HMS H12 was a British H-class submarine built by Fore River Yard, Quincy, Massachusetts. She was laid down on an unknown date and commissioned in 1915. HMS H12 along with HMS H11 and HMS H13 to HMS H20 were all built in America but were interned by the United States government until the United States entered World War I. HMS H12 was sold in April 1920 in Dover.

Design

Like all pre-H21 British H-class submarines, H12 had a displacement of 364 LT at the surface and 434 LT while submerged. It had a total length of 150 ft, a beam of 15 ft, and a draught of 12 ft. 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 11 kn. British H-class submarines had ranges of 1600 nmi at speeds of 10 kn. H12 was fitted with a 6 lb Hotchkiss quick-firing gun (6-pounder) and four 18 in torpedo tubes. Its torpedo tubes were fitted to the bows and the submarine was loaded with eight 18 in torpedoes. It is a Holland 602 type submarine but was designed to meet Royal Navy specifications. Its complement was twenty-two crew members.