German submarine U-636 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II.She was laid down on 2 October 1941 by Blohm & Voss, Hamburg as yard number 612, launched on 25 June 1942 and commissioned on 20 August 1942 under Oberleutnant zur See Hans Hildebrandt.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-636 had a displacement of 769t when at the surface and 871t while submerged. She had a total length of 67.1m (220.1feet), a pressure hull length of 50.5m (165.7feet), a beam of 6.2m (20.3feet), a height of 9.6m (31.5feet), and a draught of 4.74m (15.55feet). The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of NaNPS for use while surfaced, two Brown, Boveri & Cie GG UB 720/8 double-acting electric motors producing a total of 750PS for use while submerged. She had two shafts and two 1.23abbr=onNaNabbr=on 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-636 was fitted with five 53.30NaN0 torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.82NaN2 SK C/35 naval gun, 220 rounds, and one twin 2sp=usNaNsp=us C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.
The boat's career began with training at 5th U-boat Flotilla on 20 August 1942, followed by active service on 1 April 1943 as part of the 11th Flotilla, operating from Bergen, Norway. Just six months later, she transferred to 13th Flotilla stationed in Trondheim, Norway, for the remainder of her service.
In 15 patrols she sank one merchant ship, for a total of .
U-636 was sunk on 21 April 1945 in the North Atlantic in position 55.8333°N -41°W, by depth charges from, and . All hands were lost.
U-636 took part in eleven wolfpacks, namely: