 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 . 
