 3.

        2   T-5 torpedoes in tubes 2 and 4.

        1   T-5 torpedo in tube 5.

        1   T-3 torpedo above floor plates in forward torpedo compartment.

        1   T-3 and 3 F.A.T.-1 torpedoes under floor plates in forward torpedo compartment.

        1   T-5 torpedo on floor plates in stern torpedo compartment.

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installed after return from the third patrol.  (See also Chapter III).

DIESELS

        Two G.W. 6 cylinder, 1400 h.p. Diesels.  R.P.M. speeds practically identical with the installation in U-664 (G/Serial 27).

SUPERCHARGERS

        Two "Kapselgebläse"  (Roote's type).

FUEL OIL CAPACITY

GERMAN ASDIC

        Not fitted.

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RADAR

        Not fitted.  U-231 was originally equipped with a radar set, the dipoles being fitted around the forward part of the conning tower.  After the first patrol the set was dismantled, but the dipoles were only removed after the second patrol.  The rods to which they had been fastened were left in place.  The radar was never used while on patrol.

RADAR DECOY BALLOONS

        Carried in 4/5 boxes.  One balloon was recovered by U.S.S. BULMER about 20 miles north of U-231's survivors' position.  (It is doubtful that this had belonged to U-231.)

G.S.R.

        Wanz G-2, 2 "Naxos" sets, and a "Borkum" set.  The G.S.R. sets covered the following wave bands:  Naxos:  8 - 12 cm; Borkum:  30 - 300 cm;  Wanz G-2:  120 - 180 cm.  (See also chapter III).  On first patrol U-231 carried a Metox R 600 with cross-type aerial.  On second patrol a Wanz G-1 was fitted.

D/F GEAR

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        (c)  40 watt emergency transmitter fitted.  This was used frequently in the Bay of Biscay on certain short waves not well suited for the 200 watt transmitter.

        (d)  U.K. gear not fitted.

REMOTE TRANSMITTER CONTROL PANEL

        Fitted - See Plate VI.

UNDERWATER TELEGRAPHY

        Fitted.  Used once in mid-Atlantic to contact another U-boat making a diving test.  However, no reply was received.

RECEIVERS

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CHAPTER III.  TECHNICAL DETAILS AND PROCEDURES

REMARKS ON T-5 TORPEDO

        T-5 torpedoes carried by U-231 had the plastic nose filled with liquid, not the type open to sea water carried by U-172.

        It was stated that these torpedoes are so sensitive as to be easily rendered useless by the explosion of depth charges in the vicinity of the U-boat, even when the U-boat itself sustains little or no damage.

        The propellers of T-5 torpedoes were said to be the same as those on any ordinary electric torpedo.

        The entire top surface of T-5 must be kept free of grease.  The body of the torpedo was stated to be homogeneous, of metal, no plastic, and without any inlaid strip along the top.  T-5 torpedoes carried on U-231 were withdrawn from the tube part way for charging only; when the charging was finished, the cover plate was wiped.  T-5 torpedoes were never withdrawn entirely from the tube for wiping.  This would have been done only if water were admitted to the tube and then expelled.  No reason could be advanced why the top surface of the torpedo was to be kept free of grease.  A rating was told to be careful of the torpedo at all times and to be especially careful to protect the nose while loading.

DEVELOPMENT OF A T-6 TORPEDO.

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T-5 but with increased speed and range.

SETTING OF FAT TORPEDOES

        F.A.T. torpedoes in tubes were on setting Right Long, 14,000 meters.  U-231 never fired and F.A.T. torpedoes.

INSTRUCTION ON F.A.T. AND T-5 TORPEDOES

        Torpedo-room personnel on U-231 were not aquatinted with this torpedo, nor with T-6.  Instruction given the torpedo petty officer of U-231 was sketchier than has been the case with other U-boats.  His F.A.T. instruction was confined to a short lecture by the flotilla torpedoman at La Pallice, probably in June 1943.  Instruction consisted only of servicing and setting and included no details of track except the a brief description of "Curly" course run by F.A.T-1.  His instruction in T-5 took place in Gotenhafen in July 1943.  He did not, unfortunately, take the whole course.  He attended two morning lectures on care and servicing of T-5, but was never present at firing trials.  He was shown no models, drawings, nor sketches of the torpedo's track.  He never saw nor made a Spatz test.  His knowledge was, therefore, considerably less extensive than that of any other torpedo petty officer recently interrogated.

TESTS OF COMBINATION PISTOLS

        All pistols carried by U-231 on her second and third patrols had combination impact-magnetic firing.  The magnetic apparatus was tested by the flotilla torpedoman in La Pallice

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before the start of each patrol.  No further test was ever made on board.

