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C.B.  04051 (95)
"U 73"
Interrogation of Survivors
February, 1944
This Report is not to be considered accurate in all respects, having been prepared before complete information was available.  It is therefore not to be taken as historically correct.



          This book is the property of His Majesty's Government.  
          It is intended for the use of the recipients only, and for communication to such Officers under them (not below the rank of Commissioned Officer) who may require to be acquainted with its contents in the course of their duties.  The Officers exercising this power will be held responsible that such information is imparted with due care and caution.  



Attention is called to the penalties attaching to any infraction of the
Official Secrets Acts.
C.B.  04051 (95)
"U 73"
Interrogation of Survivors
February, 1944
  N.I.D. 0671/44.  


          The following report is compiled from information derived from prisoners of war.  The statements made cannot always be verified; they should therefore not be accepted as facts unless they are definitely stated to be confirmed by information from other sources.  


  Introductory Remarks  
    (i)  General;  (ii)  Commanding Officer;  (iii)  Complement of "U 73";  (iv)  Equivalent Ranks.  
  Details of "U 73"  
    (i)  Type;  (ii)  Displacement;  (iii)  Builders;  (iv)  Armament (a)  Guns, (b)  Torpedoes, (c)  Torpedo Tubes;  (v)  Diesels;  (vi)  Superchargers; (vii) Compressors;   (viii)  Air Bottles;  (ix)  G.S.R.;  (x)  R.D.B.;  (xi)  S.B.T.;  (xii)  Multi-unit Hydrophones;  (xiii)  Echo Sounder;  (xiv)  W/T Equipment;  (xv)  Rubber Dinghies;  (xvi)  Flotilla;  (xvii)  Base;  (xviii)  Badge;  (xix)  Field Post Number.  
  Fifteenth and Last Patrol of "U 73"  
    (i)  Departure from Toulon;  (ii)  Attack on a Corvette;  (iii)  Flooded Torpedo;  (iv)  Sighting of a Destroyer;  (v)  Collision with another Vessel;  (vi)  Off Algiers on 16th December;  (vii)  Attack on a Convoy.  
  Sinking of "U 73"  
    (i)  Depth-Charge Attack;  (ii)  Gunfire Attack.  
  General Remarks on U-Boats  
    (i)  U-Boat Escort in the Mediterranean;  (ii)  New W/T Signal Procedure;  (iii)  Anti-Aircraft Gunnery;  (iv)  Use of D/F and Radione Sets;  (v)  Reception of Broadcasts;  (vi)  Charging Batteries;  (vii)  Dual Purpose Propulsion Units;  (viii)  German Asdic;  (ix)  K.D.B. Search Gear;  (x)  German A/S Tactics.  
  G.S.R. and Radar  
    (i)  General Attitude toward G.S.R.;  (ii)  Wanze II;  (iii)  Borkum;  Naxos;  (v)  G.S.R. Procedure;  (vi)  General Remarks on Radar;  (vii)  Seetakt type Hohentwiel Radar.  
  Miscellaneous Remarks  
    (i)  Relations between Italians and Germans;  (ii)  Sabotage in Southern France.  
                APPENDIX "A"  Previous Patrols of "U 73"
    (i)  Early History;  (ii)  Sixth Patrol;  (iii)  Seventh Patrol;  (iv)  Eighth Patrol;  (v)  Ninth Patrol;  (vi)  Tenth Patrol;  (vii)  Eleventh Patrol;  (viii)  Twelfth Patrol;  (ix)  Thirteenth Patrol;  (x)  Fourteenth Patrol.  
                APPENDIX "B"  Nominal Roll of "U 73"
                PLATE.  Naxos and Borkum G.S.R.s                                              facing page 6
      Diagram of Connections    
  (C51977)                                                                                                                             B*  


        In C.B. 04051(92), page 6, paragraph 2, a prisoner is recorded to have incorrectly stated that La Pallice was attacked and "SCHARNHORST" hit in 1941 by U.S. aircraft; in fact, the credit for the attack belongs to Halifax aircraft of Bomber Commend.  The United States were not then at war.


