The German crew hurriedly scrambled overboard without destroying their codebooks or Enigma machine and, crucially, having failed to open all the sea-water vents to scuttle the U-boat properly. Three Royal Navy 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 (such as that of Kahn) say that they "swam naked" to "U-559", which was sinking, but slowly. Sebag-Montefiore states that they either leapt from "Petard" or, in Brown's case, from a whaler. They retrieved the U-boat's Enigma key setting sheets with all current settings for the U-boat Enigma network. 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 U-boat, attempting to get out, when it foundered; both drowned.