NEW TYPE OF MACHINE GUN

        One prisoner mentioned a new type of 15 mm. machine gun, said to have a theoretical rate of fire of 1,000 rounds per minute.  Whether and, if so, when this new type would replace the demountable machine guns now carried by U-boats could not be ascertained.

NEW 20 MM. AMMUNITION

        The new type of 20 mm. ammunition is known as "Ölbrandmunition (Oil incendiary ammunition).  U-231 may have carried this new type among other types on her last patrol.

        It was described as armor-piercing and explodes as an incendiary thereafter.  It has a pointed nose, has tracers up to 2,000 meters, and is self-destroying at 2,500 meters.  The prisoner who saw experiments at Mimizan described the explosion, after piercing the armor, as a flash of vivid orange flame.

NEW U-BOAT ARMAMENT

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        (d)  One 6-barrelled rocket projector aft on the bridge.  This device was claimed to be capable of firing in any direction.  The rockets are said to be inserted from the top and are electrically fired.  Coxswains and boatswains are now being trained to operate rocket projectors.

        (e)  Usual demountable machine guns on the bridge.

REMOTE CONTROL FIRING

        A radioman stated that he had never heard of remote control firing on U-boats.  He doubted very much whether any such developments are contemplated.

REMARKS ON G.S.R.

        (a)  Wanz G-2.  Covers a wave band from 120 cm. to 180 cm.  It is identical with Wanz G-1 except that radiation had been eliminated; consequently no telegraph key such as was fitted on U-841 was needed.  (See G/Serial 28).  Wanz G-2 is fully described in G/Serial 29 on the interrogation of survivors from U-172.  One of the radioman of U-231 stated that Wanz G-2 was a very delicate instrument and was easily put out of order.

        (b)  Naxos.  U-231 carried 2 Naxos sets.  Each set was used for three days at a time.  Two Naxos aerials of the usual type were carried.  The aerial had to be rotated continually while in service.  A wave band from 8 cm. to 12 cm. was covered; the practical range was said to be 15 kilometers.

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picked up by Borkum were heard through the Radione set.  The Borkum carried on U-231 was identical with the set carried by U-172 and is described fully in G/Serial 29.

G.S.R. SEARCH PROCEDURE

        Procedure on U-231 was to operate both Naxos and Wanz G-2 simultaneously.  If a signal was obtained on Wanz G-2, Borkum was connected to the drum-shaped aerial in place of Wanz G-2.  If a tone was then heard on the Radione set, Borkum was disconnected from the aerial again.  If the tone was then still heard on the Radione it was proof that the signal was being received by the Naxos set which remained connected to the Radione set.  Of course, if a tone had been heard on the Radione set in the first place, i.e., before the Borkum was connected to the drum-shaped aerial, this was an indication that Wanz G-2 had picked up the signal.

        It seems definite that German U-boats attach the greatest importance to the continuous observation of the 10 cm. wavelength.

NEW LORENZ H/F D/F SET

        A new H/F D/F set manufactured by Lorenz was installed on U-231 prior to her last patrol.  The set was referred to as "Zwischenfrequenzpeiler".  It was mounted in the radio room in place of the former D/F set.  (See No. 4, Plate I).  This set, as well as the long wave D/F apparatus, is supplied by one power pack, and either set could be supplied by simply throwing the switch.  The plate current for the H/F D/F is 5 to 7 volts.  The actual upper limit of the frequency covered by this set was not established, but

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the primary purpose was to D/F voice traffic on 124 meter wavelength.  It was believed, however, that the range below 124 meters was greater than that above 124 meters.  U-231 had no opportunity to use this set on her last patrol.

        In order to use the D/F loop for the new set, the windings in the loop were changed.  A radioman was under the impression that all but two of the windings were removed.  A special, radiating rod aerial ("Strahler", see also Plate VII, page 25, G/Serial 27), to serve as compensator for the D/F loop was mounted forward on the bridge.  The forward jumping wire aerial is used as compensator for the L/F D/F set.

NEW RADAR EQUIPMENT

        A radioman stated that, in the future, U-boats will be equipped with "Hohentwiel" radar sets.  This type was formerly used by G.A.F. and is being adapted for use in U-boats.  The set was said to operate on a wavelength of 50 cm.  In addition to the mattress type aerial, U-boats carrying "Hohentwiel" radar will also carry a drum-shaped aerial mounted on an extensible rod, thus permitting all-round search at periscope depth.  The dipoles of the drum-shaped aerial are believed to be shorter than those used on the drum-shaped G.S.R. aerial.  It was believed that U-boats equipped with "Hohentwiel" radar would no longer carry any G.S.R. gear whatsoever.

