HMS H31 survived until World War II. During the war, she took part in the operation to keep the in Brest, France in december 1941 before the "Channel Dash" to German homeports in the company of and 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.[1]
Like all post-H20 British H-class submarines, H31 had a displacement of 423LT at the surface and 510LT while submerged.[2] It had a total length of 171feet,[3] a beam of 15feet, and a draught of . It contained a diesel engines providing a total power of and two electric motors each providing power.[4] The use of its electric motors made the submarine travel at 11kn. It would normally carry 16.4LT of fuel and had a maximum capacity of 18LT.[5]
The submarine had a maximum surface speed of 13kn and a submerged speed of 10.5kn. Post-H20 British H-class submarines had ranges of 2985nmi at speeds of 7.5kn when surfaced.[2] [4] H31 was fitted with an anti-aircraft gun and four torpedo tubes. Its torpedo tubes were fitted to the bows and the submarine was loaded with eight torpedoes.[2] It is a Holland 602 type submarine but was designed to meet Royal Navy specifications. Its complement was twenty-two crew members.[2]