|Ordered:||5 June 1941|
|Laid down:||3 September 1942|
|Launched:||18 September 1943|
|Commissioned:||25 October 1943|
|Fate:||Sunk 7 July 1944 in the English Channel in position Coordinates: , by depth charges from HMCS Ottawa, HMCS Kootenay and HMS Statice.|
|Class and type:||Type VIIC submarine|
|Draught:||4.74 m (15 ft 7 in)|
|Complement:||4 officers, 40–56 enlisted|
|Operations:||8 June - 6 July 1944|
German submarine U-678 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 3 September 1942 by Howaldtswerke, Hamburg as yard number 827, launched on 18 September 1943 and commissioned on 25 October 1943 under Oberleutnant zur See Guido Hyronimus.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-678 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 Siemens-Schuckert GU 343/38-8 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-678 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), one 3.7 cm (1.5 in) Flak M42 and two twin 2 cm (0.79 in) C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.
The boat's career began with training at 5th U-boat Flotilla on 25 October 1943, followed by active service on 1 June 1944 as part of the 7th Flotilla for the remainder of her short service. In one patrol she sank no ships. U-678 was sunk on 7 July 1944 in the English Channel in position , by depth charges from the Canadian destroyers HMCS Ottawa, HMCS Kootenay and the Royal Navy corvette HMS Statice. All crew members died.
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