          ON 16th DECEMBER, 1943, IN POSITION 36° 09' N., 00° 50' W.  
  (i)  General  
          "U 73," a 500-ton U-Boat, commanded by Oberleutnant zur See Horst Deckert, was sunk on 16th December, 1843, in position 36° 09' N., 00° 50' W., by U.S.S. "Wolsey" and "Trippe."  
          "U 73" was sunk on her fifteenth patrol and, during the course of her long life, claimed sinking of about 120,000 tons of shipping as well as a number of warships.  The first six patrols were made in the Atlantic, the remaining nine in the Mediterranean.  The first of her two Commanding Officers, Kapitänleutnant Helmut Rosenbaum, was regarded as the more successful.  He accounted for most of the tonnage sunk, and was awarded the Knights' Cross for sinking H.M.S. "Eagle" on 11th August, 1942, on his eighth and last patrol.  Deckert, her second commanding officer, made wholly unsubstantiated claims of having sunk a U.S. cruiser and, on his last patrol, two U.S. destroyers.  He has the doubtful honour of landing a French saboteur on the coast of North Africa on his penultimate patrol.  (See Appendix "A.")  
          Features of this report are:  
                  (a)  Details of Borkum and new type Naxos G.S.R.  
                  (b)  new type Radar.  
                  (c)  German Asdic.  
  (ii)  Commanding Officer  
          Oberleutnant zur See Horst Deckert was born in Hanover in 1918.  In 1925, his family moved to Buenos Aires where his father became director of the Seda Lana textile company.  Deckert lived in Argentina until 1936 when he returned to Germany and, in April, 1937, entered the German Navy.  As a cadet he served on board "Schlesien" and made several cruises in her.  He was appointed to "U 73" during the final phases of construction as midshipman and has served in her ever since.  
          Deckert was described by prisoners as an efficient officer with, however, a burning desire to be awarded the Knights' Cross.  They felt that he may have made false claims of tonnage sunk and one of them insisted that he had sunk only four ships throughout his entire career.  
          Deckert was extremely correct with the interrogating officers but refused to divulge any information.  He gave the impression of being a fanatical Nazi.  
  (iii)  Complement of "U 73"  
          On her last patrol, "U 73" carried a complement of fifty officers and men, including a medical officer who was to have been replaced at the end of the fifteenth patrol by a sick berth attendant.  Thirty-four of the ship's company survived the sinking, but one of them, the Second Watchkeeping Officer, escaped with an officer from "U 593."  This was accomplished in Algiers by the simple expedient of hiding in a closet during roll call, while two C.P.O.'s took their places in line.  
          Among the thirty-three survivors who were brought to the United Kingdom, several of them had been disrated for various offenses.  One had been reduced from Sub-Lieutenant to Ordinary Seaman.  They were all extremely secure due in part, to the lack of segregation during transportation from North Africa to the United Kingdom.  Petty Officers and men from "U 593" as well as from "U 73" were accommodated together and held frequent security lectures.  
  (iv)  Equivalent Ranks  
          The following are the Royal Navy equivalents of German Naval ranks used in this report.  
Kapitän zur See Captain.
Fregattenkapitän Commander.
Korvettenkapitän Lieutenant-Commander.
Kapitänleutnant Lieutenant.
Oberleutnant zur See Sub-Lieutenant.
Leutnant zur See Junior Sub-Lieutenant.
Oberfähnrich zur See Senior Midshipman.
Fähnrich zur See Junior Midshipman.
Marinestabarzt Surgeon Lieutenant.
          The suffix "(Ing.)" after a German rank in place of "zur See" denotes an Engineer Officer.  The suffix "der Reserve" denotes a Reserve Officer.  
  (C51977)                                                                                                                              B*2  


  Type VII B, described as differing from VII C in the absence of quick diving tanks.
  Tonnage 500 tons.
  Builders Vulkan, Vegesack (completed trials Autumn, 1940).
  Armament (a)  Guns:  Two twin 20 mm. (0.79 in.) mountings on the upper bandstand; one quadruple 20 mm. mounting on the lower bandstand; two M.G.s 81 on bridge.  There were four ready-use ammunition lockers for the 20 mm. guns, each containing 20 magazines.  Two containers were on each of the two bandstands.  The bridge was not armoured.
    (b)  Torpedoes:  Twelve carried on the last patrol.  Four were stated to be T.5s (Gnats), four were F.A.T.-T.3s (Curlies), and four were normal electric torpedoes.  One T.5 was loaded in Tube II and one was on the port side of the floor plates forward, one was in Tube V and one wa on the floor plates aft.  (For details of the T.5, see C.B. 04051(94), Section VIII.)
    (c)  Torpedo Tubes:  Four bow and one stern.
  Diesels M.A.N.  The cylinder liners had been changed only once, early in 1942.
  Superchargers Exhaust type.  They had never been re-bladed.
  Compressors Two electric compressors fitted.  No Junkers compressor was carried.
  Air Bottles Capacity, 325 litres (11.5 cu. ft.);  pressure, 200 atmospheres (3,000 lbs./cu. in.).
  G.S.R. Wanze II, Naxos and Borkum types carried.  (for details, see Section VI.)  Radar was not fitted.
  R.D.B. Carried but used infrequently.  Two hydrogen bottles for inflating the balloons were on either side of the conning-tower fairing.  Pressure was stated to be 150 atmospheres (2,250 lbs./cu. in.).
  S.B.T. Fitted.
  Multi-unit Hydrophones Elag type.
  Echo Sounder Elag type.
  W/T Equipment Normal.  Mein and Radione III receivers carried.
  Rubber Dinghies Two large dinghies carried.
  Flotilla Twenty-ninth.
  Base Toulon.
  Badge Axe with "U.S.A." on blade.
  Field Post Number M. 09142.
  (i)  Departure from Toulon  
          "U 73" was scheduled to sail from Toulon towards the end of November, 1943, but was prevented from doing so by an aircraft attack on the base on 24th November.  A crane was knocked over by bomb blast and struck the U-Boat, injuring her slightly.  During the raid, the leading W/T rating was wounded and the U-Boat was forced to make her fifteenth patrol without him.  
          U 73" sailed at midnight, 3rd December, 1943.  She was escorted by several small patrol craft which remained with her for about one hour.  The U-Boat proceeded directly to her operational area off Oran and Algiers.  On passage she remained submerged continually except to charge batteries, usually between about 2000 and midnight, and to ventilate, for about 30 minutes before dawn each day.  