MULTI-UNIT HYDROPHONES

        The Multi-Unit Hydrophone set (G.H.G.) fitted on U-231

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had a dial which could be set to 0-500-1000-2000-3000.  It was stated that these settings affect the pitch of the tone heard.  Propeller sounds of destroyers were heard best in the 500 setting.  If the dial was set higher than 500 the sound became a high-pitched whine and was finally almost inaudible.

ARANGEMENTS OF RADIO AND LISTENING ROOMS

        The arrangements of the radio and listening rooms aboard U-231 are shown in plates I to V.

NEW ARRANGEMENTS OF RADIO AND LISTENING ROOMS

        It was stated that as of February 1944 the radio and listening rooms aboard U-boats will be rebuilt and rearranged.  New equipment, including a depth charge plotter and counter, will be added.

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CHAPTER IV.  TACTICAL REMARKS

ANTI-AIRCRAFT TACTICS

        It was stated that U-boats will not dive when an airplane has approached closer than 8,000 meters.  The officer on the bridge is responsible for estimating the distance and deciding whether the boat will dive or will fight it out on the surface.  Prisoners confirm that U-boats are in particular danger from A/C just after they have dived even though the U-boat makes an immediate turn to port or starboard.

U-BOAT AND A/C COOPERATION

        When U-231 was on her last patrol, operating in the group of U-boats stretched from Cape Finisterre to the Azores, she was instructed by Control to listen for A/C beacons for 3 days at 0800 and 2000.  The transmissions were said to be on a frequency of 385 kilocycles.  U-231's approximate position was 42 N. - 15 W.

        It was claimed that it is now the practice of U-boat patrol lines, operating in cooperation with German aircraft, to remain submerged almost continually.  The spacing between the U-boats was said to be about 20 miles.  Aircraft search for an expected convoy and, upon sighting, report to Control.  U-boats are required to listen at stated intervals (Programmzeiten) to transmissions from Control, either at periscope depth or upon coming to the surface.  They may then receive instructions either to proceed to a given position or to listen for aircraft beacon signals.

        Since experience has shown that positions given by A/C are known to be unreliable, Control will then generally instruct

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the A/C to transmit a beacon signal.  Thereupon each U-boat reports the bearing on which she has heard the A/C beacon, together with her own position.  From the information Control plots the exact position of the A/C (i.e. the Convoy) and issues the necessary orders to the U-boats which are to participate in the attack.

        Simultaneous attacks of U-boats and A/C against convoys have not been heard of by prisoners.

PASSAGE REPORT

        When passing 20⁰ W.  U-boats must report to Control.  Formerly this passage report was made at 15⁰ W.  Only if a U-boat has just previously been called to report position and stock of fuel on hand, may the passage report be omitted.

RADIO INTELLIGENCE ON U-BOATS

        A radioman stated that the practice of adding radio intelligence operatives to U-boat crews has been discontinued.  Experience had shown that the intercepted voice traffic was of relatively little value.  It is deemed more important to D/F these transmissions disregarding the contents of the transmission.  It is felt that the purpose of D/F'ing is amply served by the installation of the new H/F D/F Lorenz set, described in Chapter III.

U-BOATS IN THE BALTIC

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U-boats were said to have been kept in the Baltic.  The only reason advanced for this accumulation of boats was that the boats were waiting for new equipment such as the Wanz G-2 G.S.R. set and the new automatic 37 mm. gun.

ESCORT MEETING POINT

        U-boats entering or leaving La Pallice have an escort of a mine destructor vessel from or to a point identified as "Punkt Gabel".  This was stated to be on the 50 meter line.  It may serve more than one base and probably included the Bordeaux base.  A radioman was under the impression that the name of the meeting place would be changed frequently.

REPLACEMENT OF QUADRUPLE 20 MM. MOUNTS.

        It was stated that in the future all U-boats on operational patrol will be fitted with the new automatic 37 mm. gun instead of the 20 mm. quadruple mount.  The latter had proved unsatisfactory as the training and elevating mechanism was easily damaged by the corrosive action of sea water.

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CHAPTER V.  CREW OF U-231

TOTAL COMPLEMENT

        U-231 had a total crew of 50 on her last patrol.  This included the captain, 2 line officers, one engineer officer, one doctor, 15 petty officers, and 30 enlisted men.  Two petty officers and 5 enlisted men did not survive the sinking.

OFFICERS

        With the exception of the doctor the officers on U-231 had been with the boat since her commissioning on 14 November 1942.  The doctor took part on the second and the last patrol only.

