German submarine U-731

German submarine U-731 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on 1 October 1941 at the Schichau-Werke yard at Danzig, launched on 25 July 1942, and commissioned on 3 October 1942 under the command of Oberleutnant zur See Werner Techand.

Attached to 8th U-boat Flotilla based at Kiel, U-731 completed her training period on 30 April 1943 and was assigned to front-line service.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-731 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 AEG GU 460/8–27 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-731 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 two twin 2 cm C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.

Service history
On the fourth and final war patrol, U-731 was detected on 15 May 1944 by two Catalinas, P-14 and P-1, of VP-63 off Tangiers, when the U-boat tried to force the Strait of Gibraltar. Two British patrol craft, HMS Kilmarnock and HMS Blackfly (FY117), received reports of the U-boat and attacked with hedgehogs. U-731 was sunk in position 35.9°N, -5.75°W; all 54 crew members perished in the attack.