During the modernization of the submarine force in the early 1930s, the Royal Navy became aware of the need for smaller boats, suitable for employment in the North Sea and restricted waters such as the Mediterranean. In response to this requirement, orders were placed for medium-sized patrol submarines, from which the Swordfish and Shark Classes were evolved.
Based on the saddle-tank construction of the L Class submarines, which they were designed to replace, the 12 vessels of these two classes proved so useful that an improved version was put into mass production during the Second World War. 217 feet long. and displacing 872 tons (surfaced), the improved S boats gave
