German submarine U - 559 German submarine " U - 559 " was a Type VIIC U - boat built for the Nazi German " Kriegsmarine " for service during World War II . Laid down on 1 February 1940 at the Blohm & Voss shipyards in Hamburg as " Baunummer 535 " ( " Yard number 535 " ) , she was launched on 8 January 1941 and commissioned on 27 February under " Kapitänleutnant " Hans Heidtmann . She began her service career with the 1st U - boat Flotilla , undergoing training before being declared operational on 1 June 1941 . She moved to the 29th U - boat Flotilla on 15 April 1942 . She sank five ships but is perhaps best remembered for an incident during her sinking in the Mediterranean Sea in 1942 , in which British sailors seized cryptographic material from " U - 559 " . This material was extremely valuable in breaking the U - boat Enigma cipher . Operational career . " U - 559 " was originally intended to serve as an Atlantic U - boat during the second Battle of the Atlantic against Allied convoys in the Western Approaches . 1st and 2nd patrols . Her first patrol took her from Kiel on 4 June 1941 , across the North Sea and through the gap between Greenland and Iceland . She arrived at St . Nazaire in occupied France on 5 July . Her second sortie met with success when she torpedoed and sank the " Alva " about west of Ushant . She returned to her French base on 22 August 1941 . 3rd patrol . For her third patrol , beginning on 20 September , she was assigned to the ' Goeben ' group , which were the first U - boats to enter the Mediterranean in World War II through the heavily defended Strait of Gibraltar . She reached Salamis in Greece , after having first investigated the Libyan / Egypt ian border . 4th patrol . On her fourth patrol , she torpedoed and sank the Australian sloop off the Libyan coast ; although most survivors were picked up by other ships , three men managed to reach dry land where they were rescued by advancing British troops . 5th , 6th and 7th patrols . On her fifth patrol , which began on 8 December 1941 , the boat sank on the 23rd . " Shuntien " carried 850 – 1 , 100 German and Italian prisoners of war . Between 800 and 1 , 000 people were killed , including at least 700 PoWs . Her sixth and seventh patrols were both from Salamis to the area of the Libyan coast . They were without success . 8th and 9th patrols . Having moved to Pula in Croatia in March 1942 , she then sortied on 18 May , and damaged the oiler " Brambleleaf " on 10 June . Her ninth patrol , however , was without success . Sinking . It was her own demise that made her most famous . At dawn on 30 October 1942 , " U - 559 " was spotted by a Royal Air Force Sunderland patrol aircraft from No . 47 Squadron 70 miles north of the Nile Delta . The destroyer was alerted by radio and steamed to intercept her , while the destroyers HMS , , and sailed from Port Said . " U - 559 " detected " Hero " s approach and dived . The destroyer group hunted for the U - boat for 16 hours , constantly depth charging . After dark , " U - 559 " , with a cracked pressure hull , unable to maintain level trim and four of her crew dead from explosions and flooding , was forced to the surface . She was close to " Petard " , which immediately opened fire with her 20 mm Oerlikons . The German crew hurriedly scrambled overboard without destroying their codebooks or Enigma machine and , crucially , having failed to open sea - water vents to properly scuttle the U - boat . Three British sailors , Lieutenant Anthony Fasson , Able Seaman Colin Grazier and NAAFI canteen assistant Tommy Brown , then boarded the abandoned submarine . There are differing reports as to how the three British men boarded the U - boat . Some accounts say that they " swam naked " ( such as that of Kahn ) , to " U - 559 " but Sebag - Montefiore states that they either leapt from " Petard " or , in Brown ' s case , from a whaler , which was sinking , but slowly . They retrieved the U - boat ' s Enigma machine and the codebooks with all current settings for the U - boat Enigma key . Two German crew members , rescued from the sea , watched this material being loaded into " Petard ' s " whaler but were dissuaded from interfering by an armed guard . Grazier and Fasson were inside the boat , attempting to get out , when the U - boat foundered ; both were drowned . Aftermath . Grazier and Fasson were awarded the George Cross posthumously , Brown was awarded the George Medal . The Victoria Cross was considered but not awarded , for the ostensible reason that their bravery was not " in the face of the enemy " . Another consideration may have been that a Victoria Cross would have drawn unwanted attention to the U - boat capture from German Intelligence . It was also discovered that Brown had lied about his age in order to enlist , and was only 16 years old , making him the youngest recipient of the George Medal . He was discharged and returned home to North Shields , only to die two years later attempting to rescue his younger sister from a house fire . The Enigma material they retrieved was immensely valuable to the code - breakers at Bletchley Park , who had been unable to read U - boat Enigma for nine months . The captured material allowed them to read the cyphers for several weeks , and to break U - boat Enigma thereafter . The recovery was one of several such events ( e . g . , the earlier sinking of U - 110 ) , that inspired the fictional account of the submarine capture in the 2000 film " U - 571 " .