HMS Excalibur

HMS Excalibur was an, the sister ship of, the only two submarines powered by high-test peroxide which were constructed for the Royal Navy. She is the only commissioned ship in the Royal Navy to be named as such, in honour of the sword of Arthurian legend. In 2025, the Royal Navy christened a non-commissioned uncrewed submarine of the same name into service for the purpose of testing unmanned underwater systems.

Operation

Both Excalibur and Explorer were assigned to the 3rd Submarine Squadron. However, due to their experimental nature, they tended to operate independently, accompanied by their depot ship HMS Kingfisher and the fuel carrier RFA Spabeck. They later acted as high-speed underwater targets for the Royal Navy's prototype nuclear-powered submarine.

The submarine's periscope survives. It was installed in the starter's hut at the Golf House Club, the golf club at Elie and Earlsferry, Scotland; players and visitors may use it to view the golf course.