History
Nazi Germany
Name	U-646
Ordered	20 January 1941
Builder	Blohm & Voss, Hamburg
Yard number	622
Laid down	23 December 1941
Launched	3 September 1942
Commissioned	29 October 1942
Fate	Sunk on 17 May 1943 by British aircraft south-east of Iceland
General characteristics
Class and type	Type VIIC submarine
Displacement	769 t (757 long tons) surfaced 871 t (857 long tons) submerged
Length	67.10 m (220 ft 2 in) (o/a) 50.50 m (165 ft 8 in) (pressure hull)
Beam	6.20 m (20 ft 4 in) (o/a) 4.70 m (15 ft 5 in) (pressure hull)
Height	9.60 m (31 ft 6 in)
Draught	4.74 m (15 ft 7 in)
Installed power	2,800–3,200 PS (2,100–2,400 kW; 2,800–3,200 bhp) (diesels) 750 PS (550 kW; 740 shp) (electric)
Propulsion	2 shafts 2 × diesel engines 2 × electric motors
Speed	17.7 knots (32.8 km/h; 20.4 mph) surfaced 7.6 knots (14.1 km/h; 8.7 mph) submerged
Range	8,500 nmi (15,700 km; 9,800 mi) at 10 knots (19 km/h; 12 mph) surfaced 80 nmi (150 km; 92 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged
Test depth	230 m (750 ft) Crush depth: 250–295 m (820–968 ft)
Complement	4 officers, 40–56 enlisted
Armament	5 × torpedo tubes (four bow, one stern) 14 × 53.3 cm (21 in) torpedoes or 26 TMA mines 1 × 8.8 cm (3.46 in) deck gun (220 rounds) 1 × twin 2 cm (0.79 in) C/30 anti-aircraft gun
Service record
Part of:	5th U-boat Flotilla 29 October 1942 – 31 March 1943 11th U-boat Flotilla 1 April – 17 May 1943
Identification codes:	M 49 751
Commanders:	Oblt.z.S. Heinrich Wulff 29 October 1942 – 17 May 1943
Operations:	2 patrols: 1st patrol: 28 March – 30 April 1943 2nd patrol: 12 – 17 May 1943
Victories:	None

German submarine U-646 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on 23 December 1941 at the Blohm & Voss yard at Hamburg, launched on 3 September 1942, and commissioned on 29 October 1942 under the command of Leutnant zur See d.R. Heinrich Wulff.

Attached to 5th U-boat Flotilla based at Kiel, U-646 completed her training period on 31 March 1943 and was assigned to front-line service.

German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-646 had a displacement of 769 tonnes (757 long tons) when at the surface and 871 tonnes (857 long tons) while submerged.^[1] 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).^[1]

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).^[1] 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-646 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.^[1]

While on patrol in the North Atlantic, U-646 was detected by Hudson J of No. 269 Squadron RAF south-east of Iceland on 17 May 1943. In the subsequent attack, the U-boat was sunk and all 46 crew members perished.^[2]

• Helgason, Guðmundur. "The Type VIIC boat U-646". German U-boats of WWII - uboat.net. Retrieved 21 July 2015.

62°10′N 14°30′W / 62.167°N 14.500°W / 62.167; -14.500