  (ii)  Attack on a Corvette  
          On the sixth day at sea, while patrolling off Oran, "U 73" sighted two corvettes.  A spread of three F.A.T-T.3's was fired but all failed to hit.  A T.5 was then fired from Tube II, forward, and struck one of the corvettes.  The prisoners believed that she was sunk.  (N.I.D. Note.  There is no record of such an attack taking place.)  
  (iii)  Flooded Torpedo  
          It was probably after this event, while servicing the torpedoes, it was discovered that one of the T.5's in the tube had leaked and become flooded with sea water.  The torpedo was dislodged with some difficulty.  
  (iv)  Sighting of a Destroyer  
          On 12th December, while proceeding submerged, screw noises were reported by the hydrophone operator.  The U-Boat came to periscope depth and sighted a destroyer, distant about 1,000 m.  (1,093 yards), bearing Green 96.  Prisoners believed that the destroyer sighted their periscope.  She dropped depth-charges in what was described as a haphazard manner.  They thought that the destroyer was attempting to frighten the U-Boat away rather then sink her.  
          (N.I.D. Note.  This incident cannot be identified in Admiralty.)  
  (v)  Collision with another Vessel  
          On 13th December, while "U 73" was proceeding by day at periscope, she collided with a vessel.  Some prisoners stated that the vessel was a destroyer, while others believed her to have been a small patrol boat.  Heavy seas were running and the U-Boat was driven upwards by a wave.  The vessel came down heavily on "U 73," leaving what prisoners took to be her Asdic dome behind.  The U-Boat's 20 mm. quadruple mounting was badly bent and rendered useless as a result of this encounter.  (N.I.D. Note.  This incident cannot be identified in Admiralty.)  
  (vi)  Off Algiers on 16th December  
          Early on 16th December, "U 73" was patrolling off Algiers.  At about 0800, an Italian cruiser was sighted leaving the harbour and heading for Spain.  Prisoners believed that a military commission of 60 men of the Badoglio regime were on board.  Although "U 73" was at action stations, as the cruiser was 3,000 m. (3,281 yards) distant and proceeding at a speed of 45 knots (sic) Deckert felt that it was useless to attempt an attack.  (N.I.D. Note.  The Italian cruiser, "Pompeo Magno, "3,362 tons, sailed from Algiers on the morning of 16th December.)  
          At 0830, a British submarine was making for Algiers.  
  (vii)  Attack on a Convoy  
          At about 1530 on 16th December, "U 73" sighted a convoy and closed to attack.  A T.5 torpedo was fired from Tube II and, according to the prisoners, hit a destroyer.  The prisoners were astonished to see the entire convoy come to a full stop at the time of the attack.  The U-Boat then fired a spread of three T.3 torpedoes from Tubes I, III and IV.  It was stated that one of these scored a hit on an 8,000-ton merchant vessel, one hit a corvette, and the third, its rudder jammed, circled around and above the U-Boat herself, causing considerable consternation among the crew.  The prisoners believed that the merchantman had been sunk and the corvette damaged.  (N.I.D. Note.  S.S." J.S. Copley," 7,176 tons, was torpedoed by a U-Boat on 16th December, 1943, in position 35° 54' N., 00° 53' W.  A tug was dispatched to her aid and she was towed into harbour, reaching Oran on 17th December.  There is no record of an escort ship being damaged.)  
          After making this attack, "U 73" submerged to a depth of about 40 m. (131.2 ft.).  
  (i)  Depth-Charge Attack  
          About three hours after attacking the convoy.  "U 73" was proceeding submerged when she was taken completely by surprise by a destroyer.  Some prisoners were violent in their criticism of Deckert, saying that he had been careless about maintenance, with the result that the rudders and motors were too noisy.  Others blamed him for proceeding at too shallow a depth.  
          The destroyer dropped a pattern of depth-charges which exploded below the U-Boat, inflicting considerable damage.  There was water entry forward between the bow torpedo tubes.  A sea inlet valve of the Diesel cooling system was fractured causing water to flow into the motor room.  "U 73" lost trim and sank to a depth that was variously estimated to have been between 160 and 230 m. (524.8 and 754.6 ft.).  
  (C51977)                                                                                                                       B**  