        Kapitänleutnant Wolfgang Wenzel, of the 1934 German Naval Term, was definitely not the usual type of German U-boat commander encountered by his interviewers.  Apart from being 100% Nazi, stubborn and stupid in his political philosophy, he was highly nervous and confirmed the opinion which most of the crew and his officers had, namely that he was a coward, unfit for the dangerous task of commanding a U-boat.  Almost all prisoners were unanimous in their opinion that U-231 could at least have made an attempt to return to base after she had been attacked on 13 January 1944.  Whether this would have been the wise course is doubtful, but the crew's opinion was based on their previous experiences with Wenzel.  On both previous patrols Wenzel violated the oft-repeated instructions of Grand Admiral Dönitz always to attack.  He had submerged upon sighting ships or convoys giving as his reasons that such encounters were dangerous, due to air cover or to superior escort

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protection.  On three patrols U-231 only fired one torpedo; this was on the day before she was sunk.  The torpedo, aimed at what was believed to have been a destroyer, missed, but an explosion, as yet unexplained, was cited by Wenzel as the proof of a probable hit.

        Prior to entering the Navy in 1934, Wenzel was said to have belonged to the merchant marine for several years.  He is now 34 years old, three or four years older than his classmates.  His history is not well established.  He served as communications officer on Raider 16 which was sunk on 22 November 1941 by H.M.S. DEVONSHIRE.  Wenzel was rescued by a group of U-boats and was probably taken aboard an Italian submarine.  (O.N.I. Note:  This was probably the CALVI commanded by C.d.C. Emillio Olivieri.)  Upon his return to Germany, he volunteered for the U-boat arm.  On another U-boat he made one or two patrols as commander-under-instruction.

        When U-231 was sinking, Wenzel attempted suicide by shooting himself in the mouth.  Unsuccessful as always, he was not able to do away with himself.  The bullet lodged in the back of the neck and was extracted several days later on U.S.S. BLOCK ISLAND.  Few of the crew knew about the suicide attempt as he explained to his shipwrecked companions, while on the raft, that he only suffered from a sore throat.  He did not like to be reminded of it once he was ashore.

        The executive officer was an Austrian, Oberleutnant z. S. Friedrich von Schiefner, of the December 1939 Term.  He was

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23 years old.  His history is not known.  He was reasonably well liked by the crew.  His political beliefs were not necessarily  those of his captain, but he was an ardent advocate of a Greater Germany.

        Leutnant z. S. Joachim Hünefeldt, 21 years old, was second watch officer.  He belonged to the October 1940 Term.  Politically he was violently anti-Nazi, but sufficiently indoctrinated to remain adamantly security-conscious.  The third patrol of U-231 was Hunefeldt's sixth on U-boats.  He had previously served as midshipman on U-751 under Kapitänleutnant Bigalk; the three patrols on that boat had taken him to the East Coast of the U.S. in the heyday of U-boat warfare early in 1942.

        The engineer officer aboard U-231 was Oberleutnant (Ing.) Christoph Geyer, 26 years old, of the October 1939 Term.  U-231 was his first operational U-boat as he had previously only served on school boats.  The few times he was called upon to perform more than routine duties, he acquitted himself well.  The commander must have appreciated this as Geyer was awarded both the Iron Cross 1st and 2nd class after completion of the first patrol.

        Dr. Willi Reinhard, Stabsarzt d. R., was the medical officer aboard U-231.  He was born in 1909.  This was his second patrol since he joined U-231 after her first patrol.  Before being drafted to the Navy, he specialized in pediatrics after having attended the universities of Freiburg and Vienna.  Reinhard was not a full-fledged Nazi and on some occasions even voiced outspoken anti-Nazi sentiments, which were apparently not well received by

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Wenzel.  He was not sure why a U-boat carried a doctor as he only once had occasion to make use of his profession.  This was when three men from another U-boat were rescued in the North Atlantic in October 1943.

PETTY OFFICERS

        Among the petty officers the chief quartermaster, Albert Borck, 31 years old, was outstanding from a point of service.  He had made a total of 15 patrols, although U-231's last patrol was his first patrol on her.  Previously he had served with Kapitänleutnant Guggenberger on U-81.  He had been decorated with the German Cross in Gold.  He was pleasant but extremely security conscious.

        It was again confirmed that among a U-boat's crew this group of men has by far the most to offer and several of them responded well to the efforts of the interrogators.  Among them in particular Wenzel was disliked and distrusted. 

        The average age of this group was 24-1/2 years.

ENLISTED MEN

        Few groups of U-boat prisoners have been encountered on this side of the Atlantic with as low an I.Q. as this crew.  The average age was 21 years.  Their stupidity was only surpassed by their desire to keep whatever little they knew hidden from the interrogators.  Only Goebbels' teachings were well known and willingly spouted at the least provocation.

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CHAPTER VI.  EARLY HISTORY OF U-231

COMMISSIONING

        U-231 was commissioned 14 November 1942.  A small celebration was held at which the commander of the 5th Flotilla, Korvettenkapitän Möhle and the father of U-231's commander were present.

U.A.K. TRIALS