HMS Thermopylae (P355) was a T-class submarine of the United Kingdom's Royal Navy laid down on 26 October 1943 at Chatham Dockyard, and launched on 27 June 1945. So far she has been the only ship of the Royal Navy to bear the name Thermopylae, after the Battle of Thermopylae. Commissioned after the end of the Second World War, she had a relatively quiet career. She immediately joined the 3rd Flotilla based in the Holy Loch. In 1953 she took part in the Fleet Review to celebrate the Coronation of Queen Elizabeth II.