  (ii)  Gunfire Attack  
          Deckert ordered all tanks blown and, with the aid of one main motor, "U 73" broke surface at about 1900.  No enemy ship was visible and full speed ahead on the Diesels was ordered.  Suddenly searchlights from surface craft illuminated the U-Boat and she was immediately engaged by gunfire.  A number of hits were scored on the bridge and several of her crew were killed.  
          The order to abandon ship was given and shortly thereafter, the U-Boat sank.  One prisoners stated that "U 73" was not scuttled but was shipping so much water through rents in her pressure hull that she sank twenty minutes after being shelled.  No signal was sent to Control regarding the sinking.  
          (N.I.D. Note.  On the afternoon of 16th December, 1943, U.S.S. "Wolsey" was proceeding with U.S.S. "Edison" and U.S.S. "Trippe."  At 1815, "Wolsey" obtained asdic contact on a submerged U-Boat and made a depth-charge attack.  The U-Boat was forced to the surface.  The destroyer regained contact with radar and "Wolsey" and "Trippe" opened fire.  The U-Boat sank at 1935 in position 36° 09' N., 00° 50' W.)  
  (i)  U-Boat Escort in the Mediterranean  
          It was stated that the normal escort for U-Boats leaving or entering Mediterranean bases consisted of three or four small patrol boats with five-man crews.  These boats are fitted with German Asdic and flak armament.  They remain with the U-Boats only a short time, escorting them through the mine fields and the net and boom defences.  
  (ii)  New W/T Signal Procedure  
          A new system of recognition signals was instituted for Mediterranean U-Boats on about 1st January, 1944.  It is known as "Henno" and had already been given to "U 73" on her last patrol.  All U-Boat signals in the Mediterranean have prefix groups (Leitnummer) which run from 501 to 600.  There is one wavelength for night and another for day communication.  Wavelengths are changed infrequently because there is so little traffic between the U-Boats and Control.  
  (iii)  Anti-Aircraft Gunnery  
          A prisoner spoke of having heard of a new type of 20 mm. (0.79 in.) anti-aircraft ammunition, known as mine ammunition (Minemunition).  He stated that C.-in-C. U-Boats claimed that a single hit scored on an aircraft had sufficient explosive power to bring it down.  He considers this as typical of a series of exaggerated claims made by C.-in-C., U-Boats.  
          Another prisoner had taken a four weeks' course in anti-aircraft gunnery at Swinemünde.  After completing the course, he was awarded the flak specialists' badge.  Sixty men attended the course and each fired 800 rounds of 20 mm. and 60 rounds of 37 mm. (1.45 in.) ammunition.  
  (iv)  Use of D/F and Radione Sets  
          The order forbidding the use of D/F sets and aerials in the Mediterranean is no longer enforced.  Surfaced U-Boats are now permitted to use them as well as Radione Sets II, III and IV.  
(v)  Reception of Broadcasts
          It was stated that "U 73" listened whenever possible to W/T programmes broadcast at 0100, 0800, 1100, 1500, 1800 and 2100.  The long wave station at Toulon could be received when the U-Boat was submerged to periscope depth.  Signals from the Goliath station could be received at a maximum depth of 19 m. (62.2 ft.).  
  (vi)  Charging Batteries  
          U-Boat batteries should never be allowed to discharge beyond 1,500 ampere hours.  The maximum allowable acid temperature if 50° C. (122° F.)  
  (vii)  Dual Purpose Propulsion Units  
          A prisoner stated that trials with under water Diesel engines were being conducted in the Mediterranean.  (N.I.D. Note.  Extensible exhaust and inlet trunks for attachment to U-Boat diesels were reported at Toulon in January, 1944 (B.2).  See also C.B. 04051(94) (vi).)  


  (viii)  German Asdic  
          A W/T rating from "U 135" had taken a month's course in German Asdic (S-Gerät) in the summer of 1940.  He then served as Asdic operator in minesweepers of the 19th M/S Flotilla.  All minesweepers, he said are fitted with Asdic but as far as he knew, "U 43" is the only U-Boat to carry it.  All 500-ton U-Boats have Asdic wells which are, however, used for stores, rotary converters and latterly, for part of the radar.  The prisoner stated that he had seen a secret order forbidding the use of Asdic in U-Boats because of the ease with which it can be D/Fd.  
          The Asdic has a cathode ray oscillograph presentation.  A spot sweeps across the tube at one of two speeds - "fast" or "slow."  When doing a general sweep it is normally kept at "fast."  If a contact is obtained, the spot traverses an ellipsoidal path.  The traversing is then switched over to "slow" and again an ellipsoidal trace is obtained.  A knob at the side of the set is then turned until the ellipse becomes a straight line.  The setting on the knob is then read off and compared with tables which give the range of the object contacted.  Bearing can be obtained with great accuracy.  The prisoner believed that the bearing of mines could be estimated within one or two degrees.  He was uncertain of the maximum effective range, but thought it to be 500 m. (1,640 ft.).  The oscillator most commonly used was about 20 cm. (7.8 in.) in diameter and had a magnetic coil.  
          Other information was obtained from an Able Seaman who had served in "U.J.2104" and who had taken an eight weeks' course in German Asdic in 1942.  He had been awarded the Iron Cross, second class, for his skill.  
          (N.I.D. Note.  "U.J.2104," formerly H.M.S. "Kos," was sunk off Crete and subsequently raised and commissioned as an A/S vessel by the Germans.  She was in service for about two years as such and, after an action with H.M.S. "Sirius," was abandoned at Stampalia on 18th September, 1943.  (See No. S.O. (L) Levant's Aegean Report:  Aeg. R. 2/1043, 30th October, 1943.) .)  
          This prisoner gave a description of the gear used in U.J. Boats.  A rotary converter fed by the ship's 110 volt D.C. supplies at 220 volt A.C. current for the whole equipment.  This is stepped up to a high voltage, perhaps as high as 1,000 volts.  The receiver contains a cathode ray tube and a tilting mirror (Kippspiegel), the latter being partially silvered and semi-transparent.  The extensible dome is operated by hand and, when fully lowered, protrudes 90 cm. (35.4 in.) below the ship's keel.  The prisoner knew of two types of domes:  one containing four oscillators which was used in surface vessels, and one with eight oscillators for use in U-Boats.  In the first type, the same oscillators serve for transmitting and receiving.  In the second type, one set of four oscillators transmits and the second set of four, receives.  The transmitter frequency was said to be 15 k/cs. and is produced by an A.E.G. generator about 4 ft. high.  The generator contains two large valves, type A.S. 1,000.  
          Between the generator and the oscillator are a G.H. gear and I.K. gear.  The prisoner stated that these letter had no meaning but were merely used as a means of identification.  He did not know the purpose of the G.H. gear.  The transmitting-receiving switch was in the I.K. gear.  The impulses received by the oscillators pass through a special amplifier which is supplied by a separate power pack containing a "Stabilovolt."  From the amplifier, the impulses pass through the I.K. gear to the cathode ray tube and tilting mirror.  
          The tilting mirror is about 5 by 22 cm. (1.9 by 8.6 in.) and pivots around the short axis.  The prisoner thought that it made a revolution every 15 to 25 seconds.  Another prisoner felt that 5 seconds was more likely.  
          The trace in the cathode ray oscillograph is observed on the tilting mirror.  A luminous spot appears and enlarges to a horizontal line when a contact is obtained.  The line can be brought to the vertical and, from its form, the general nature of the target can be determined.  A U-Boat gives a very sharp thin line; a land echo will cause the line to bend slightly to one side; a wreck will give a line with indistinct edges.  Range can be read on a scale behind the semi-transparent tilting mirror.  The scale is in hectometres.  
  (ix)  K.D.B. Search Gear  
          The prisoner from "U.J.2104" stated that in A/S vessels, the K.D.B. search gear consists of six crystal units about 10 cm. (3.9 in.) in diameter, mounted in a single row on a retractable mounting about 90 cm. (35.4 in.) in length.  The extensible gear is trained to receive the maximum sound effect in earphones.  Bearing can be obtained within 5°.  The gear is easily damaged and, at high speed, the rushing of water makes reception very poor (see C.B. 04051(49) ).  Among associated gear, a special converter supplies a six valve amplifier.  The valves were a special type, about 2 in. high.  
  (x)  German A/S Tactics  
          When U.J. Boats are on patrol, a definite sector is swept continuously by the Asdic operator.  When a contact is obtained, the range and bearing are reported to the bridge and the course is altered accordingly.  Changes of bearing are reported every third turn of the tilting mirror.  If the bearing remains the same, only range is reported.  At close range (1,000 yards or less), the Commanding Officer orders slow speed and the K.D.B. search gear is used for confirmation and additional information on the nature of the contact.  When this operation is completed, full speed is ordered and, in the case of a submarine, the attack begins.  During the attack, no plot or recorder are employed, reliance being placed on the range and bearing reports of the Asdic operator.  


