German submarine U-636

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.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-636 had a displacement of 769 t when at the surface and 871 t while submerged. She had a total length of 67.10 m, a pressure hull length of 50.50 m, a beam of 6.20 m, a height of 9.60 m, and a draught of 4.74 m. The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2800 to 3200 PS for use while surfaced, two Brown, Boveri & Cie GG UB 720/8 double-acting electric motors producing a total of 750 PS for use while submerged. She had two shafts and two 1.23 m propellers. The boat was capable of operating at depths of up to 230 m.

The submarine had a maximum surface speed of 17.7 kn and a maximum submerged speed of 7.6 kn. When submerged, the boat could operate for 80 nmi at 4 kn; when surfaced, she could travel 8500 nmi at 10 kn. U-636 was fitted with five 53.3 cm torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.8 cm SK C/35 naval gun, 220 rounds, and one twin 2 cm C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.

Service history
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.

Fate
U-636 was sunk on 21 April 1945 in the North Atlantic in position 55.83333°N, -10.51667°W, by depth charges from HMS Bazely (K311), HMS Drury (K316) and HMS Bentinck (K314). All hands were lost.

Wolfpacks
U-636 took part in eleven wolfpacks, namely:
 * Iller (12 – 15 May 1943)
 * Donau 1 (15 – 26 May 1943)
 * Isegrim (1 – 7 January 1944)
 * Donner (11 – 20 April 1944)
 * Donner & Keil (20 April – 2 May 1944)
 * Trutz (28 June – 10 July 1944)
 * Dachs (1 – 5 September 1944)
 * Zorn (26 September – 1 October 1944)
 * Grimm (1 – 2 October 1944)
 * Panther (16 October – 10 November 1944)
 * Stier (4 – 15 December 1944)