HMS H21


HMS H21 was a British H class submarine built by Vickers Limited, Barrow-in-Furness, as the first of the Batch 3 H class submarines. She was laid down on 20 October 1917 and was commissioned on 28 January 1918. H21 was an improved design of the H class which produced a larger displacement and the latest 21 inch torpedo tubes replacing the old 18 inch torpedo tubes. This would be incorporated into all batch 3 H class submarines. HMS H21 was sold to John Cashmore Ltd on 13 July 1926 for scrapping at Newport.

Design

Like all post-H20 British H-class submarines, H21 had a displacement of at the surface and while submerged. It had a total length of, a beam length of, and a draught length of. It contained a diesel engines providing a total power of and two electric motors each providing power. The use of its electric motors made the submarine travel at. It would normally carry of fuel and had a maximum capacity of.
The submarine had a maximum surface speed of and a submerged speed of. Post-H20 British H-class submarines had ranges of at speeds of when surfaced. H21 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. It is a Holland 602 type submarine but was designed to meet Royal Navy specifications. Its complement was twenty-two crew members.