Copy No. 49 of 49
	Op-16-Z
	NAVY DEPARTMENT
	OFFICE OF THE CHIEF OF NAVAL OPERATIONS
	WASHINGTON
	Final Report – G/Serial 42
	REPORT ON THE
	INTERROGATION OF SURVIVORS FROM U-490
	SUNK 12 JUNE 1944
	DISTRIBUTION:
	BAD
	BUORD
	BUSHIPS
	BUSHIPS (Code 515)
	BUSHIPS (Code 815)
	COMINCH (F-21)
	COMINCH (F-4253)
	COMINCH (F-45)
	COMINCH (FX-40)
	COMINCH (FX-43)
	COMNAVEU
	DNI (Ottawa)
	G-2 (Col. Sweet)
	Op-16-1 via Op-16-1-F
	Op-16-FA-4
	Op-16-P
	Op-16-W
	Op-20-G
	Op-23-C
	SONRD
	Lt. Cdr. V. R. Taylor
	C.O., Naval Unit, Tracy, Calif.
	Lt. J. I. Eiband (COMNAVNAW, CSDIC, AFHQ)
	Lt. S. R. Hatton (COMNAVNAW, CSDIC, AFHQ)
	Lt. J. T. Rugh, Jr. (JICA/ME)
	COMASDEVLANT
	CINCLANT
	COM8THFLEET
	COM4THFLEET
	4 September 1944

 

	TABLE OF CONTENTS
	PAGE CHAPTER I.   INTRODUCTION 1                 II.   DETAILS OF U-490 2                 III.   EARLY HISTORY OF U-490 12                 IV.   FIRST AND ONLY PATROL OF U-490 15                 V.   SINKING OF U-490 17                 VI.   GENERAL REMARKS ON U-BOATS 20                 VII.   CREW OF U-490 23                 VIII.   OTHER U-BOATS 26
ANNEX:  CREW LIST OF U-490 AND U.S. EQUIVALENTS OF GERMAN NAVAL RANKS

 

	CHAPTER I.  INTRODUCTION
	U-490, a 1600-ton supply U-boat commanded by Oberleutnant zur See der Reserve Wilhelm Gerlach, was sunk on 12 June 1944 in approximate position 42.23 N. – 39.56 W. by units of Task Group 225.  The U-boat was on her first patrol and had supplied no other boats when she was sunk.  The patrol was to have terminated in Bordeaux about mid August.
	The entire complement of U-490, 61 officers and men, survived.  Fearing that they would become British prisoners of war in Freetown, they signed a statement that they would answer all “honorable questions” upon assurance of being taken to America.  At the preliminary interrogation in Casablanca, this statement was of considerable aid to interrogating officers.  They proved to be less security conscious than most U-boat crews recently encountered.  Final interrogation was facilitated by several captured notebooks and other documents.
	U-490 was a standard supply U-boat manned by an undistinguished crew.  The chief point of interest is her construction.  Although she was designed as a normal Type XIV boat, the ribs were welded to the exterior rather that the interior of the pressure hull.  It was probably because of this structural feature that she was able to dive to a depth of 300 meters at the time of the final attack, without damage to herself.
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	CHAPTER II.  DETAILS OF U-490
	TONNAGE
	1600 tons.
	TYPE
	XIV.
	BUILDING YARD
	Deutsch Werke, Kiel.  Commissioned 27 March 1943.
	YARD NUMBER
	315.
	INSIGNIA
	Bee on a downward pointed sword; worn on the caps of the crew.
	FIELD POST NUMBER
	M-51045.
	FLOTILLA
	The flotilla was intended to have been the 12th at Bordeaux.
	COLOR
	Dark gray.
	CONSTRUCTION
	U-490 had the standard Type XIV internal layout.  She differed from previous boats of this type in that the ribs were welded to the exterior rather than to the interior of the pressure
	-2-

 

	hull.  The prisoners believed that this was done in order to facilitate construction, lend greater stability to the boat, give more room within the pressure hull, and allow greater diving depths.  The ribs were the normal T-shaped type and were spaced about 50 to 70-cm. apart.
	BRIDGE CONSTRUCTION
	Standard.  Two armored shelters were fitted, a three-man shelter to starboard and a one-man shelter to port.
	ARMAMENT
	(A)  Guns:
	Two twin 20-mm. mounts on Platform I.  One full automatic 37-mm. gun on Platform II.  One full automatic 37-mm. deck gun forward of the conning tower.  Four MGs. Type 15 on the bridge.
	(B)  Torpedoes:
	No torpedo tubes and no torpedoes carried.
	DIVING
	Crash diving time to periscope depth, 40 to 50 seconds.  The greatest depth attained was said to have been 300 meters.
	S.B.T. (Submarine Bubble Target)
	Fitted to the starboard side of the electric motor compartment.
	D.C.P. (Depth Charge Plotter)
	Not fitted.
	-3-

