were preceded by the shorter Type VIIB submarines. U-204 had a displacement of when at the surface and while submerged. She had a total length of, a pressure hull length of, a beam of, a height of, and a draught of. The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of for use while surfaced, two AEG GU 460/8–27 double-acting electric motors producing a total of for use while submerged. She had two shafts and two propellers. The boat was capable of operating at depths of up to. The submarine had a maximum surface speed of and a maximum submerged speed of. When submerged, the boat could operate for at ; when surfaced, she could travel at. U-204 was fitted with five torpedo tubes, fourteen torpedoes, one SK C/35 naval gun, 220 rounds, and a C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.
U-204s first patrol began when she left Kiel on 24 May 1941; she travelled through the gap between Greenland and Iceland and sank the Icelandic fishing boatHolsteinn with gunfire, south of Iceland on 31 May - Kell did not want news of the U-boat's presence to be broadcast. She then sank Mercier east of Newfoundland on 10 June. She docked at Brest in occupied France, on the 27th.
2nd patrol
Nearly a month passed before the boat sortied again. On 2 August she spotted Allied convoy SL81 and called for support. When arrived the following day, they attacked together but without success. On 18 Aug she joined a wolfpack searching for Convoy OG 71 and shortly after 0100 the next day she struck HNoMS Bath with two torpedoes into the starboard side of her engine room and causing the destroyer to sink within three minutes at about southwest of Ireland. Eighty-four of Baths crew including her COLieutenant Commander Frederik Melsom were killed plus two others later died after rescue; the death toll was compounded by the fact that two depth charges exploded when the vessel went down.
3rd patrol and loss
Having left Brest on 20 September 1941, she sank the Spanish sailing shipAingeru Guardakoa with a single torpedo on 14 October, thinking she was a British submarine chaser. She then sank Inverlee on the 19th. On the same day, she fell victim to a British anti-submarine sweep from Gibraltar. She was sunk by depth charges from the corvette and the sloop. Forty-six men died; there were no survivors.
