British S-class submarine (1931)

The 1931 British S class began as a group of four small patrol submarines, Swordfish, Sturgeon, Seahorse and Starfish, ordered to replace the older H class when the Royal Navy modernised its submarine force in the early 1930s. All four were built at Chatham Dockyard between 1930 and 1932 and served in the North Sea and off Scandinavia, where three of them were lost to mines or depth charges in 1939 and 1940. The design was repeated in larger groups at Chatham and other yards, and in all 62 boats were built over fifteen years, making it the biggest submarine class the Royal Navy ever ordered. The last British boat, Sea Devil, was scrapped in 1966.