Additions and Corrections to "U boat Tankers 1941-45"

2 Sept 2006

Some new information has became available, predominantly from German sources, and readers have pointed out a few corrections. By and large, the accuracy of the book remains very high, so far as is known.


"The German Ciphers are Broken".

Page 26. 'The Admiralty belatedly stopped to ask themselves...'
The Admiralty had intended to leave two surface tankers alone, to lull German suspicions, but both were discovered through chance by British warships in mid-ocean!
Pages 27-33. The account in Chapter 3 is over-skimpy. As well as using Enigma to encipher their codes, the Germans also used a "short signals" book, whereby many common messages could be reduced to groups of four letters, short-lists for the numbers of individual U boats and an "address book" to encipher U boat rendezvous positions from 1942. None of these codes was ever broken directly; decryption rested entirely on the seizure of the relevant short-code books from captured U boats (including from U 505, whose capture was casually dismissed on page 210 of the book). The Germans proved to be remarkably reluctant to change these short-codes once issued, so that captured data remained in force for 1-3 years before a new capture became necessary. The use of commander's names to describe the U boats from mid-1941 (and hence to disguise their types, which might have been obvious from the U boat numbers) that they commanded never fooled British Intelligence for long, and was not even applied consistently by U boat Command, who often resorted to U-numbers when addressing boats at sea. Times to decrypt U boat transmissions varied through the war, but were typically 1-3 days. Thus rendezvous information was often deciphered in time for the Allies to anticipate the rendezvous.
Page 49. "Early successes boosted ... by U 459 and U 116."
Early indications were that these cows had only added about seven-ten days extra patrol time, with corresponding few extra sinkings, to the boats that had been refuelled. [Author's additional note:] This crude assessment failed to compensate for the fact that some boats were refuelled for their return home, so naturally no additional benefit arose, and that the main constraint at this time, when targets were easily found, was shortage of torpedoes.

"The Milk Cows"

Page 64. U tanker trim.
U boat Command transmitted the following order to boats at sea on 15 March 1943:
"To maintain proper trim in the U boat tanker, all boats on being supplied are to take from the tanker the quantities of victuals appropriate to the fuel allocation. Intend to fit out U boat tankers accordingly."

"The Problems Mount"

Page 112. Ramming of U 119, 2 March 1943.
The destroyer that rammed U 119 has been identified by Commodore Jan Drent (Canada) as HMCS Assiniboine. The destroyer had located U 119 with 10cm radar, not detected by the U boat's 150cm radar receiver. She inflicted only a glancing blow on the turning minelayer before dropping six shallow-set depthcharges whose explosions knocked out the destroyer's electrical equipment. Repairs to Assiniboine took four months.

"Black May".

Page 128. Air attack on U 459.
Two bombers attacked U 459 as she crossed the Bay of Biscay. The first was a Whitley bomber that never returned to base. Her last message was "engine trouble", presumably as a result of the return fire from the U tanker. The second was a Liberator bomber that attacked through intense, accurate flak, dropping six depthcharges on the first run and three depthcharges on the second. A third attack was made with machine guns only. The Liberator sustained only slight damage before returning to base.
Page 132. Fido. A spy in the USA reported to U boat Command in 1944 that an American plant was manufacturing acoustic homing torpedoes. The account was not believed for the extraordinary "reasoning" that, if homing torpedoes were being used by the Allies, there could be no survivors, and it was known that survivors were being taken from some sinking U boats. The possibility that homing torpedoes might be in use at the same time as other anti-submarine weapons was beyond the imagination of U boat Command.

"Disaster in the Bay".

Page 148. Post-war friendship of Stiebler and pilot of Sunderland.
The pilot (Dudley Marrows) dropped his single rubber dinghy for the aid of U boat survivors in the water. When he returned to base, the pilot was severely censured for jeopardising his only means of escape should he be shot down over the Bay of Biscay.

"Disaster in the Atlantic".