          (N.I.D. Note.  See also C.B. 04051(91) page 7, for information on "Naxos" and "Wanz" G.S.R.s given by prisoners from "U 340.")  
  (i)  General Attitude toward G.S.R.  
          Prisoners from "U 73" and "U 593" gave considerable information on G.S.R. types and procedure.  At the time these U-Boats were sunk (December, 1943), G.S.R. policy was greatly influenced by the belief that the radiation of sets enabled U-Boats to be located.  The chief criterion, in the judgment of the prisoners, was whether a set radiated or not.  
  (ii)  Wanze II  
          This set covered a waveband of 120 to 180 cm.  It is connected with either a drum type aerial of a figure-eight on the back of a radar aerial.  It has cathode ray tube and headphone presentation.  
          This type G.S.R. is replacing the Wanze I.  It is contained in the same housing as Wanze I which it completely fills.  There are believed to be 18 valves, mostly types R.V. 12 P.2000 and R.V. 12 P.2001.  It was stationed that the aerial input circuit is valveless, thus preventing the set from radiating.  Due to its lack of radiation, it can be switched on continuously.  Variable speed automatic search is provided in addition to hand search.  
  (iii)  Borkum  
          The waveband covered by Borkum G.S.R. is 30 to 300 cm.  It is connected with the drum type aerial and has a loud speaker presentation.  
          The set consists of 2 by 6 turn inductances wound on long formers connected by a condenser and a metal rectifier (See Plate).  This is connected to the drum type aerial and to the Radione set.  The I.F. stage valve, type ECH 11, is removed from the latter.  Contacts are transmitted on the loudspeaker of the Radione.  In the event of its being out of order, a strong contact can be heard on headphones connected directly across the Borkum.  
          The set does not radiate and was regarded as a stop gap until Wanze II could be installed.  Even after the installation, however, Borkum was still carried by "U 73."  
  (iv)  Naxos  
          The Naxos covers a waveband of 8 to 12 cm.  (N.I.D. Note.  It probably covers a much wider band in both directions with progressively diminishing sensitivity.)  A specially designed aerial is connected with the set, contacts being presented on a loud speaker.  
          A new pattern of this set was installed in "U 73."  It consisted of three parts:  a power pack, an amplifier unit and a small box ("X") about 10 cm. (3.9 in.) in size and of unknown content.  These parts are said to be connected as illustrated (see Plate).  The power pack and amplifier unit which together are called "Naxos" have a four-wire connection.  The number of wires in the other connections is unknown.  The Radione only has the I.F. stage valve removed, since this also cuts out the H.F. stage, the heater of which is wired in series with it.  
          The naxos aerial, roughly illustrated on the Plate, is fitted at an angle of 45 to a rotatable support, fixed to the periscope housing.  It was stated that the strongest signals are obtained when the "acorn" is pointing at an angle of 90° to the source of radiation.  The "Acorn" is of metal and can be unscrewed from the insulating cover to which it is secured.  The main tube, although referred to as copper, is of copper alloy.  In the top half of the tube is an oscillating circuit and in a projection on the lower half, an iron-selenium rectifier unit.  This is held in position by a spring to which is attached the screened cable which passes through the conning-tower hatch to the set.  A slot is cut in the bottom of the tube.  A reinforcing band is soldered round the top of this slot and through it a thumb screw with a knurled head passes.  This screw seems to hold an iron strip whose position is further adjusted by a second thumb screw passing through the slot.  Contact between the iron strip and the rectifier unit is made by means of a knife edge.  
  (v)  G.S.R. Procedure  
        When a U-Boat is surfaced, continuous watch is kept on Wanze II and Naxos.  The Wanze is kept on automatic search but in the Mediterranean, almost continuous radar contacts are obtained from shore-based stations on a wavelength of 141 to 143 cm.  As a result, little attention is paid to the Wanze.
          Normally, when a contact is obtained, the operator immediately notifies the Commanding Officer reporting with which set it was received.  If it was obtained on the Wanze, the operator switches to hand search to find the wavelength.  He then disconnects the drum type aerial from the Wanze and connects it to the Borkum.  If the contact is obtained on the Borkum, the aerial is once more disconnected to make sure that noise from the loud speaker is not a Naxos contact which, meanwhile, has supervened.  All contacts are logged with fullest possible details.  
          If, as in the case of "U 593," Borkum is not carried, the figure-eight aerial may be connected to the Wanze.  One prisoner stated that a rough bearing of plus or minus 25° could be obtained and was regarded as useful.  

