German submarine U-645

German submarine U-645 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 17 December 1941 by Blohm & Voss, Hamburg as yard number 621, launched on 3 September 1942 and commissioned on 22 October 1942 under Leutnant zur See Otto Ferro.

German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-645 had a displacement of 769 tonnes (757 long tons) when at the surface and 871 tonnes (857 long tons) while submerged. She had a total length of 67.10 m (220 ft 2 in), a pressure hull length of 50.50 m (165 ft 8 in), a beam of 6.20 m (20 ft 4 in), a height of 9.60 m (31 ft 6 in), and a draught of 4.74 m (15 ft 7 in). The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2,800 to 3,200 metric horsepower (2,060 to 2,350 kW; 2,760 to 3,160 shp) for use while surfaced, two Brown, Boveri & Cie GG UB 720/8 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged. She had two shafts and two 1.23 m (4 ft) propellers. The boat was capable of operating at depths of up to 230 metres (750 ft).

The submarine had a maximum surface speed of 17.7 knots (32.8 km/h; 20.4 mph) and a maximum submerged speed of 7.6 knots (14.1 km/h; 8.7 mph). When submerged, the boat could operate for 80 nautical miles (150 km; 92 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 8,500 nautical miles (15,700 km; 9,800 mi) at 10 knots (19 km/h; 12 mph). U-645 was fitted with five 53.3 cm (21 in) torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.8 cm (3.46 in) SK C/35 naval gun, 220 rounds, and one twin 2 cm (0.79 in) C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.

This boat's career began with training at 5th U-boat Flotilla on 22 October 1942, followed by active service on 1 May 1943 as part of the 3rd Flotilla for the remainder of her service. In three patrols she sank two merchant ships, for a total of 12,788 gross register tons (GRT).

U-645 took part in eight wolfpacks, namely:

• Without name (5–10 May 1943)
• Isar (10 – 15 May 1943)
• Donau 1 (15 – 26 May 1943)
• Leuthen (15 – 24 September 1943)
• Rossbach (24 September – 9 October 1943)
• Coronel 2 (13 – 14 December 1943)
• Coronel 3 (14 – 17 December 1943)
• Borkum (18 – 24 December 1943)

U-645 has been missing since 12 December 1943 in the North Atlantic northwest of Spain.

U-645 was sunk on 24 December 1943 in the North Atlantic in position 45°20′N 21°40′W / 45.333°N 21.667°W / 45.333; -21.667, by depth charges from USS Schenck. All hands were lost.

• Helgason, Guðmundur. "The Type VIIC boat U-645". German U-boats of WWII - uboat.net. Retrieved 29 December 2014.