Page 152. "Disappointing results from U-minelaying".
U boat Command considered that the mines must be defective or wrongly placed, owing to the poor results obtained (actually due to decryption alerting the minesweepers).
Page 154. "H/F D/F. The Germans had guessed..."
U boat Command knew that the Allies had built many shore-based direction-finding stations all around the North and South Atlantic. It seemed reasonable to suppose that together these stations could provide a highly accurate fix on any transmitting U boat.
Page 155-6. Air attack on U 487.
(Additions by Herrn Pötter and Vorstadt, of U 487.) The bridge watch had observed a wooden box floating ahead of the tanker. Metz gave the order to bring all available empty sacks onto deck in order to fill them with a strange type of cotton wool (actually gun-cotton!). This was despite the standing order of BdU, that no floating flotsam should become fished out, since it could bring about the loss of the U-boat by distraction of the watch. This order proved to be prophetic.
At about 14:30h U-487 was unexpectedly shot at by American fighter-aircraft, causing the sacks loaded with gun-cotton to flash into balls of fire all over the deck. The main rudder was badly damaged by a bomb so that the boat was no longer maneuverable. The tanker was also no longer submersible with leaks.
The "Vierling" of U-487 was actually only a twin flak gun. Two additional dummy barrels had been fitted underneath, to deter attacking aircraft. One aircraft was shot down. When the ammunition finally failed to reach the twin-gun due to flooding below, Metz gave the command 'Abandon ship'. Metz remained absent-mindedly on the bridge, and failed to observe an aircraft closing with guns firing. He was hit by several bullets and fell dead.
Page 158. "U 489 managed to dive in heavy rain."
According to survivors' accounts, U 489 had been hunted all that night by destroyers. She was forced to resurface on the 4th in order to recharge her batteries and revitalise her air.

"Refuelling in Other Theatres".

Page 166/169. Light Cruiser "Eritrea".
This ship was actually little more than a motor yacht, armed with two gun turrets, designed for the use of an Italian ambassador. After escaping from Penang after the Italian surrender in September 1943 she arrived safely in Ceylon, where her crew was unable to furnish Allied interrogators with any useful data about German refuelling zones.
Page 171. The Penang Base.
It took about eight weeks to turn around U boats for sea after they had arrived. The surrounding waters were periodically mined by Allied submarines, but a major aerial minelaying effort by Liberators on 27 October 1944 - which might have been repeated at any time - caused Germans and Japanese to abandon Penang as a naval base in favour of Batavia.
Page 171. Sinking of UIT 22 (Wunderlich).
The rendezvous between UIT 22 and U 178 was set at a position 600 miles south of Cape Town. South African forces intercepted the signals and a Catalina (Wunderlich thought a Liberator) of the S.A.A.F. surprised UIT 22 on the surface at the rendezvous and dropped five depthcharges, causing the boat to submerge with a heavy list. A second Catalina again caught UIT 22 on the surface (after she had signalled her condition to U boat Command) and dropped depthcharges, resulting in the disappearance of the submarine in a huge oil slick. On the following day, U 178 arrived at the rendezvous to find the oil, patrolling aircraft and no survivors.
Page 174. Japanese use of UIT boats.
UIT 24 and UIT 25 were used in the traffic between Japan and the oil terminal in Borneo.
Page 175. Submarine blockade runners.
Five Japanese submarines attempted to carry cargoes from Penang to France and back again between mid 1942 and early 1944. Three completed the round trip, but two of these were sunk with their cargoes while onward-bound for Japan from Penang.
Page 215/218. U 195.
U 195 left Bordeaux with a 250-ton cargo comprising optical instruments, mercury, dismantled V weapons, torpedoes, blueprints, radar sets and a Japanese technical officer. After safe arrival in Batavia, the cargo was removed for trans-shipment to Japan. U 195 left Tanjong Priok on 17 January 1945 for the homeward run, but was forced to return with diesel trouble. She refuelled the returning U 532 (100 tons), before reaching Batavia on 3 March.

"Return to the North Atlantic".

Page 182. Leuthen Pack "shoot-out" policy.
The policy of surfaced Leuthen U boats shooting it out with attacking aircraft was ordered by Doenitz against his own better judgement, and on the advice of U boat commanders newly returned from sea. The order was soon rescinded.
Page 183. Leuthen Pack refuelled by U 460/Decryption.
The British Admiralty was so alarmed at the prospect of renewed wolfpack attacks in the north Atlantic that it asked the Americans to use their carrier groups to hunt down and sink U 460, whose position was known from decryption. The Americans were happy to oblige.
Page 193. Loss of U 220.
German historian Alex Niestlé has noted that the war diary of U 256 records that, 30 minutes after the air attack that supposedly sank U 220, U 256 and U 220 agreed by underwater signalling to make for a new rendezvous. Eight hours later, the surfaced U 256 observed a series of explosions on the horizon and U 220 failed to keep the revised rendezvous. There was no air attack recorded at this time. Thus the true story of the end of U 220 will probably never be known.
Page 193. "All attempts at refuelling in the North Atlantic...abandoned."
U boat Command had always been amazed that the Allies had never attempted to interfere with supply operations north of the Azores during 1942-1943, since they must have been apparent even if only from the volume of signal traffic. Thus, when US carrier groups started to sweep the areas with decryption information, U boat Command merely shrugged its shoulders and said "Well, that's that then. They finally got round to doing it." This anticipation of disaster helped to conceal the almost casual use by the US of U boat cipher decryptions.