Note:  the notation at lower left of the plate reads 8434 WT 57028/PK.4513.500.3.44

          When Naxos watch is kept, it is the duty of the bridge watch to rotate the aerial.  This was said to have been rather haphazardly done and no advantage of its directional properties was taken.  
          Confidence in G.S.R. appear to have been somewhat restored by the belief that Wanz II does not radiate.  There appears to be a tendency on the part of Mediterranean U-Boats, however, to disregard contacts, since they are so frequent.  
  (vi)  General Remarks on Radar  
          After a period in which Radar in U-Boats had fallen into disfavor, interest in it appears to have revived somewhat.  Prisoners believed that A/C type sets are being fitted in U-Boats.  
          To avoid confusion due to the phonetic similarity between the former German name for radar, "Fu.M.G.", and for G.S.R., "Fu.M.B.", the official designation for radar had been changed to "Fu.M.O."  
  (vii)  Seetakt Type Hohentwiel Radar  
          A telegraphist from "U 73" had attended a fourteen-day course at Le-Coq-sur-Mer (Den Hahn) on Radar and the following account of Seetakt type Hohentwiel Radar is derived largely from his statements.  A slight amount of information was added by a P.O. telegraphist from the destroyer, "T 25."  
          The Seetakt type Hohentwiel is a modification of a German Air Force A.S.V. Radar set.  (N.I.D. Note.  Believed to be Fu.G.200.)  It is known as operating on a 50 cm. wavelength, although the wavelength is actually 50.3 cm. and is said to be variable from 40 to 60 cm.  Frequency was stated to be 600 m/cs. and P.R.F. only 50 per second.  
          The aerial for use in U-Boats is the mattress type and rotatable through 180 either to port or to starboard.  It consists of six vertical transmitter dipoles above and six receiving dipoles below.  The reflector measures 90 by 120 cm. and is 25 cm. from the dipoles.  Prisoner added that the polar diagram of radiation shows a main forward beam and one small lobe on either side with axis pointing slightly backwards (N.I.D. Note.  The latter statements are considered untrue.)  
          The set consists of four parts:  the transmitter-receiver, the viewing section, the control section and the power pack.  Presentation is on a tube about 3 to 4 in. in diameter.  Pulse frequency is thyratron controlled.  An artificial target, consisting of a crystal controlled oscillator, is included in the set for calibrating purposes.  All valves are aircraft type.  
          In trials carried out in the Baltic, an E-Boat was detected at 12 km. (7.4 miles), a 4,000-ton ship at 20 km. (12.4 miles) and a large squadron of aircraft at 150 km.  (93.2 miles).  (N.I.D. Note.  These ranges are larger than would be expected.)  
  (i)  Relations between Italians and Germans  
          After an air-raid on Spezia in May, 1943, the tension between German sailors and Italian civilians was very great.  The Germans did not dare to leave the shelters for fear of being pelted with stones.  
(ii)  Sabotage in Southern France
          On 25th November, 1943, one of the prisoners from "U 73" was traveling by express train from Muhlhausen to Toulon.  A goods train on the opposite track was wrecked by explosive charges laid by French saboteurs.  The charges were placed at a point where the two trains were accustomed to pass one another.  The passenger train was undamaged but was delayed two hours by the incident.  
          Another prisoner stated that in Marseilles a large part of the city near the harbour was declared out of bounds for Germans.  On several occasions, members of the Gestapo had gone into these districts and had never returned.  Once a train near Marseilles had been blown up by saboteurs.  It is now the custom to send a locomotive hauling a coach filled with Frenchmen over the line from time to time, to test it for safety.  