 

	PROPULSION
	(A)  Diesels:
	Two G.W. (Germania Werft), six-cylinder, 1400 H.P., 40-cm. Bore, 46-cm. Stroke.
	Telegraph Speeds R.P.M.       3 x AK (Extreme Emergency Speed) 500         AK (Full Speed) 470         GF (Crusing Speed) 410         2 x HF (3/4 Speed) 390         HF (Half Speed) 330         LF (Slow Speed) 260         KF (Dead Slow) 216
	It was stated that the speeds were originally 20 to 25 r.p.m. higher.  It was found that the Diesels were two light for such high speeds and that they would function more effectively with less r.p.m.
	(B)  Motor/Generators:
	Siemens.
	Telegraph Speeds R.P.M.       AK (Full Speed) 300         GF (Cruising Speed) 240         HF (Half Speed) 160         LF (Slow Speed) 115         KF (Dead Slow) 90-95
	- 4 -

 

	SUPERCHARGERS
	Rootes type (Kapsel).
	SCHNORCHEL
	Fitted to port side.  (For details, see Chapter VI.)
	SWITCHBOARDS
	Siemens.  Later replaced by switchboards of Voight and Haeffner design.  Said to be identical with those fitted in normal 500 ton U-boats.
	BATTERIES
	Afag.  Lead-acid type, 62 cells.  Stated to have been slightly larger than the normal U-boat battery.  Capacity, about 13,000 amp./hrs.
	COMPRESSORS
	One Junkers and one electric compressor.
	CLUTCHES
	Disk type, Lohmann-Stoktertoth.
	TANK CAPACITIES
	The tank capacities from aft to forward:
	Cubic Meters       Stern Buoyancy Tank 7.09         No. 1 Main Ballast Tank 32.35         No. 2 Main Ballast Tank 40.55         No. 1 Fuel Oil Tank 60.72
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	No. 2 Fuel Oil Tank 58.02         No. 3 Fuel Oil Tank 78.00         No. 3 Main Ballast Tank (emergency fuel) 88.16         No. 4 Main Ballast Tank (emergency fuel) 90.44         No. 5 Main Ballast Tank (emergency fuel) 71.28         Compensating Tank 59.00         Quick Diving Tank 15.88         No. 6 Main Ballast Tank 65.46         No. 7 Main Ballast Tank (emergency fuel) 87.38         No. 8 Main Ballast Tank (emergency tank) 69.40         No. 4 Fuel Oil Tank 72.40         No. 5 Fuel Oil Tank 53.00         No. 6 Fuel Oil Tank 40.00         No. 9 Main Ballast Tank 41.85         Bow Buoyancy Tank 30.26
	OIL CAPACITIES
	Capacity of external fuel oil tanks is 697.52 cubic meters.  The internal fuel oil tanks hold 29.60 cubic meters making a total fuel oil capacity of 727.12 cubic meters.  The lubricating oil capacity is 19 .52 cubic meters.
	GERMAN ASDIC
	Not carried.
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	RADAR
	Not carried.  It was stated that a Hohentwiel type set was to have been installed in Bordeaux after the first patrol.  A special converter and aerial were carried for this set.
	G.S.R. (German Search Receivers)
	Wanz G-2, Naxos and Borkum carried.  The Wanz was said to have covered a wave band of from 80 to 240-cm., the Naxos a wave length of about 10-cm.
	G.S.R. AERIALS
	Two fixed basket-type aerials carried, one on the bridge and one on the Schnorchel.  These were connected to the Borkum if necessary.  A Fliege type aerial was used with the Naxos.  Earphones were employed to listen to Naxos signals.  The Fliege dipole could be adjusted to any angle by bending it but the distance from dipole to reflector was always 41-mm.  Each time after it was adjusted, this distance was checked.
	ROTARY CONVERTERS
	One 6 KVA.
	One 1.5 KVA.
	One 0.3 KVA.
	One transmitter converter.
	One UT converter in the motor compartment.
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	U.K. GEAR (T.B.S.)
	Carried during the working-up trials only.
	U.T. (Underwater Telegraphy)
	Carried.
	RADIO EQUIPMENT
	(A)    Transmitters:
	One 200-watt Telefunken transmitter, 20-80 meter wave band.
	One 40-watt Lorenz emergency transmitter, 13-60 meter wave band.
	One 150-watt Telefunken transmitter, 300-600 meter wave band.
	(B)    Receivers:
	One short wave Telefunken receiver.
	One “Main” Telefunken receiver, T9K39.
	One all wave Elag 10/12 receiver fitted with a 20-watt Siemens amplifier for broadcasting throughout the boat over the public address system.
	NAVIGATIONAL AIDS
	(A)    Compasses:
	One Anschütz master gyro compass with four or five repeaters.
	One magnetic compass.
	(B)     Depth Gauges:
	One main graduated to 200 meters.
	One gage graduated to 25 meters.
	-8-

