HMS Swordfish was developed to meet a requirement of Royal Navy's Submarine Committee for a large submarine capable of operating with the fleet at a surfaced speed of 20 knots. Most of the earlier British submarines had been single-hulled vessels built by Vickers and the Navy was interested in evaluating other designs. Captain Roger Keyes, Inspecting Captain of Submarines, had previously served as naval attaché in Italy and had kept abreast of Italian submarine developments, which notably included double-hulled submarines designed by Cesare Laurenti of Fiat-San Giorgio. Three boats of the S class were ordered first and Laurenti was invited to submit a design to meet the RN requirement.