SM UB-31

SM UB-31 was a German Type UB II submarine or U-boat in the German Imperial Navy (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.

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. Alternatively she may have been sunk by a mine on that date.

Design
A Type UB II submarine, UB-31 had a displacement of 274 t when at the surface and 303 t while submerged. She had a total length of 36.90 m, a beam of 4.37 m, and a draught of 3.69 m. The submarine was powered by two Benz six-cylinder diesel engines producing a total 270 PS, two Siemens-Schuckert electric motors producing 280 PS, and one propeller shaft. She was capable of operating at depths of up to 50 m.

The submarine had a maximum surface speed of 9.06 kn and a maximum submerged speed of 5.71 kn. When submerged, she could operate for 45 nmi at 4 kn; when surfaced, she could travel 7030 nmi at 5 kn. UB-31 was fitted with two 50 cm torpedo tubes, four torpedoes, and one 8.8 cm Uk L/30 deck gun. She had a complement of twenty-one crew members and two officers and a 42-second dive time.