German submarine U-31 (1936)

U-33, a typical Type VIIA boat
History
Nazi Germany
Name:	U-31
Ordered:	1 April 1935
Builder:	AG Weser, Bremen
Cost:	4,189,000 Reichsmark
Yard number:	912
Laid down:	1 March 1936
Launched:	25 September 1936
Commissioned:	28 December 1936
Recommissioned:	30 July 1940
Decommissioned:	24 March 1940
Fate:	Sunk, 11 March 1940, raised sunk again 2 November 1940
General characteristics
Class and type:	Type VIIA submarine
Displacement:	626 t (616 long tons) surfaced 745 t (733 long tons) submerged
Length:	64.51 m (211 ft 8 in) o/a 45.50 m (149 ft 3 in) pressure hull
Beam:	5.85 m (19 ft 2 in) o/a 4.70 m (15 ft 5 in) pressure hull
Height:	9.50 m (31 ft 2 in)
Draught:	4.37 m (14 ft 4 in)
Installed power:	2,100–2,310 PS (1,540–1,700 kW; 2,070–2,280 bhp) (diesels) 750 PS (550 kW; 740 shp) (electric)
Propulsion:	2 shafts 2 × diesel engines 2 × electric motors
Range:	6,200 nmi (11,500 km; 7,100 mi) at 10 knots (19 km/h; 12 mph) surfaced 73–94 nmi (135–174 km; 84–108 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged
Test depth:	220 m (720 ft) Crush depth: 230–250 m (750–820 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) 11 × torpedoes or 22 TMA mines 1 × 8.8 cm (3.46 in) deck gun (220 rounds) 1 × 2 cm (0.79 in) AA gun
Service record
Part of:	2nd U-boat Flotilla 28 December 1936 – 2 November 1940
Identification codes:	M 28 961
Commanders:	Kptlt. Rolf Dau 28 December 1936 – 8 November 1938 Kptlt. Johannes Habekost 8 November 1938 – 11 March 1940 Wilfried Prellberg 8 July 1940 – 2 November 1940
Operations:	Seven: 1st patrol: 27 August – 2 September 1939 2nd patrol: 9 September – 2 October 1939 3rd patrol: 21–31 October 1939 4th patrol: 19 November – 11 December 1939 5th patrol: 15 January – 4 February 1940 6th patrol: 16 September – 8 October 1940 7th patrol: 19 October – 2 November 1940
Victories:	11 commercial ships sunk (27,751 GRT) two auxiliary warships sunk (160 GRT) one warship damaged (33,950 GRT)

German submarine U-31 was a Type VIIA U-boat of Nazi Germany's Kriegsmarine during World War II. She was laid down on 1 March 1936 as yard number 912, launched on 25 September and commissioned on 28 December 1936.

As one of the first ten German Type VII submarines later designated as Type VIIA submarines, U-31 had a displacement of 626 tonnes (616 long tons) when at the surface and 745 tonnes (733 long tons) while submerged. She had a total length of 64.51 m (211 ft 8 in), a pressure hull length of 45.50 m (149 ft 3 in), a beam of 5.85 m (19 ft 2 in), a height of 9.50 m (31 ft 2 in), and a draught of 4.37 m (14 ft 4 in). The submarine was powered by two MAN M 6 V 40/46 four-stroke, six-cylinder diesel engines producing a total of 2,100 to 2,310 metric horsepower (1,540 to 1,700 kW; 2,070 to 2,280 shp) for use while surfaced, two BBC 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 knots (31 km/h; 20 mph) and a maximum submerged speed of 8 knots (15 km/h; 9.2 mph). When submerged, the boat could operate for 73–94 nautical miles (135–174 km; 84–108 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 6,200 nautical miles (11,500 km; 7,100 mi) at 10 knots (19 km/h; 12 mph). U-31 was fitted with five 53.3 cm (21 in) torpedo tubes (four fitted at the bow and one at the stern), eleven torpedoes, one 8.8 cm (3.46 in) SK C/35 naval gun, 220 rounds, and an anti-aircraft gun. The boat had a complement of between forty-four and sixty.