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HMS Graph

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HMS Graph in 1943
HMS Graph in 1943
History
Kriegsmarine JackGermany
NameU-570
BuilderBlohm & Voss, Hamburg
Laid down21 May 1940
Launched15 April 1941
Commissioned15 May 1941
Capturedby the Royal Navy, 27 August 1941
History
Royal Navy EnsignUK
NameHMS Graph
NamesakeGraph (mathematics)
Acquired27 August 1941
Commissioned19 September 1941
DecommissionedFebruary 1944
FateRan aground 20 March 1944
General characteristics
Class and typeType VII C
Displacementlist error: <br /> list (help)
769 long tons (781 t) surfaced
871 long tons (885 t) submerged
Length67.1 m (220 ft 2 in)
Beam6.2 m (20 ft 4 in)
Draught4.74 m (15 ft 7 in)
PropulsionDiesel-electric
Speedlist error: <br /> list (help)
17.7 knots (20.4 mph; 32.8 km/h) surfaced
7.6 knots (8.7 mph; 14.1 km/h) submerged
Range15,170 km (8,190 nmi)
Test depth230 m (750 ft)
Armamentlist error: <br /> list (help)
• 1 × C35 88 mm/L45 deck gun with 220 rounds
• 5 × 21 in (533 mm) torpedo tubes (4 bow, 1 stern)
Service record
Part of:

list error: <br /> list (help)
Kriegsmarine:
3. Unterseebootsflottille (Training)

3. Unterseebootsflottille (Front Boat)

Royal Navy

Commanders: list error: <br /> list (help)
Kptlt. Hans-Joachim Rahmlow
Lt. George Colvin
Lt. Edward Dudley Norman
Lt. Peter Barnsley Marriott
Lt. David Swanston
Victories: None

German submarine U-570 was a Type VIIC submarine of the Kriegsmarine that was captured and commissioned into the Royal Navy as HMS Graph (pennant number P715). She was the only German U-boat to be taken into Allied service and to see active service with both sides in World War II.

Kriegsmarine Service

U-570 was laid down by Blohm & Voss at Hamburg in May 1940 and commissioned on 15 May 1941. After a series of short testing and commissioning trips in the Baltic, she moved to Norway where she carried out short training voyages and fired practice torpedoes. By 25 July, she had moved to the German U-boat base at Lofjord,[1] part of Asenfjorden, around 13 km north of Trondheim.

In late-August 1941, B-Dienst - the German naval codebreaking organisation - became aware of a large concentration of Allied merchant ships in the region of the North Atlantic south of Iceland. Admiral Karl Dönitz ordered 16 U-boats to the area.[2] The U-570 was to be one of these and, on the morning of 24 August, she put to sea on her first war patrol. Her planned mission was to patrol the area south of Iceland before proceeding to the U-boat base at La Pallice, France. She carried provisions for four weeks at sea.[3]

The submarine was commanded by Kapitänleutnant Hans-Joachim Rahmlow. He was an experienced naval officer, but had only recently transferred to U-boats, having previously been a gunnery and coastal defences specialist.[4] He had commanded the training submarine U-58 but had carried out no war patrols. Likewise, the First Watch Officer (second-in-command) had only served a few months with the U-boat branch, after serving on destroyers and the Second Watch Officer had little experience, having only recently been commissioned. The engineer was the only officer (and one of only four on-board) who had served on a U-boat war patrol. While the boat's petty officers had several years of navy service, many of the enlisted crew were still new to the German navy and had only a few months of U-boat training.[4]

The U-570's inexperienced crew was not unusual for the time. British interrogation of rescued crew-members of the U-501—sunk on her first patrol in September 1941—revealed that only seven out of 48 had previously seen a war patrol.[5]

Capture

On 27 August, U-570 spent much of the morning submerged. She had been four days at sea and this was to give respite to a crew that was suffering acutely from seasickness (several had been incapacitated). She surfaced at position 62°15′N 18°35′W / 62.250°N 18.583°W / 62.250; -18.583 at around 10:50 am, and was immediately detected by the radar of a nearby RAF Lockheed Hudson bomber of 269 Squadron operating from Kaldaðarnes, Iceland.[6]

Rahmlow, who had climbed out onto the bridge, heard the approaching Hudson's engines and ordered a crash-dive. But the aircraft reached the submarine before she fully submerged and dropped four 250-pound (110 kg) depth charges—one detonated just 10 yards (10 m) from the boat.[7]

