German submarine U-55 was a Type VIIB U-boat of Nazi Germany's Kriegsmarine during World War II. She was ordered on 16 July 1937 and laid down on 2 November 1938 at Friedrich Krupp Germaniawerft in Kiel as yard number 590. Launched on 19 October 1939, she went into service on 21 November 1939 under the command of Kapitänleutnant (Kptlt.) Werner Heidel.

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U-52, a typical Type VIIB boat
History
Nazi Germany
Name	U-55
Ordered	16 July 1937
Builder	Germaniawerft, Kiel
Cost	4,439,000 Reichsmark
Yard number	590
Laid down	2 November 1938
Launched	19 October 1939
Commissioned	21 November 1939
Fate	Sunk 30 January 1940
General characteristics
Class and type	Type VIIB U-boat
Displacement	753 t (741 long tons) surfaced 857 t (843 long tons) submerged
Length	66.50 m (218 ft 2 in) o/a 48.80 m (160 ft 1 in) pressure hull
Beam	6.20 m (20 ft 4 in) o/a 4.70 m (15 ft 5 in) pressure hull
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	17.9 knots (33.2 km/h; 20.6 mph) surfaced 8 knots (15 km/h; 9.2 mph) submerged
Range	8,700 nmi (16,112 km; 10,012 mi) at 10 knots (19 km/h; 12 mph)surfaced 90 nmi (170 km; 100 mi) at 4 knots (7.4 km/h; 4.6 mph)
Test depth	230 m (750 ft) Calculated crush depth: 250–295 m (820–968 ft)
Complement	4 officers, 40–56 enlisted
Sensors and processing systems	Gruppenhorchgerät
Armament	5 × 53.3 cm (21 in) torpedo tubes (four bow, one stern) 14 × torpedoes or 26 TMA mines 1 × 8.8 cm (3.46 in) deck gun (220 rounds) 1 × 2 cm (0.79 in) anti-aircraft gun
Service record
Part of:	7th U-boat Flotilla 21 November 1939 – 30 January 1940
Identification codes:	M 38 070
Commanders:	Kptlt. Werner Heidel 21 November 1939 – 30 January 1940
Operations:	1 patrol: 16 – 30 January 1940
Victories:	6 merchant ships sunk (15,853 GRT)

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German Type VIIB submarines were preceded by the shorter Type VIIA submarines. U-55 had a displacement of 753 tonnes (741 long tons) when at the surface and 857 tonnes (843 long tons) while submerged.^[1] She had a total length of 66.50 m (218 ft 2 in), a pressure hull length of 48.80 m (160 ft 1 in), a beam of 6.20 m (20 ft 4 in), a height of 9.50 m (31 ft 2 in), and a draught of 4.74 m (15 ft 7 in). The submarine was powered by two MAN M 6 V 40/46 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 AEG GU 460/8-276 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 17.9 knots (33.2 km/h; 20.6 mph) and a maximum submerged speed of 8 knots (15 km/h; 9.2 mph).^[1] When submerged, the boat could operate for 90 nautical miles (170 km; 100 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 8,700 nautical miles (16,100 km; 10,000 mi) at 10 knots (19 km/h; 12 mph). U-55 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 2 cm (0.79 in) anti-aircraft gun The boat had a complement of between forty-four and sixty.^[1]

U-55 began her first and only war patrol on 16 January 1940, under Heidel's command; he had previously sunk two ships in U-7. She sank four small freighters sailing independently, then attacked convoy OA-80G on 29 January. U-55 sank two more ships before coming under concerted attack from the convoy's escorts, supported by a Sunderland flying boat from RAF Coastal Command 228 Squadron.