 

	One Papenberg gage for periscope depth.
	(C)    Echo Sounder:
	Elag type carried.
	(D)    Elektrolot:
	Elag type carried.
	(E)     Salinometer:
	An instrument for measuring the salt content of water was in the control room.  It was described as a graduated glass tube, about 12 inches in length and tapering toward the top.  It was weighted with lead shot and floated in a metal cylinder which had connection with the outside seawater.  Some prisoners believed that this instrument could indicate water temperature and density as well as salt content.
	INFRA RED EQUIPMENT
	None carried.
	H/P AIR BOTTLES
	Six banks of air bottles carried.  Their capacities varied from a 200 liter bottle for starting the Diesels, to bottles of 460 liters.  Air bottles could be charged submerged when the Schnorchel was used.  (For details, see Chapter VI.)
	OXYGEN BOTTLES
	Fifteen to twenty carried.
	-9-

 

	POTASH CARTRIDGES
	About 800 “type L” carried.
	R.D.B. (Radar Decoy Balloons)
	Carried.
	R.D.S. (Radar Decoy Spar Buoys)
	Not carried.
	WATER DISTILLER
	Manufactured eight to ten liters of fresh water per hour.
	AIR CONDITIONER
	Fitted.
	RUBBER DINGHIES
	A one-man dingy for each member of the ship’s company carried.  In addition, two large rubber dinghies were stowed between the deck and the pressure hull.
	MACHINE SHOP
	A well equipped machine shop was located in the stern compartment.  It contained the usual hand tools, power drills, lathes, etc.
	CARGO
	A large cargo of provisions and spare parts for other U-boats was carried but it was possible to obtain only sketchy details of its nature.  Thirty cases of radio equipment were carried.
	-10-

 

	These included four or five Wanz, two Naxos and two Borkum G.S.R. sets.  Two Fliege aerials and a number of Naxos crystals were carried.  Extra converters and transmitters were also carried.  The cargo also contained many machine parts, electrical equipment, and several cylinder heads.  It was stated that at least two tons of fresh fruit had been embarked in Kiel and that it had taken three days to load the provisions.  Perishable food was stowed in a special refrigerator room located below the floor plates immediately abaft the control room.
	-11-

 

	CHAPTER III.  EARLY HISTORY OF U-490
	COMMISSIONING
	U-490 was built at the Deutsche Werke, Kiel.  The engine room personnel were assigned to the boat in February 1943 to stand by new construction.  The boat was commissioned on 27 March 1943.
	FIRST SERIES OF TRIALS
	After the commissioning, U-490 remained in Kiel for about ten days for U.A.K. tests.  She then proceeded to Swinemünde for anti-aircraft gunnery practice.  This was followed by the usual engine and speed trials at Danzig.
	At Hela during the Agru-front, the first of a series of mishaps occurred.  On the evening of 9 May the boat was lying alongside a pier, and most of the crew was enjoying shore liberty.  The assistant engineer officer was supervising the charging of the batteries.  He neglected to open the exhaust lines and then resultant battery explosion wrecked several cells and otherwise damaged the battery compartment.  The Agru-front trials were broken off and U-490 returned to Kiel where the damage was repaired and new batteries were installed.  The U-boat remained in port for about a month during which a number of the ratings were drafted to other stations and replacements were made to the ship’s company.
	SECOND SERIES OF TRIALS
	Early in June, U-490 again proceeded to Swinemünde where gunnery practice was held for the benefit of the new members of the crew.  The Agru-front trials at Hela were then completed after which, underwater sound
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	tests were held off Rönne.
	U-490 next proceeded to Gotenhafen about mid July for the tactical exercises.  These consisted chiefly of navigational problems involving meeting other U-boats at specified times and positions for the purpose of supplying them with fuel oil.  After the second or third meeting another mishap occurred which resulted in serious damage to the U-boat.  On 23 July, during a practice dive, the main air induction valve was left open and a stream of water poured into the Diesel compartment with such force that it shot through the open door, completely flooding the motor compartment.  Prisoners estimated that 60 tons of water were shipped before the valve could be closed.  U-490 went down out of control and buried her stern in the muddy bottom.  She remained there for some time at an angle of 600 before the water-tight doors of the motor compartment could be closed.  Finally all tanks were blown and the U-boat slowly came to the surface but with almost no freeboard.  Some of the waterlogged gear was piled on deck to dry, the Diesels were started and U-490, looking very bizarre, began her inglorious return to Gotenhafen at slow speed.  One night, while under way, another U-boat sighted her and, due to her peculiar silhouette, took her for a Russian submarine.  U-490 fired recognition signals just in time to avoid being attacked.  The U-boat put in at Gotenhafen for emergency repairs and then proceeded to Kiel where she arrived on 29 July.  She went into drydock for extensive refit.
	This second period of overhaul lasted almost six months.  Due to the damage inflicted on factories by Allied aircraft, delivery of
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	machine parts and electrical equipment was extremely slow.  The electric motors of the U-boat were removed and repaired, Platform I was widened, armored shelters were built on the bridge, the mounting of the deck gun was strengthened, and Platform II was added.  No gun was installed on Platform II at this time, however.
	FINAL SERIES OF TRIALS
	Early in January 1944. U-490 sailed from Kiel to complete her trials.  She proceeded to Sonderborg where a second series of underwater sound tests was carried out.  She then went through an abbreviated course of tactical exercises.
	FINAL ADJUSTMENTS
	U-490 returned to Kiel the end of March 1944 for final adjustments.  A full automatic 37-mm. gun was installed on Platform II and the Schnorchel was installed.  A month later, she began to embark stores for her first patrol.  Many spare parts and a large amount of provisions were loaded.
	-14-

