HMS Graph HMS " Graph " ( pennant number P715 ) was a German Type VIIC U - boat used by the British Royal Navy during World War II . Commissioned as the U - 570 in the German " Kriegsmarine " in mid - 1941 , she was attacked and captured on her first patrol . She provided both the Royal Navy and United States Navy with significant information on German submarines , and 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 She was withdrawn from service in 1944 due to problems maintaining her .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 an island off the west coast of Scotland . Some of the wreck was removed as scrap but some wreckage remains there 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 . The test depth of the submarine was . The main armament consisted of five torpedo tubes ; four in the bow , and the fifth in the stern . A total of 14 torpedoes could be carried – 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 a 8 . 8cm C / 35 deck gun ( with around 150 rounds of ammunition ) and a 2cm Flak 30 anti - aircraft gun . A 28 cm Stereoscopic rangefinder was carried for use with the anti - aircraft gun , and a number of machine guns were also carried . " U - 570 " was laid down by Blohm & Voss at Hamburg on 21 May 1940 . The submarine was launched on 20 March 1941 . Kriegsmarine service . The " 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 , 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 sixteen U - boats to the area . 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 . 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 . 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 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 . The " U - 570 " s inexperienced crew was not unique for the time . British interrogation of rescued crew - members of the — sunk on her first patrol in September 1941 — revealed that 41 out of 48 crew were on their first war patrol . 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 ) . Earlier that morning , she had been attacked by a Lockheed Hudson bomber of 269 Squadron , flown by Sergeant Mitchell and operating from Kaldaðarnes , Iceland . However , the Hudson ' s bomb - racks failed to release its depth charges during the attack . The boat surfaced at position at around 10 : 50 am , immediately below a second 269 Squadron Hudson . Flown by Squadron Leader James Thompson , it was patrolling the area after being summoned by radio by Mitchell . Rahmlow , who had climbed out onto the bridge , heard the approaching Hudson ' s engines and ordered a crash - dive . Thompson ' s aircraft reached the submarine before she was fully submerged and dropped its four depth charges — one detonated just from the boat . The U - boat quickly resurfaced and around ten of the crew emerged . The Hudson fired 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 . 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 . A radio request for help saw a Consolidated Catalina flying boat of 209 Squadron being scrambled at Reykjavik ; it reached the scene some 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 . 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 and the responded , but was prevented from reaching the " U - 570 " by Allied air patrols . 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 . 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 the " U - 570 " s crew to take to the water , then sink her . The first vessel to reach the U - boat — the anti - submarine trawler HMT " Northern Chief " in fact arrived at around 10pm , and was guided to the scene by flares dropped by the Catalina . The aircraft returned to Iceland after circling the U - 570 for thirteen 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 Chief " s 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 " Kingson Agate " , two anti - submarine whalers , the Royal Navy destroyer and the Canadian destroyer . 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 ( Norwegian ) Squadron ) appeared . Unaware of the surrender , it attacked the " U - 570 " with small bombs and fired on the " Northern Chief " ( which returned fire ) . 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 , S . R . J . Woods ordered warning shots to be fired with a machine gun , but five of the German crew were accidentally hit and slightly wounded . With much difficulty , an officer and three sailors from the trawler HMS " 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 carried out the transfer of the five wounded men and the submarine ' s officers to the " Kingson Agate " . The remaining crew were taken on board HMCS " Niagara " , which by this time had come alongside the U - boat . The ships began slowly sailing to Iceland with the " 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 , 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 initial examination and salvage of " U - 570 " . Colvin ' s team was able to restore lighting and buoyancy ; " U - 570 " was refloated and towed around the coast to the British naval base at Hvalfjörður , where she was docked to the depot ship HMS " Hecla " for repair so she could make the trip to Britain under her own power . 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 . 