SM UB-31^{[Note 1]} was a German Type UB II submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 22 July 1915 and launched on 16 November 1915. She was commissioned into the German Imperial Navy on 25 March 1916 as SM UB-31.

Quick Facts History, German Empire ...

SM UB-45, a U-boat similar to UB-31
History
German Empire
Name	UB-31
Ordered	22 July 1915[1]
Builder	Blohm & Voss, Hamburg[1]
Cost	1,152,000 German Papiermark[2]
Yard number	255[1]
Launched	16 November 1915[1]
Completed	24 March 1916[1]
Commissioned	25 March 1916[2]
Fate	Sunk 2 May 1918 by British warships[2]
General characteristics [2]
Class and type	German Type UB II submarine
Displacement	274 t (270 long tons) surfaced 303 t (298 long tons) submerged
Length	36.90 m (121 ft 1 in) o/a 27.90 m (91 ft 6 in) pressure hull
Beam	4.37 m (14 ft 4 in) o/a 3.85 m (12 ft 8 in) pressure hull
Draught	3.69 m (12 ft 1 in)
Propulsion	1 × propeller shaft 2 × 6-cylinder diesel engine, 270 PS (200 kW; 270 bhp) 2 × electric motor, 280 PS (210 kW; 280 shp)
Speed	9.06 knots (16.78 km/h; 10.43 mph) surfaced 5.71 knots (10.57 km/h; 6.57 mph) submerged
Range	7,030 nmi (13,020 km; 8,090 mi) at 5 knots (9.3 km/h; 5.8 mph) surfaced 45 nmi (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged
Test depth	50 m (160 ft)
Complement	2 officers, 21 men
Armament	2 × 50 cm (19.7 in) torpedo tubes 4 × torpedoes (later 6) 1 × 8.8 cm (3.5 in) Uk L/30 deck gun
Notes	42-second diving time
Service record
Part of:	Baltic Flotilla 16 May 1916 – 24 February 1917 Flandern Flotilla 24 February 1917 – 2 May 1918
Commanders:	Oblt.z.S. Karl Vesper[3] 18 March – 11 August 1916 Oblt.z.S. Thomas Bieber[4] 12 August 1916 – 31 January 1918 Oblt.z.S. Wilhelm Braun[5] 1 February – 2 May 1918
Operations:	25 patrols
Victories:	27 merchant ships sunk (73,810 GRT) 8 merchant ships damaged (34,699 GRT)

Close

The submarine sank 27 ships in 25 patrols. UB-31 was depth charged and sunk by British warships HMS Lord Leitrim, HMS Loyal Friend, and HMS Ocean Roamer in the English Channel on 2 May 1918.^[2] Alternatively she may have been sunk by a mine on that date.^[6]

A German Type UB II submarine, UB-31 had a displacement of 274 tonnes (270 long tons) when at the surface and 303 tonnes (298 long tons) while submerged. She had a total length of 36.90 m (121 ft 1 in), a beam of 4.37 m (14 ft 4 in), and a draught of 3.69 m (12 ft 1 in). The submarine was powered by two Benz six-cylinder diesel engines producing a total 270 metric horsepower (270 shp; 200 kW), two Siemens-Schuckert electric motors producing 280 metric horsepower (210 kW; 280 shp), and one propeller shaft. She was capable of operating at depths of up to 50 metres (160 ft).^[2]

The submarine had a maximum surface speed of 9.06 knots (16.78 km/h; 10.43 mph) and a maximum submerged speed of 5.71 knots (10.57 km/h; 6.57 mph). When submerged, she could operate for 45 nautical miles (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 7,030 nautical miles (13,020 km; 8,090 mi) at 5 knots (9.3 km/h; 5.8 mph). UB-31 was fitted with two 50 centimetres (20 in) torpedo tubes, four torpedoes, and one 8.8 cm (3.5 in) Uk L/30 deck gun. She had a complement of twenty-one crew members and two officers and a 42-second dive time.^[2]