HMS H31 was a British H class submarine built by Vickers Limited, Barrow-in-Furness. She was laid down on 19 April 1917 and was commissioned on 21 February 1919. HMS H31 survived until World War II. During the war, she took part in the operation to keep the GERMAN BATTLESHIP Scharnhorst in Brest, France in december 1941 before the "Channel Dash" to German homeports in the company of GERMAN BATTLESHIP Gneisenau and GERMAN CRUISER Prinz Eugen in February 1942. During the operation, H31 was sunk by unknown causes, but most believe she was mined in the Bay of Biscay after leaving port on 19 December and failing to respond on 24 December 1941.

Design

Like all post-H20 British H-class submarines, H31 had a displacement of 423 LT at the surface and 510 LT while submerged. It had a total length of 171 ft, a beam of 15 ft, and a draught of 12 m. It contained a diesel engines providing a total power of 480 hp and two electric motors each providing 320 hp power. The use of its electric motors made the submarine travel at 11 kn. It would normally carry 16.4 LT of fuel and had a maximum capacity of 18 LT. The submarine had a maximum surface speed of 13 kn and a submerged speed of 10.5 kn. Post-H20 British H-class submarines had ranges of 2985 nmi at speeds of 7.5 kn when surfaced. H31 was fitted with an anti-aircraft gun and four 21 in torpedo tubes. Its torpedo tubes were fitted to the bows and the submarine was loaded with eight 21 in torpedoes. It is a Holland 602 type submarine but was designed to meet Royal Navy specifications. Its complement was twenty-two crew members.