HMS Graph (pennant number P715) was a German Type VIIC U-boat captured and recommissioned by the British Royal Navy during World War II.
Commissioned as U-570 in Nazi Germany's Kriegsmarine in mid-1941, she was attacked and captured on her first patrol. She provided the Royal Navy and United States Navy with useful information about German submarines. Refitted for use by the Allies, she carried out three combat patrols with a Royal Navy crew, becoming the only U-boat to see active service with both sides during the war. She was withdrawn from service in 1944 due to problems maintaining her. While being towed to the breakers for scrapping, she ran aground on the Isle of Islay, off the west coast of Scotland. Some of the wreckage was removed as scrap but some remains to the present day.
Design and construction The submarine was built to the German Type VIIC design. She had a displacement of when surfaced, and when submerged. The boat was long, with a beam of , and a draught of . The diesel-electric propulsion system provided a maximum speed of surfaced or submerged. The U-570 had a fuel capacity of which gave a range of at .CB 4318 p. 4 The test depth of the submarine was .
Her main armament consisted of five 53.3-cm (21-inch) torpedo tubes; four in the bow, and a fifth in the stern. She could carry a total of 14 torpedoes – five in the torpedo tubes, seven reloads inside the pressure hull, and a further two in water-tight canisters outside the pressure hull. The boat was fitted with an 8.8-cm C/35 deck gun (with around 150 rounds of ammunition), and a 2-cm Flak 30 anti-aircraft gun with a 28-cm stereoscopic rangefinder.CB 4318 p. 26 She also carried several machine guns.CB 4318 p. 5
Blohm & Voss laid down U-570 at Hamburg on 21 May 1940. The submarine was launched on 20 March 1941.
Kriegsmarine service U-570 was commissioned into the Kriegsmarine 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,CB 4051, p. 4 part of Trondheimsfjord, around 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.Blair 1996, p. 340 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.CB 4051, p. 5
Kapitänleutnant Hans-Joachim Rahmlow commanded U-570. He was an experienced naval officer, but had only recently transferred to U-boats, having previously been a gunnery and coastal defence specialist.CB 4051, p. 2 He had commanded the training submarine , 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 crewmen) 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.
U-570s inexperienced crew was not unique for the time. British interrogation of rescued crew-members of —sunk on her first patrol in September 1941—revealed that 41 out of 48 crew were on their first war patrol.Blair 1996, p. 362
Capture
On 27 August 1941, 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). Earlier that morning, a Lockheed Hudson bomber of 269 Squadron, RAF, flown by Sergeant Mitchell and operating from Kaldaðarnes, Iceland, had attacked her. The attack failed when the Hudson's bomb-racks failed to release its depth charges. U-570 surfaced at position at around 10:50 am, immediately below a second 269 Squadron Hudson, flown by Squadron Leader James Thompson. Thompson was patrolling the area after Mitchell summoned him by radio. Rahmlow, who had climbed out onto the bridge, heard the approaching Hudson's engines and ordered a crash-dive. Thompson's aircraft reached U-570 before she was fully submerged and dropped its four depth charges—one detonated just from the boat.CB 4051, p. 6
U-570 quickly resurfaced and around 10 of the crew emerged. The Hudson fired on them with machine guns, but ceased when the U-boat crew displayed a white sheet. The captured crew members later recounted to British naval intelligence interrogators what had happened—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.Blair 1996, p. 342 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 Thompson circled above them, his aircraft now joined by a second Hudson that had been en route from Scotland to Iceland and had broken off its journey to lend assistance.The Imperial War Museum's collection includes a recorded interview of former RAF Flying Officer Hugh Eccles, who was one of the crew of this aircraft. A radio request for help saw a Consolidated Catalina flying boat of 209 SquadronThe aircraft was Catalina number AH553, flown by Flying Officer Edward Jewiss; see; Conyers Nesbit (2008), p.74. Jewiss had been partially responsible for sinking the two days earlier. See: Blair (1996), p.342.Conyers Nesbit 2008, p.74 being scrambled at Reykjavík; it reached the scene three hours later. 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.CB 4051, p. 7 Admiral Dönitz later noted in his war diary that he ordered U-boats in the area to go to U-570s assistance after receiving this report;Sebag-Montefiore p. 161 responded, but Allied air patrols prevented U-82 from reaching U-570.
U-570s transmission was in plain language and the British intercepted it. Admiral Percy Noble, commander of Western Approaches Command, immediately ordered several ships to race to the scene. By early afternoon, fuel levels had forced the Hudsons to return to 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 U-570s crew to take to the water, then sink her. The first vessel to reach U-570, the anti-submarine trawler HMT Northern Chief, arrived around 10:00 pm, guided to the scene by flares the Catalina dropped. The Catalina returned to Iceland after having circled U-570 for 13 hours.
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. (Northern Chiefs captain, N.L. Knight, had been ordered to prevent the submarine from being scuttled by any means.) During the night, five more Allied vessels reached the scene: the armed trawler Kingston Agate, two anti-submarine whalers,The lake-class armed whalers HMS Wastwater and HMS Windermere the Royal Navy destroyer , and the Canadian destroyer .
At daybreak, the Allies and Germans exchanged signal lamp messages, with the Germans repeatedly requesting to be taken off as they were unable to stay afloat, and the British refusing to evacuate them until the Germans 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 appeared: a Northrop N-3PB of 330 (Norwegian) Squadron).Dunmore, p. 129 Unaware of the surrender, it attacked U-570 with small bombs and fired on Northern Chief, which fired back.Blair 1996, p. 344. No damage was done and Burwell ordered the aircraft away by radio.
The weather worsened; several attempts to attach a tow-line to U-570 were unsuccessful. Believing the Germans were being obstructive, Burwell's captain, S.R.J. WoodsDunmore, p. 128 ordered a machine gunner to fire warning shots, shots that accidentally hit and slightly wounded five of the German crew. With much difficulty, an officerLieutenant H.B. Campbell, see Conyers Nesbit 2008, p.75, Blair 1996, p. 344 and three sailors from Kingston Agate reached the submarine using a Carley float (a liferaft). After a quick search failed to find the U-boat's Enigma machine, they attached a tow line and transferred the five wounded men and the submarine's officers to Kingston Agate. The remaining crew were taken on board HMCS Niagara, which by this time had come alongside U-570.
The ships began slowly sailing to Iceland with U-570 under tow, and with a relay of Hudsons and Catalinas constantly patrolling overhead. They arrived at dawn on 29 August at Þorlákshöfn. There, they beached U-570 as she had been taking on water and was thought to be in danger of sinking.
Salvage and repair Two days after U-570s arrival, a British submarine commander—Lieutenant George Robson Colvin—together with a team of engineering warrant officers and civilian technical experts, arrived at Þorlákshöfn from Britain. They then carried out the initial examination and salvage of U-570.
Colvin's team was able to restore lighting and buoyancy; a refloated U-570 was towed around the coast to the British naval base at Hvalfjörður. There U-570 was docked to the depot ship HMS Hecla for repair, with the aim that U-570 could make the trip to Britain under her own power.CB4318, Appendix 1, p. 50