HMS/M Porpoise, first of a class of eight submarines, of which three were built in the Barrow Shipyard.A post WWII design, influenced in many ways by the German type XXI submarines, with the emphasis on speed. The design was approved in 1948, but Porpoise did not join the fleet until 1958.

Designated "Patrol Submarines", they could, with improved snorkel systems remain submerged for a greater length of time than previous boats. They were very quiet underwater, a great deal of attention having been paid to internal noise. Sonar equipment was greatly improved to produce the most modern form of listening platform in the world. Improved crew accommodation, including efficient air conditioning, allowed the boats to operate efficiently world wide, a necessity during the Cold War.

In 1983 Porpoise was placed on the disposal list. On the 20th October 1985 she was sunk as a target for the BUTEC range, in the Western Isles of Scotland.