"Maintaining the Pressure".

Page 202. Losses to the long-range Type IXB/IXC U boats had been so great in March-July 1943 that thereafter there were never enough to maintain more than four on patrol in remote theatres at one time. Inevitably, then, the strategy of sinking ships faster than they could be built had to give way to the "inferior" strategy (in Doenitz's eyes) of tying down enemy forces.
Page 209. Cancellation of the U tankers.
Work was abandoned on U 491-493 at Deutsche Werke in June 1944, when the boats were about 75% complete, and never resumed. Other Type XIV U tankers (U 494-500 and U 2201-2204) under construction or ordered at Germania Werft were suspended on 3 June and cancelled on 23 September.

"The End of the Milk Cows"

Page 215 "at this time...U 180 hit a mine..."
The historian Alex Niestlé has discovered that the escort left U 180 in deep water late on 23rd August 1944, so that a mine sinking is most unlikely. The most likely explanation [author's view] for the loss is a schnorchel defect (compare the troubles experienced by U 219 at the same time). Experiences from other U boats make it clear that a sufficiently serious schnorchel failure could pole-axe an entire crew within sixty seconds.


Page 229. Spanish Co-operation.
U 30 was refuelled by the "Max Albrecht" at El Ferrol in June 1940. U 68 had an exhaust valve repaired, and was also refuelled, by "Max Albrecht" (May 1942). U 66 had to visit "Max Albrecht" in September 1942 for refuelling, after a previous fuelling by U 460 had resulted in the inadvertent transfer of nine tons of water as well as sixteen of the intended 25 tons of oil. The error was only discovered later.
"Bibliography" - Addition.
Niestlé, A., German U boat Losses in World War II, Greenhill (1998).
"Bibliography" - Far-Eastern war diaries.
Page 239.
The German Naval Command ordered in April 1945 that all war diaries that could not safely be brought to Germany should be destroyed rather than risk capture. This applied especially to war diaries of U boats sent to the Far East. All were destroyed. Thus there are no original records for operations by U boats in the Far East.


"The Birth of the U tanker".

Page 19.
" was essential to sink as many Allied merchant ships as possible in the shortest possible time."

"The Supply Ships".

Page 24. Convoy HX126.
JD Brook has pointed out that this convoy still had a weak escort when overwhelmed by U boats.

"The German Ciphers are broken".

Page 26. Map 3-1.
Lotheringen => Lothringen.

"The Milk Cows".

Page 57. One cbm = one ton.
Carsten Wenke has pointed out that although this relationship is true for water, one cbm of fuel oil amounts to less than one ton.
Page 67. Typical late flak arrangements for U 462.
U 462 carries a single 20mm cannon.
Page 75.
'...fuelling areas north of the Azores...'

"Attack on Cape Town".

Page 102. "Cremer remained with the tanker".
Cremer returned as a passenger with U 333 to France.
Page 104. Brake sailed with U 907 as escort.
Frans Becker (Belgium) has pointed out that 'U 907' must have been a code word for the surface tanker Brake. The real U 907 had not yet been commissioned.
Page 104. City of Cairo (8,034 tons).

"The Problems Mount".

Page 109. Convoy TM.1.
This convoy was first sighted on 29th December 1942 by U-124. (JD Brook)

"Disaster in the Atlantic".

Page 158. U 489 sailed.
U 489 sailed on the same day that the ill-fated U 459 and U 117 had sailed from Bordeaux.
Page 159. A Mining Operation by U 117.
The minelaying operation was off, not of, Gibraltar.

"Refuelling in Other Theatres".