  (i)  Early History  
          None of the prisoners from "U 73," with the exception of her C.O. had served in the U-Boat prior to her entrance into the Mediterranean.  It was not possible, therefore, to learn anything of her early history from the prisoners.   
          From other sources it is known that "U 73" was built by the Vulkan Yard, Vegesack, and that under command of Kapitänleutnant Helmut Rosenbaun she had completed her trials by late November or early December, 1940.  Her first patrol was probably off Ireland and it ended at Lorient which she reached late in December.  In April 1941, "U 73" was one of a group of U-Boats that attacked Convoy SC. 26.  Ten ships were sunk by the group then operating.  By the summer of 1941, she had changed her base from Lorient to St. Nazaire.  On about 31st July, 1941, she sailed from St. Nazaire on what was probably her fifth patrol, returning to port about 9th September.  
  (ii)  Sixth Patrol  
          On her sixth patrol, "U 73" entered the Mediterranean.  She sailed from St. Nazaire the end of September, 1941, passing through the Strait of Gibraltar about 1st October.  The patrol ended at Spezia.  In that base, she underwent extensive repairs and her Diesels were overhauled.  
  (iii)  Seventh Patrol  
          The U-Boat sailed from Spezia on her seventh patrol about 11th March, 1942.  After being at sea for about ten days, while proceeding at a depth of 40 m. (131 ft.) she was attacked by an aircraft.  Depth-charges were dropped, one of which exploded close to the bow torpedo hatch.  The pressure hull was badly buckled but it was not ruptured by the attack.  The U-Boat lost trim and Rosenbaum himself took over the controls.  "U 73" was forced to put in at Messina for two days and then proceeded to Spezia, reaching her base about 27th March.  
  (iv)  Eighth Patrol  
          The eighth patrol was Rosenbaum's last in command of "U 73" and on it he achieved his most spectacular success.  The U-Boat sailed from Spezia on 5th August, 1942, with instructions to attack U.S. shipping off the coast of North Africa.  On 11th August, H.M.S. "Eagle" was sighted, sailing in convoy with other warships and many transports.  "U 73" attacked from close range, firing a spread of four torpedoes with 15 m. (49 ft.) interval between each one.  The gyro angle setting was 1°.  All four scored hits on the aircraft carried which sank rapidly.  The U-Boat then took evading action as destroyers from the convoy hunted her.  She reached Spezia on 4th September.  At the end of this patrol, Rosenbaum left "U 73" and Deckert assumed command.  
  (v)  Ninth Patrol  
          On the ninth patrol "U 73" experienced much trouble from aircraft and was forced to submerged continuously.  She sailed from Spezia under her new commanding officer towards the end of October, 1942.  One prisoner, whose memory was rather vague, stated that a 26,000-ton ship was sunk with four torpedoes.  After the attack a U-Boat surfaced near "U 73" and thinking that she was a British submarine, Deckert beat a hasty retreat.  The patrol was said to have lasted 19 days and to have ended at Spezia during the second half of November.  
  (vi)  Tenth Patrol  
          On 30th November, 1942, the U-Boat left Spezia on her tenth patrol.  At about 2045 on 5th December she was attacked by aircraft and some damage was sustained, forcing her back to port.  She reached Spezia on 9th December.  (N.I.D. Note.  Aircraft "A" of 179 Squadron attacked a U-Boat 18 miles North-west of Cape Tenes at 2106 on 5th December, 1942.  It was thought that the U-Boat had been damaged.  
  (vii)  Eleventh Patrol  
        On about 23rd December, 1942, "U 73" began her eleventh patrol.  Prisoners stated that at least one and possibly two ships were sunk.  One was described as a merchantman of 8,000 tons loaded with munitions.  When she was hit by a torpedo she blew up with an enormous explosion.  Bits of debris were later found lodged on the bridge of the U-Boat, among them being an axe-head with "U.S.A." inscribed on the blade.  At the suggestion of one of the C.P.O.s this was adopted as the badge of "U 73."  The U-Boat returned to Spezia on 13th January, 1943, and remained in port for several months undergoing complete overhaul.
  (viii)  Twelfth Patrol  
          Early in May, 1943, following a lengthy overhaul at Spezia, "U 73" began her engine-trials, prior to going on patrol.  During the course of these, an explosion in the Diesel crank case occurred, injuring a number of the engine-room ratings.  After the damage had been repaired the trials were resumed and a second explosion occurred.  Several of the prisoners suspected sabotage in connection with these incidents.  
          It was not until the end of May or beginning of June, 1943, that the U-Boat was finally able to sail from Spezia on her twelfth patrol.  One prisoner claimed the sinking of a 4,000-ton freighter in the Western Mediterranean.  The patrol ended at Toulon about 25th June, 1943.  "U 73" remained in port for over a month while her 88 mm. (3.46 in.) deck gun was removed, the second bandstand added and the 20 mm (0.79 in.) quadruple mounted.  
  (ix)  Thirteenth Patrol  
          "U 73" sailed from Toulon on her thirteenth patrol on 8th August, 1943.  On 11th August, the anniversary of the sinking of "Eagle," it was stated that the U-Boat sighted a U.S. cruiser of the "Portland class off the coast of Italy.  In spite of the fact that two destroyers were escorting her, the U-Boat attacked the cruiser, scoring two hits.  Prisoners stated that breaking-up noises could be heard in the U-Boat and they were convinced that the cruiser had been sunk.  (N.I.D. Note.  There is no record of such an attack taking place.)  According to one prisoner, after this incident eight German army officers were taken off the coast of North Africa and transported to Toulon.  The patrol ended about 20th August.  


  (x)  Fourteenth Patrol  
          Late in September, 1943, "U 73" sailed from Toulon on her penultimate patrol, carrying with her a French civilian, said to be a Corsican.  En route to North Africa, this passenger was accommodated in the P.O.s' quarters.  The U-Boat proceeded to a point north of Oran.  At 2000, date unspecified, she altered course to 185° and at 0500 on the following day sighted a cape.  She approached the cape until she was about four miles off shore and then waited until dawn.  At break of day "U 73" submerged to periscope depth and approached to within 2 1/2 miles of shore.  She then submerged deeper and lay on the bottom for the rest of the day, in about 25 fathoms of water.  After dark the U-Boat surfaced once more and proceeded slowly towards land with her motors.  A few trusted members of the crew prepared a rubber dinghy for the Corsican.  It was loaded with various types of gear, including a hatchet, explosives and fuses.  The Corsican was clad only in swimming trunks in which his money had been sewn.  He was armed with a new pistol of very superior design.  When the U-Boat was about 400 yards off shore and with about 12 ft. of water under her keel, she hove to.  The Corsican sang a few snatches of "Deutschland über Alles," his only German words, launched his dinghy and made for shore.  The prisoners stated that he had been back and forth six times between France and North Africa.  (N.I.D. Note.  An agent was captured on 11th October, 1943, in the vicinity of Cape Khamis, and a powerful wireless set which he had hidden was found.  When interrogated he stated that he had been landed by "U 73" on the morning of 10th October, having sailed from Toulon early on 5th October.  
          After this incident, the U-Boat proceeded with her patrol.  Prisoners said that two merchant ships were sunk, one of 8,000 and one of 3,000 tons.  (N.I.D. Note.  There is record of only one attack made by a U-Boat on merchant shipping in the Western Mediterranean at this time.  On 1st October, 1943, S.S. "Stanmore," 4,970 tons, sailing in Convoy KNS. 27 was torpedoed and damaged in position 36° 41' N., 01° 10' E.  She was able to make port.)  "U 73" returned to Toulon on 28th October.  


