German submarine U-631

German submarine U-631 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 5 September 1941 by Blohm & Voss, Hamburg as yard number 607, launched on 27 May 1942 and commissioned on 16 July 1942 under Oberleutnant zur See Jürgen Krüger.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-631 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 BBC 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-631 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 16 July 1942, followed by active service on 1 January 1943 as part of the 9th Flotilla for the remainder of her service. In three patrols she sank two merchant ships, for a total of.

Fate
U-631 was sunk on 17 October 1943 in the North Atlantic SE of Cape Farewell, Greenland, in position 58.21667°N, -32.48333°W, by depth charges from British corvette HMS Sunflower (K41). All crew members died.

Wolfpacks
U-631 took part in seven wolfpacks, namely:
 * Falke (28 December 1942 – 19 January 1943)
 * Landsknecht (19 – 28 January 1943)
 * Stürmer (11 – 20 March 1943)
 * Seewolf 2 (21 – 30 March 1943)
 * Meise (11 – 27 April 1943)
 * Rossbach (27 September – 9 October 1943)
 * Schlieffen (14 – 17 October 1943)