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 Enigma code breaking effort . A significant discovery was the U - boat commander ' s handbook , which provided context and background information for decrypted messages . The British , unfamiliar with German naval procedures , abbreviations and jargon , sometimes found German naval traffic hard to understand even when decrypted . " U - 570 " spent three weeks at Hvalfjörður , being repaired and taking short sea trials to test the engines and steering . Between 23 and 26 September , she was carefully inspected by two US Navy officers who had been sent from the United Kingdom to Iceland for that purpose ; one of the submarine ' s G7a torpedo es was off - loaded , handed over to the Americans and later sent to the United States . An eye - witness recalled that at one point , a Hudson bomber flew low over " U - 570 " and HMS " Hecla " , signalling with a Morse lamp , " This * * * * * * is mine . " On 29 September , the submarine set out for the UK , manned by a Royal Navy prize crew under the command of Lieutenant Colvin . Escorted by the S class destroyer HMS " Saladin " and the trawler HMS " Kingston Agate " , she sailed on the surface as her diving planes had been damaged by the beaching at Þorlákshöfn . Her arrival at Barrow - in - Furness on 3 October was filmed by Pathé News newsreel cameras , and reported in the press . The capture would later be featured in British propaganda . The capture of several other U - boats , such as the ( which had sunk whilst under tow ) was kept secret to conceal the seizure of their code - books and Enigma machine s . " 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 torpedo es 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 pistol s ( 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 . Squadron Leader Thompson , his navigator / bomb - aimer — Flying Officer John Coleman — and the pilot of the 209 Squadron Catalina - Flying Officer Edward Jewiss were all awarded the Distinguished Flying Cross on 23 September 1941 . The captain of the " Kingston Agate " , Henry L ’ Estrange , was awarded the Distinguished Service Cross for his part in the capture . 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 " Vizeadmiral " Erhard Maertens , the 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 memorised , 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 secret keyword would defeat British cryptanalysis . In fact , the British code - breakers at Bletchley Park found the extra security of the keyword procedure to be simply of " nuisance value " . The " U - 570 " s crew had indeed destroyed their Enigma machine and code - books but the Germans were unaware of the Royal Navy ' s earlier capture of the ' s secret material , thanks to which , the British had been breaking German naval cyphers since June 1941 . British code - breaking 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 U - 570 ' s officers were taken to an officers ' prisoner – of – war camp at Grizedale Hall in Cumbria . This was nicknamed the " U - boat Hotel " by the British as , during the early part of the war , the majority of prisoners were naval officers rescued from sunken U - boats . There , Rahmlow ( " in absentia " ) and the U - 570 ' s other officers were tried by a " Court of Honour " convened by other German prisoners , including captured U - boat ace Otto Kretschmer . Rahmlow and his second - in - command , Bernhard Berndt , were found " guilty of cowardice " ; the other two officers were " acquitted " . 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 . 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 – and somehow destroying her . 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 . The British placed Rahmlow in a camp with German Army and Air Force prisoners to avoid further incidents of this kind . The German high command recognized the " U - 570 " s loss could be partially blamed on the crews lack of training and experience ( during the early part of the war , U - boat training had been cut down to two months ) . Both this and mounting U - boat losses ( including many boats sunk on their first patrol ) prompted the Germans to put more resources into training . Also , existing veteran crews were broken up and dispersed amongst the U - boat fleet , so the crews of all newly commissioned boats would include a core of experienced , long - serving crewmen . Months later , the German command was still trying to discover the fate of the " U - 570 " s codebooks . A system of coded messages , hidden in the text of apparently ordinary , personal letters , was used to order Otto Kretschmer to report on this . However , they were unaware that this channel of communication with German prisoners had been discovered by the Allies . Royal Navy service . The disposition of the boat was initially uncertain . Winston Churchill was in 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 . The Americans were eager to have her , but the Royal Navy objected both to this and to Churchill ' s other idea - to have her serve in the Mediterranean with a Yugoslav crew . Instead , she was commissioned into the Royal Navy as HMS " Graph " on 19 September 1941 , and assigned the Royal Navy pennant number P715 . 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 ) , but was also a play on the German word " Graf " meaning " Count " . Trials . Once seaworthy , meticulous trials were conducted to measure every aspect of " Graph ' s " sailing and diving characteristics . Even the Zeiss binoculars found on board were carefully tested . " Graph ' s " safe diving depth was discovered to be — much deeper than the British thought for this kind of boat . At the time , Royal Navy depth charges had a maximum depth setting of so the Germans could dive out of their reach . Depth charges were soon modified to take account of this . The boat ' s acoustic and magnetic characteristics were examined by different Admiralty research establishments . The Allied technical experts found much to praise about her design and construction . " Graph ' s " auxiliary machinery was on rubber mountings , making the boat more stealthy by reducing sound transmission into the hull . In particular , her Zeiss periscope was singled out for praise by both the British and the Americans who examined the boat . The American officers who carried out her initial inspection in Iceland recommended it be copied as quickly as possible for possible US Navy use . Her underwater acoustic equipment was found to be a sophisticated array of hydrophone s that was significantly better than the British equivalents . The main criticism of the boat was poor and cramped crew accommodation , which would degrade crew performance on long patrols . In mid - 1942 , " Graph " was carefully studied by the US Navy , which then had an interest in a new , smaller submarine that would be roughly her size – around two – thirds the length and half the displacement of the Gato class boats that formed the bulk of the US submarine fleet . She was considered superior in many ways to the two , experimental Mackerel class submarine s , the existing class of small US Submarine , but the project was dropped . Full scale models of her pressure hull were constructed , and used during the summer of 1942 for underwater tests of experimental Shaped charge anti - submarine bombs . In a highly secret British project , " Graph " was also used as 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 . Active service . After completing trials under the command of Lieutenant Commander E . D . Norman , " Graph " was placed under the command of Lieutenant Peter Barnsley Marriott , who had assisted in the trials . She departed from Holy Loch for her first Royal Navy war patrol on 8 October 1942 , with the intention of patrolling the Bay of Biscay . On the afternoon of 21 October 1942 , about north - north - east of Cape Ortegal ( ) , " Graph " dived to evade a German Focke - Wulf Fw 200 long - range patrol aircraft . A loud hydrophone contact made Marriott believe a nearby submarine had likewise dived and , twelve minutes later , he observed its conning - tower against the setting sun . After a pursuing the German boat , Graph fired four torpedoes . Explosions were heard , and also banging noises , leading the British to believe they had hit the other submarine and the banging noises were caused by her breaking up as she sank . In early - 1943 , Marriott was awarded the Distinguished Service Order for " great courage , skill and determination in a successful submarine patrol " . It was only after the war that examination of German records showed the submarine attacked was the , badly damaged after being rammed by the Flower - class corvette HMS " Crocus " off the coast of West Africa . The torpedoes ' tracks were seen by German lookouts , the U - boat successfully evaded them and the torpedoes then self - detonated for unknown reasons . The commander of the " U - 333 " was Peter - Erich Cremer . In his post - war account of the attack , he suggested the rattling and banging noises heard by " Graph ' s " crew were due to the severe damage previously inflicted on the " U - 333 " . His route back to France closely hugged the Spanish coastline , a pattern followed by other U - boats , and he also believed that Marriott was aware of this and had been lying in wait . Graph ' s second war patrol was from 19 November 1942 to 8 December 1942 , also in the Bay of Biscay , and was without incident . She departed from Lerwick on her third war patrol on 24 December 1942 with three other Royal Navy submarines , their task was to patrol the waters off the coast of Norway , in the area of Altafjord . At 1am on 1 January 1943 , at the position , she sighted the German heavy cruiser " Admiral Hipper " , returning from the unsuccessful attack on Convoy JB51B , better known as the Battle of the Barents Sea . However , the " Hipper " was too far off and travelling too fast to be attacked . At 4 : 23am , she sighted two German destroyers ; the German vessels were moving erratically and at low speed . " Graph " closed to a range of and fired four torpedoes . Again , explosions convinced the British that hits had been scored and a destroyer probably sunk , but again all the shots had missed . She returned to Lerwick on 13 January 1943 . " Graph " undertook no further war patrols . In 1943 , she was assigned for training duties and command of her passed to Lt . D . Swanston . Peter Marriott went on to command HMS " Stoic " , where he was awarded a DSC . Decommissioning . Defects , exacerbated by a shortage of spare parts , led to her being placed in reserve . Also , her batteries and her MAN diesel engines had a comparatively short service life ; German submarine batteries required annual replacement , unlike British batteries which were intended to last for the lifetime of the boat . She was decommissioned from active service in February 1944 . She saw some use as a target , to determine the damage caused by depth charges in full - scale trials . After surviving these experiments , she was to be towed by the Royal Navy rescue tug HMRT " Growler " from Chatham to the Clyde for scrapping . But on 19 March 1944 her tow – rope broke in gale - force winds and , driven by wind and waves , she ran aground at a position , near Coul Point , on the west coast of Islay , Scotland . " Growler " was unable to re - float the submarine and she was abandoned . " Graph " was partially salvaged and scrapped in 1947 . In 1966 , the salvage diver Keith Jessop and others removed some more of the wreck . However , they did so without the permission of the individual who owned the wreck ' s salvage rights ; they paid £400 in compensation to the owner , but were still prosecuted and fined £50 . Some remains of HMS " Graph " still remained visible at low tide on the rocks near Saligo beach in 1970 , with the pressure casing of the conning tower and periscope tube clearly visible ( the cladding , railings and other parts had all broken off in the Atlantic storms many years before ) . Today , the remains of the wreck lie in about of water ; the site has been visited and photographed by recreational divers . One of the " Kriegsmarine " battle flags of the " U - 570 " was presented to Squadron Leader Thompson and is now part of the collection of the RAF Museum . Other surviving relics from the boat include her typewriter , held by the museum at Bletchley Park , a small celestial globe , used for navigation , that is owned by a private collector . and a German sailor ' s cap , that was taken as a souvenir by one of the officers of HMCS " Niagara " and is in the Canadian War Museum . Another battle flag is claimed to have come into the possession of a young , apprentice fitter at the Vickers Barrow shipyard and still survives .