 

	CHAPTER IV.  FIRST AND ONLY PATROL OF U-490
	DEPARTURE
	U-490 sailed from Kiel at 0800 on 4 May 1944, accompanied by a 500-ton U-boat and escorted by a Sperrbrecher.  Due to the slow speed of the escort vessel, the passage to Kristiansand lasted until 6 May.  At Kristiansand, U-490 topped up with water, embarked beer and oranges and, the next morning, sailed.
	PASSAGE THROUGH THE ATLANTIC
	U-490 rounded the southern tip of Norway and then followed a course of about 3400 until 13 May when she reached approximate position 65.02 N. – 00.00.  She then proceeded on a westerly course until 18 May when she was in approximate position 65.03 N. – 07.00 W.  The U-boat then turned southwest, making good a course of about 2160.  This course was maintained throughout the remainder of the patrol.
	Until the final attack on 11 June, the patrol was uneventful.  The U-boat proceeded submerged at a depth of about 40 meters most of the time.  When weather permitted, batteries were charged submerged by using Schnorchel.  Otherwise, the U-boat surfaced only in bad weather to charge batteries and ventilate.  Only once during the patrol, radar transmissions were received on the G.S.R.  On 24 May when the U-boat was in 60.00 N. – 20.00 W., she signaled her position and a weather report to Commander-in-Chief U-boats.  On 6 June, news of the Allied invasion of France was received and on the following day the U-boat was ordered to continue her patrol.
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	Gerlach was extremely nervous during the patrol and maintained as strict a radio silence as possible.  Only rarely was the extensible aerial employed to receive news broadcasts while the U-boat was submerged.  Attempts were made to receive broadcasts while using the Schnorchel but reception was very poor.  On 11 June a brief signal was sent to Commander-in-Chief U-boats that was to result in the sinking of the U-boat.
	(O.N.I. Note: While searching for a U-boat known to be in the area, Task Group 225 D/F’d an enemy high frequency transmission at 0136 GCT on 11 June.  The transmission was fixed by Commander-in-Chief within 50 miles of a position 40 miles west of the Task Group.  Three ships of the group obtained accurate ground wave bearings and course was shaped to intercept.)
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	CHAPTER V.  SINKING OF U-490
	FIRST ATTACKS
	U-490 was proceeding at a depth of about 80 meters at 1100 German time on 11 June, when the crew was startled by explosions in the vicinity of the boat.  The Oberfunkmaat who was standing the hydrophone watch estimated that the explosions were from 300 to 500 meters away.  From the sound, he judged that the detonations were aircraft bombs.
	Immediately after the first attack, the U-boat dived to 240 meters and proceeded at silent running speed.  About 20 minutes later, a second series of explosions was heard very close to the U-boat.  These were believed to have been depth charges.  (O.N.I. Note: U.S.S. FROST gained a sonar contact, range 650 yards, at about 0745 GCT on 11 June.  At 0805, she fires a hedgehog pattern which resulted in three hedgehog detonations followed two minutes later by two muffled explosions.  U.S.S. HUSE was designated to assist.  HUSE and FROST both streamed FXR gear and proceeded to attack.  At 0821, HUSE fired a pattern of nine depth charges set to 350 to 450 feet.)
	SUBSEQUENT ATTACKS
	Series after series of depth charges fell near U-490 and her Engineer Officer ordered the boat to a depth of about 300 meters.  An attempt was made to employ the S.B.T. but the plunger jammed, rendering it useless.  The Oberfunkmaat who manned the hydrophones stated that he was unable to hear the usual sounds of depth charges striking the water
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	and sinking.  The first warning of their presence was the explosions themselves.  Usually the attack was preceded by the noise of asdic.