HMS Excalibur

HMS Excalibur was an Explorer-class submarine, the sister ship of HMS Explorer, the two submarines being the only high-test peroxide (HTP) powered submarines to be 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.^[3]

HMS Excalibur (S40)
History
United Kingdom
Name	Excalibur
Ordered	26 August 1947
Builder	Vickers Armstrong[1]
Launched	25 February 1955
Completed	22 February 1958
Identification	Pennant number: S40
Nickname(s)	The Excruciator[2]
Fate	Scrapped, 1968
Notes	Built at a cost of £1,142,000
General characteristics
Class & type	Explorer-class submarine
Displacement	780 long tons (790 t) (surfaced) 1,000 long tons (1,000 t) (submerged)
Length	178 ft (54 m)
Beam	15 ft 8 in (4.78 m)
Draught	11 ft (3.4 m)
Propulsion	High Test Peroxide (HTP) steam raising plant driving steam turbines (submerged) Diesel-electric (surfaced) 2 shafts
Speed	25 knots (46 km/h; 29 mph) (submerged)
Complement	41
Armament	None

Operation

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

Periscope

The periscope at the golf course, used to see over an adjacent sand dune and tell if the first green is clear

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.^[4]