The U-boat quickly resurfaced and around 10 of the crew emerged. The Hudson opened fire on them with machine guns, but ceased when the U-boat crew displayed a white sheet. An account of what happened was subsequently given to British naval intelligence interrogators by the captured crew members—the depth charge explosions had almost rolled the boat over, knocked out all electrical power, smashed instruments, caused water leaks and contaminated the air on the boat. The inexperienced crew believed the contamination to be chlorine, caused by acid from leaking battery cells mixing with sea-water, and the engine-compartment crew panicked and fled forward to escape the gas. Restoring electrical power—for the underwater electric motors and for lighting—would have been straightforward, yet there was nobody remaining in the engine compartment to do this.[8] The submarine was dead in the water and in darkness. Rahmlow believed the chlorine would make it fatal to stay submerged so he resurfaced. The sea was too rough for the crew to man their anti-aircraft gun so they displayed a white flag to forestall another, probably fatal, depth charge attack from the Hudson—they were unaware the aircraft had dropped all its depth-charges.

Most of the crew remained on the deck of the submarine as the Hudson circled above them. A radio request for help saw it being joined by another Hudson and a PBY Catalina flying boat of 209 Squadron, with a full load of depth-charges.[8] The German crew radioed their situation to the German naval high-command, destroyed their radio, smashed their Enigma machine and dumped its parts overboard along with the boat's secret papers.[9] Admiral Dönitz later noted in his war diary that he ordered U-boats in the area to go to U-570's assistance after receiving this report[10] and the U-82 responded, but was prevented from reaching the U-570 by Allied air patrols.[8]

The U-570 with one of the Royal Navy trawlers, photographed from an RAF Catalina

The U-570's transmission was in plain language and it was intercepted by the British. Admiral Percy Noble, commander of Western Approaches Command, immediately ordered a small armada of ships to race to the scene.[8] By early afternoon, fuel levels had forced the Hudsons to return to their base in Iceland. The Catalina, a very long-range aircraft, was ordered to watch the submarine until Allied ships arrived. If none came before sunset, the aircraft was to warn the U-570's crew to take to the water, then sink her.[11] The arrival of the first vessel—the anti-submarine trawler HMT Northern Chief—averted this. The Catalina returned to Iceland after flying in circles over the U-boat for 13 hours.[12]

The German crew remained on board U-570 overnight; they made no attempt to scuttle their boat as Northern Chief had signalled she would open fire and not rescue survivors from the water if they did this. During the night, four more naval trawlers and the destroyers HMS Burwell and HMCS Niagara reached the scene. At daybreak, there was a series of Signal lamp messages between the Allies and Germans, with the Germans repeatedly requesting to be taken off as they were unable to stay afloat, and the British refusing to evacuate them until they secured the submarine and stopped it from sinking—the British were concerned that the Germans would deliberately leave behind them a sinking U-boat if they were evacuated. The situation became more confused when a small float-plane (a Northrop N-3PB of 330 Squadron) appeared. Unaware of the surrender, it attacked the U-570 with small bombs and fired on the Northern Chief (which returned fire).[13] No damage was done and Burwell ordered the aircraft away by radio.

The weather worsened; several attempts to attach a tow-line to the U-boat were unsuccessful. Believing the Germans were being obstructive, Burwell's captain ordered warning shots to be fired with a machine gun, but some of the German crew were accidentally hit and wounded. With much difficulty, a small party of British sailors got on board the submarine to attach a tow-line and the Germans were taken off. The ships began slowly sailing to Iceland with the U-570 and with a relay of Hudsons and Catalinas constantly patrolling overhead. They arriving at dawn on 29 August at Þorlákshöfn, There, the submarine was beached as she had been taking on water and was thought to be in danger of sinking.

Salvage and Repair

Two days after the submarine's arrival, a British submarine commander—Lieutenant George Colvin—together with a team of engineering warrant officers and civilian technical experts arrived at Þorlákshöfn from Britain to carry out the U-570's initial examination and salvage.

The submarine was then lying broadside on to the surf and listing heavily to starboard (i.e. inshore). She was on a gently shelving beach of very soft sand, completely open to the south-east, and had been driven well up the beach by a moderate swell. The interior of the submarine was unlit and was in a chaotic state; leaks of oil and water from the broken gauge glasses of internal tanks had combined with vast quantities of provisions, flour, dried peas and beans, soft fruit, clothes, bedding, and the remains of scores of loaves of black bread to form a revolting morass that in places was knee-deep. It was subsequently discovered that in this ship the crew's W.C. had been converted into a food locker and overturned buckets of excrement added to the general noisome conditions.