(i)  Survivors:
English Equivalent.
Deckert, Horst Oberleutnant zur See Sub-Lieutenant
Altmann, Hans Leutnant zur See Junior Sub-Lieutenant
Kinkele, Kurt Leutnant zur See Junior Sub-Lieutenant
3.  6.22
Fenkner, Dr. Max Oberassistenzarzt Surgeon Lieutenant
Lepke, Fritz Obermaschinist Chief Stoker and Chief E.R.A., 1st or 2nd Class.
Schuck, Karl Obersteuermann C.P.O. (Navigation
4.  1.17
Brommert, Kurt Oberbootsmannsmaat Acting P.O. (Seaman's Branch)
Schnidt, Günther Bootsmannsmaat Leading Seaman
20.  1.20
Benthin, Werner Bootsmannsmaat Leading Seaman
13.  5.20
Lusch, Walter Maschinenmaat Leading Stoker and E.R.A., 5th Class.
15.  4.18
Haskamp, Clemens Maschinenmaat Leading Stoker and E.R.A., 5th Class.
23.  7.20
Mehlich, Walter Maschinenmaat Leading Stoker and E.R.A., 5th Class.
11.  7.21
Rachel, Gerhard Funkmaat Leading Telegraphist
2.  7.20
Zwietasch, Willy Mechanikersmaat Leading Seaman (S.T.)
4.  8.20
Wehling, Kurt Matrosenobergefreiter Able Seaman
24.  5.23
Klose, Curt Matrosenobergefreiter Able Seaman
24.  5.23
Waldmann, Heinrich Matrosenobergefreiter Able Seaman
23.  1.23
Prehn, Otto Matrosenobergefreiter Able Seaman
4.  2.23
Glück, Erich Matrosenobergefreiter Able Seaman
19.  2.24
Pohl, Gerhard Maschinenobergefreiter Stoker, 1st Class
25.  2.22
Kloss, Herbert Maschinenobergefreiter Stoker, 1st Class
20.  8.21
Kloos, Herbert Maschinenobergefreiter Stoker, 1st Class
17.  3.21
Staeger, Joseph Funkobergefreiter Telegraphist
14.  2.23
Braune, Erich Matrosengefreiter Able Seaman
2.  8.23
Morawietz, Wilhelm Matrosengefreiter Able Seaman
9.  1.23
Ziegner, Heinrich Matrosengefreiter Able Seaman
Hartling, Heinz Maschinengefreiter Stoker, 1st Class
21.  9.24
Essmann, Theodor Funkegefreiter Telegraphist
18.  6.24
Blasche, Kurt Funkegefreiter Telegraphist
Feist, Erhard Mechanikergefreiter Able Seaman (S.T.)
8.  5.24
Kirscht, Erich Mechanikergefreiter Able Seaman (S.T.)
Götz, Manfred Matrose I Ordinary Seaman
25.  9.25
Putz, Willy Matrose I Ordinary Seaman
22.  2.25
Nissen, Ude Matrose I Ordinary Seaman
Officers . .
Chief and Petty Officers . .
Men . .
  (ii)  Casualties:  
English Equivalent.
Moller, Wilhelm Oberleutnant (Ing.) Sub-Lieutenant (E)
Schmidt, Erich Obermaschinist Chief Stoker and Chief E.R.A., 1st or 2nd Class.
Ruf, Hans Obermaschinenmaat Acting Stoker P.O. and E.R.A., 4th Class
Bruggemann, Alfred Maschinenmaat Leading Stoker and E.R.A., 5th Class
Baum, Maschinenmaat Leading Stoker and E.R.A., 5th Class
Wegener, Helmuth Matrosenobergefreiter Able Seaman
Chwoika, Maschinenobergefreiter Stoker, 1st Class
Freudenthal, Maschinenobergefreiter Stoker, 1st Class
Stader, Fritz Maschinenobergefreiter Stoker, 1st Class
Glamm, Erwin Maschinenobergefreiter Stoker, 1st Class
Scheibe, Maschinenobergefreiter Stoker, 1st Class
Scheffler, Maschinenobergefreiter Stoker, 1st Class
Neu, Alfred Maschinenobergefreiter Stoker, 1st Class
Flemming, Matrose I Ordinary Seaman
Heyer, Matrose I Ordinary Seaman
Roepke, Matrose I Ordinary Seaman
Officers . .
Chief and Petty Officers . .
Men . .
  (iii)  Total Crew:  
Officers . .
Chief and Petty Officers . .
Men . .
(C51977)   500    4/44



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