Page 169. "Second Monsun Group".
Three U boats were sent to the Indian Ocean in October/November 1943 as the "Second Monsun Group". Only one arrived. The book describes a group of three U-cruisers outward-bound to the Indian Ocean from Germany as the Second Monsun group (only one arrived), but I believe now that the title applies to the Type IXB/IXC boats U 510 (Kptlt Eick; arrived), U 172 (sunk) and U 850 (sunk). All sailed from Biscay ports. U 510 spent 155 days at sea, sank nine ships (winning her commander the Knight's Cross) and arrived at Penang on April 5th 1944. U 510 set back to Germany in 1945, but was forced to put into St. Nazaire (still German-occupied) in April 1945 owing to shortage of fuel (despite having been previously refuelled by the homeward-bound U 861 south-east of Madagascar). She was then taken out of service and subsequently was deployed by the post-war French Navy. U 861 reached Trondheim (Norway) with "the last drop of oil in her tanks".

"Return to the North Atlantic".

Page 197. Refuelling by U 219 of U 762.
U 762 (Hille) not U 530 was refuelled by U 343 on 5 November and not, as stated, by U 219. The mention of U 530 is a mistake.

"Maintaining the Pressure".

Pages 205-6. Refuellings by U 488 in March-April 1944.
Mr. Becker has pointed out inconsistencies in the text compared with his own database. The author has re-examined the BdU war diary and also decrypted U boat messages for the period 13 March to 9 May 1944. Key war diaries of U boats that attended the rendezvous have been lost, because the boats were sunk or headquarters at Penang later destroyed them (see "Omissions", above).
The decrypts show that the U boats involved were ordered to maintain W/T silence until commanded to report by U boat Command - thus signals from U boats are very scanty. Refuellings were to be carried out at night. The Germans appear to have reverted to the earlier procedure of making short changes to compromised rendezvous and U boats were directed to the general area before receiving final details. Disguised rendezvous positions were transmitted by U boat Command, but these must have been repeatedly betrayed by U boats giving their positions without disguise. All the U boat signals were decrypted within one-two days, giving the Allies plenty of time to react to rendezvous orders given up to a week in advance.
It appears that only four refuellings were made by U 488 in all:
U 843 (outward-bound, reported on 25 March that she had been refuelled)
U 123 (homeward-bound, 29 March, reported by U 488 on 30 March)
U 129 (outward-bound, 16/17 April, found in her war diary, but there were no signals)
U 537 (outward-bound, 16/17 April - circumstantial evidence only. U 537 was ordered to refuel at the same date as U 129, is known to have been in the area on time from a position signal, and survived to reach Penang. Subsequently U 537 was sunk. There is no signals evidence before 9 May for a refuelling with U 488.)
U 543 - outward-bound, survived and may have been refuelled (no signals). Later sunk on 2/7/44 in mid-Atlantic.
Page 207. U 188...ordered on 30 August.
This should read '30 April'.

"The End of the Milk Cows"

Page 215. U 219 finally left her bunker on 20 August.
U 180 and U 195 left Bordeaux on 22 August, and were followed next day by U 219. Owing to a shortage of suitable escorts, U 219 did not enter the Bay of Biscay until the 24th. The signal announcing the imminent departures of U 180, U 195 and U 219 was decrypted by British Intelligence.
Page 231. Appendix 3.
U 459 was sunk on 24 July 1943 (not 25th).


HMS Castleton was a Town-class destroyer (ex-American), not a frigate. The name has been wrongly spelled throughout as 'Castledown'.


U 1060 / U 1061 / U 1062.

The first two of these Type VIIF torpedo transports successfully operated a shuttle service between Kiel and the U boat base at Narvik, with intermediate stops at Kristiansand, Bergen, Trondheim and other ports, between December 1943 and July 1944. By then, each boat had completed four round-trips and had returned to Kiel. Both boats were now re-equipped, the schnorchel being the most important new item, and in October 1944 both were sent, separately, to Horten for schnorchel training. U 1060 subsequently moved north to Trondheim, where her subsequent destruction by air attack and grounding (28 October) has already been outlined. U 1061 was damaged by a bomber while en route to Bergen on 30 October. She returned in stages to Trondheim where repairs took until 29 January 1945. She put to sea again, but was forced to return to Bergen where she remained until 26 April. Now with a new commander (Jaeger), U 1061 moved southwards to Kristiansand with U 991 and U 1307, but, with the end of the war imminent, returned again to Bergen on 4 April where she surrendered.
U 1062 was escorted by the minesweeper M-403 when unsuccessfully attacked from the air on 22 December 1943 and not, as stated by British sources, by a destroyer.