— Lieutenant GR Colvin, RN, Ex-German Submarine "U 570" - Report of Proceedings (3rd October, 1941)[14]

Colvin's team was able to restore lighting and buoyancy; U-570 was re-floated and towed around the coast to the British naval base at Hvalfjörður where repairs were made that would enable her to make the trip to Britain under her own power.[14]

The British discovered that the depth charge damage to the U-boat was not critical—there were leaks in some of the ballast tanks and a small leak in a fuel tank. Around one third of the battery cells were cracked and the bow had been buckled. Water had leaked in through a valve that had been unseated by the explosions and through glass gauges that had broken; other damage was minor and no evidence of chlorine gas found. In his report, Colvin stated his opinion that there was no evidence of any damage control being carried out and that an experienced submarine crew would have been easily able to improvise repairs, stay submerged and likely evade the air-attack.[15] After their surrender, the German crew had attempted to destroy instruments and fittings, but, with the exception of the wrecked radio and the damaged torpedo firing computer, the attempt appeared half-hearted and the damage was not significant. Also, useful papers had missed destruction. Copies of encrypted signals and their corresponding, plain-language, German texts were found—material of use to the British code breaking effort.[16]

U-570 spent three weeks at Hvalfjörður, being repaired and taking short sea trials to test the engines and steering. On 23 September, she was carefully inspected by US Navy officers who had been dispatched to Iceland for that purpose;[17] one of the submarine's G7a torpedoes was removed and handed over to the Americans.[18] An eye-witness recalls that at one point, a Hudson bomber flew low over U-570, signalling with a Morse lamp, "This ****** is mine."[19]

On 29 September, the submarine set out for the UK, manned by a Royal Navy Prize crew under the command of Lieutenant Colvin.[20] Escorted by the destroyer HMS Saladin, she sailed on the surface as her diving planes had been damaged by the beaching at Þorlákshöfn.[17] Her arrival at Barrow-in-Furness on 3 October was filmed by Pathé News newsreel cameras,[21] and reported in the press.[20] The capture would later be featured in British propaganda.[22] The capture of several other U-boats, such as the U-110 (which had sunk whilst under tow) was kept secret to conceal the seizure of their code-books and Enigma machines. U-570's situation had been reported to the German high command. Also, so many ships, aircraft and personnel had been involved in her capture that any attempt at secrecy would have been futile.

She was placed in a dry-dock in the Vickers shipyard in Barrow. Her repair was complicated by depth-charge damage to her bow—her plating had been buckled, trapping four, electrically-powered G7e torpedoes in their torpedo tubes. Two officers from the Royal Navy's Department of Torpedoes and Mines Investigations had the task of retrieving them for examination. The dock was evacuated while a volunteer shipyard worker cut the armed torpedoes free with an oxyacetylene cutter under the officers' supervision. One of the officers—Lt Martin Johnson—then removed the Magnetic pistols (detonators) from the torpedoes and made them safe—a dangerous task as the pistols were sensitive mechanisms and quite large enough to produce a lethal explosion. For this act, he was awarded the George Medal on 8 December 1942.[23][24]

One of the Kriegsmarine flags of the U-570 was presented to the Hudson bomber pilot—Squadron Leader James Thompson—and is now part of the collection of the RAF Museum. Thompson and his navigator/bomb-aimer—Flying Officer John Coleman—were also awarded the Distinguished Flying Cross on 23 September 1941.[25]

German Response

Initially, all the German naval high command knew of U-570's situation was her radio message, saying she was under air-attack and unable to submerge; they only learned of her capture from later British press reports. They were concerned for the security of their communications and Vice Admiral Eric Maertens, head of navy communications, was ordered to report on this. He concluded that in the worst case scenario—that is, the British had secured U-570's codebooks and Rahmlow had revealed to them his secret keyword—communications would be compromised until a new list of Enigma machine settings came into force in November. However, he believed this worst case to be unlikely and that the U-570's crew would have almost certainly destroyed their secret material. Even if they had not, the additional security of the commander's memorised, secret keyword would defeat British cryptanalysis.[26]

In fact, the British code-breakers at Bletchley Park found the extra security of the keyword procedure to be simply of "nuisance value".[27] The U-570's crew had indeed destroyed their Enigma machine and code-books but the British, assisted by the earlier capture of the U-110 had been breaking German naval cyphers since June 1941 and would not be seriously impeded until February 1942, when a new naval Enigma cypher would remain unbroken for ten months—the so-called "Shark Blackout".

Apart from Rahmlow, the captured officers were taken to an officers' PoW camp at Grizedale Hall in Cumbria.[28] There, Rahmlow (in absentia) and his second-in-command, Berhnard Berndt, were found "guilty of cowardice" by a "Court of Honour" convened by other German prisoners, including U-boat ace Otto Kretschmer. On the night of 18/19 October, Berndt escaped from the camp. However, he was soon apprehended by a detachment of Home Guard and was shot when he tried to escape.[16]

According to some sources, he had escaped from the camp with the stated intention of redeeming himself by making his way to the U-570's dockyard at Barrow (a distance of only 22 miles) and somehow destroying her.[16][28] Another source states he was forced to make an escape attempt by a group of senior German prisoners, who enforced a brutal regime of punishing those who held anti-Nazi views or who co-operated with the British, and that Berndt only broke away and ran from the Home Guard when he realized they were returning him to Grizedale Hall; they shot him dead after he ignored warning shots.[29]

Royal Navy Service

The disposition of the boat was initially uncertain. Winston Churchill was favour of handing her over to the Americans for repair, both for propaganda and as a means of deepening then-neutral America's engagement in the Battle of the Atlantic.[30] The Americans were eager to have her, but the Royal Navy objected. She was commissioned into the Royal Navy as HMS Graph on 19 September 1941, and assigned the Royal Navy pennant number N46. She was given a name beginning with a 'G' to signify German, i.e., denoting that Graph was a captured vessel. The name Graph was also chosen owing to the extensive testing carried out on her (and therefore the many "Graphs" drawn up).[28]

Trials

Once seaworthy, meticuous trials were conducted to measure every aspect of Graph's sailing and diving characteristics. Her safe diving depth was discovered to be 230 metres (750 ft)—much deeper than the British thought for this kind of boat. At the time, Royal Navy depth charges had a maximum depth setting of 170 metres (560 ft) so the Germans could dive out if their reach. Depth charges were soon modified to take account of this.[31] The boat's acoustic and magnetic characteristics were examined by different Admiralty research establishments.[32][33] Models, based on her, were used in experiments with underwater explosions,[34] apparently to test depth-charge effectiveness.

The Allied techical experts found much to praise about her design and construction. Graph's auxiliary machinery was on rubber mountings, to quieten the boat by reducing sound transmission into the hull.[35] The quality of her construction was excellent. Her underwater acoustic equipment was found to be a sophisticated array of Hydrophones that was significantly better than the British equivalents,[30] and several design features were recommended to be copied in British and American submarines. The main criticism of the boat was poor and cramped crew accommodation, which would degrade crew performance on long patrols.

In a highly secret project, Graph was also used a model for the construction of three, full-sized, mock-ups of the control compartment, wardroom and radio room of a Type VII U-boat. These were used to train specialist groups of sailors, who would form boarding parties whenever a damaged U-boat was blown to the surface. They were trained to operate a U-boat's ballast-tank valves, to reverse any scuttling attempts by the crew, and were taught where to quickly search for cryptographic equipment and documents.[28][36]

Active Service

On 21 October 1942, in the Bay Of Biscay, about 50 nautical miles (90 km) north-north-east of Cape Ortegal (44°31′N 7°25′W / 44.517°N 7.417°W / 44.517; -7.417), Graph encountered the U-333. Four torpedoes were fired but all missed.[37] In December 1942, HMS Graph sighted the German cruiser Admiral Hipper on her return to Altenfjord following the Battle of the Barents Sea, but Hipper was travelling too fast to be attacked. Three hours later, Graph sighted one German destroyer towing a second, and attacked. However, her torpedoes missed.

Decommissioning

Defects, exacerbated by a shortage of spare parts, led to her being placed in reserve, and she was decommissioned from active service in February 1944. On 24 March 1944, she was being towed by HMS Allegiance from Aberdeen to the Clyde for scrapping when she ran aground near Coul Point (55°47′53″N 6°29′14″W / 55.79806°N 6.48722°W / 55.79806; -6.48722), on the west coast of Islay, Scotland and abandoned. She was partially salvaged and scrapped in 1947. In 1966, the salvage diver Keith Jessop removed some more of the wreck, but stopped work when he became involved in a court case over salvage rights.[38] Some remains of HMS Graph remained visible at low tide on the rocks near Saligo beach at least into the 1970s, with the pressure casing of the conning tower and periscope tube clearly visible (the cladding and railings etc all washed off in the Atlantic storms many years before).