U 218.

This sole surviving Type VIID U minelayer was also withdrawn from service for refit and schnorchel installation in German waters between October 1944 and March 1945.

U 234 - U 490.

These U boats entered service unexpectedly late. U 234 (type XB) was damaged by bombing while being built (May 1943). The entry of U 490 (type XIV; Oblt z.S. Gerlach) into service was delayed by two serious accidents. After being commissioned on 27 March 1943, she suffered a battery explosion during trials on 7 May, necessitating a return to Kiel for repairs and extra work. Released again on 23 June, U 490 conducted refuelling exercises with the 27th U boat Flotilla off Gotenhafen in July 1943. She had just surfaced after a practice dive on the 23rd when water poured into the diesel room, apparently through open vents, and the tanker sank to the bottom, 65 metres deep. After an anxious ¾ hour of repairs, U 490 managed to regain the surface, but the electric motors, radio communications and rudders had all failed (the signal to this effect, made through the accompanying U 845, was decrypted by British Intelligence). U 490 returned to dockyard hands from 29 July to 10 February 1944.
Training resumed with trials of a new schnorchel. Eight boats were given practice refuellings. Some eight months later than planned, U 490 was ready for operations on 4 May 1944. U 490 did use a schnorchel during her one war patrol, a fact unknown to U-boat Command that ordered her to France for refitting on 1 June 1944.
Another interesting facet of U 490 was that the tanker was strengthened by having her ribs fitted externally, rather than internally. These gave more room within, and enabled the tanker to dive safely to 300 metres. She also had a strong flak defence, comprising two twin 20-mm mounts on the upper gun platform, and an automatic 37-mm gun of the new design on the lower platform. There was additionally an automatic 37-mm deck gun forward of the conning tower; however U 490 lacked radar which was planned to be fitted at Bordeaux.

New Plans for U-tankers

Plans were made in the middle of 1943 to bring into rapid production the new 'electric' U boats of Type XXI, through a policy of mass assembly at the dockyards of the various prefabricated U boat sections. The scheme reduced the requirement for refuelling U boats since the Type XXI craft possessed their own large fuel supplies, while their unusual design meant that any deviation from the standard construction pattern would require considerable expenditure of labour. As a preliminary step, on 8 October 1943 all outstanding contracts for the remaining Type XIV U tankers were switched from Deutsche Werke Kiel (which was now required to produce 'electric' U boats) to Germania at Kiel, and the series U 491- U 500 was laid down.
By now, U tanker Types XV (2,500 tons) and XVI (5,000 tons) had been mooted as developments of the Type XIV, but incorporating large workshops. Both types would be seriously under-powered by their standard diesel engines (taken from the Type VIIC boat, and also used in Type XIV), and were promptly rejected by Doenitz. The 'K' team also proposed the Type XXB that combined elements of the XIV-series tanker and the XX-series U transporter into a general purpose U supplier that could transport either oil or rubber in external tanks. The battery size would be larger at the expense of some storage capacity internally and/or externally. This scheme was also rejected on 18 October 1943.
The 'K' team now proposed two schemes at a meeting with the Naval Staff on 8 November:
1. Type XIVB, a development of the standard U tanker with extra batteries in an extension under the pressure hull. It was agreed that this useful addition would be fitted to the last six U tankers to be completed by Germania in 1945.
2. A Type XXID modification of the standard attack 'electric' U boat, with all torpedo tubes and torpedoes removed, the upper deck widened to support fuel transfer, various trimming modifications, the fitting of oil transfer equipment and extra refrigeration added for food storage. An open bridge, for easy manoeuvring on the surface, and increased flak protection were also to be provided. A Type XXIC U transporter was also recommended, essentially lacking only the torpedo tubes of the attack version, but both the C and D subtypes would also lose half of their battery capacity to create more space.
Again the non-standard requirements of the new types caused difficulties and no construction was ever initiated. On 27 March 1944 Doenitz directed that the new 'electric' boats might take on fuel but only when submerged, so the changes to the bridge and flak of Type XXID could be dropped, while two torpedo tubes were reintroduced to provide some defensive capability. Again no work was started before the end of the war. The long-range attack boats always had clear priority of production, but were themselves repeatedly delayed by production difficulties.
All the Type XIV U tankers (U 494-500 and U 2201-2204) under construction or ordered at Germania Werft were suspended on 3 June 1944 and cancelled on 23 September.

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