See also

References

  1. ^ CB 4051, page 4
  2. ^ Blair, page 340
  3. ^ CB 4051, page 5
  4. ^ a b CB 4051, page 2
  5. ^ Blair, page 362
  6. ^ Thomas, Andrew (May 24, 2001). "Icelandic Hunters - No 269 Squadron Royal Air Force" (PDF). Aviation News. St Leonards-on-Sea, East Sussex,: HPC Publishing. Retrieved 2009-09-13.{{cite journal}}: CS1 maint: extra punctuation (link)
  7. ^ CB 4051, page 6
  8. ^ a b c d Blair, page 342
  9. ^ CB 4051, page 7
  10. ^ Sebag-Montefiore page 161
  11. ^ "AIR 41/47—The RAF in Maritime War - The Atlantic and Home Waters: Vol III The Preparative Phase July 1941 - Feb 1943.". Air Historical Branch: Narratives and Monographs, in The National Archives. 1954.
  12. ^ Blair, page 345
  13. ^ Blair, page 344
  14. ^ a b CB4318, Appendix 1, page 50
  15. ^ CB4318, Appendix 1, page 52
  16. ^ a b c Sebag-Montefiore page 162
  17. ^ a b "Report On The German Submarine U-570 Class Captured By The British in August 1941". United States Navy, reproduced by uboatarchive.net. 28 September 1941. Retrieved 14 September 2009.
  18. ^ CB4318, Appendix 1, page 51
  19. ^ "The Whole Truth". WW2 People's War. BBC. 1 November 2005. Retrieved 14 September 2009.
  20. ^ a b "Captured U-Boat in Port—British Crew Bring Home Aircraft's Prize". News. The Times. No. 49048. London. col C, p. 4. template uses deprecated parameter(s) (help)
  21. ^ His Majesty's U-Boat (Motion picture). London: British Pathé. 1941-10-09. 1133.07. Retrieved 2009-09-13.
  22. ^ "A Grã-Bretanha Defensora da Liberdade [Great Britain, Defender of Liberty]" (Poster). Imperial War Museum: Posters of Conflict. Visual Arts Data Services. Retrieved 2009-09-25.
  23. ^ "Lt-Cdr Martin Johnson". The Times. 2004-07-28.
  24. ^ "No. 35815". The London Gazette (invalid |supp= (help)). 1942-12-04.
  25. ^ "No. 35283". The London Gazette. 1941-09-23.
  26. ^ Sebag-Montefiore page 163
  27. ^ Sebag-Montefiore page 164
  28. ^ a b c d Blair, page 347.
  29. ^ Burt, Kendal; Leasor, James (2006). "Chapter 4". The One That Got Away. Pen & Sword Military. ISBN 1844154378.
  30. ^ a b Blair, page 346.
  31. ^ Macintrie, Donnald (2004). U-Boat Killer: Fighting the U-Boats in the Battle of the Atlantic. Rigel Publications. ISBN 1898799784.
  32. ^ "ADM 259/575—Trials of captured U-boat HMS/M Graph". Royal Navy, now in The National Archives. 1942.
  33. ^ "ADM253/436—Magnetic field of captured German submarine U570 (HMS/M Graph)". Mine Design Department and Mining Establishment, Royal Navy, now in The National Archives. 1941.
  34. ^ "ADM 281/156—Underwater explosion experiments with models of ex-German submarine Graph ex U570 ASSET trials". Admiralty: Naval Construction Department, now in The National Archives.
  35. ^ Bud, Robert; Gummett, Philip (2002). Cold War, Hot Science: Applied Research in Britain's Defence Laboratories, 1945-1990. NMSI Trading Ltd. p. 166. ISBN 1900747472.
  36. ^ "ADM 1/11826—NAVAL TRAINING (54): Control room of U570 (later HMS/M GRAPH): construction by Vickers-Armstrong for training boarding parties". Royal Navy, now in The National Archives.
  37. ^ Blair, Clay (1999). Hitler's U-Boat War: The Hunted 1942-45. Weidenfeld & Nicolson. p. 68. ISBN 0297840770.
  38. ^ Jessop, Kieth; Hanson, Neil (2001). Goldfinder. John Wiley and Sons. p. 99. ISBN 047140733X.

Bibliography

  • Weisse Flagge, 1956 article from German magazine Kristall. Translated by Gerry Raffé, 269 Squadron RAF Website. Includes an account of Berhnard Berndt's prison camp escape and Rahmlow's own description of the circumstances of the boat's surrender.
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