HMS Excalibur was the sister ship of , the two submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s being the only High test peroxide

High test peroxide

High-test peroxide or HTP is a high -concentration solution of hydrogen peroxide, with the remainder predominantly made up of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water...

 (HTP) powered submarines to be constructed by the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

. She is the only ship to be named as such, and was named in honour of the sword

Excalibur

Excalibur is the legendary sword of King Arthur, sometimes attributed with magical powers or associated with the rightful sovereignty of Great Britain. Sometimes Excalibur and the Sword in the Stone are said to be the same weapon, but in most versions they are considered separate. The sword was...

 of King Arthur

King Arthur

King Arthur is a legendary British leader of the late 5th and early 6th centuries, who, according to Medieval histories and romances, led the defence of Britain against Saxon invaders in the early 6th century. The details of Arthur's story are mainly composed of folklore and literary invention, and...

 of the Arthurian legend

Legend

A legend is a narrative of human actions that are perceived both by teller and listeners to take place within human history and to possess certain qualities that give the tale verisimilitude...

.

For details of the decisions leading to their construction, and problems affecting the vessels, please refer to the article on HMS Explorer.

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

RFA King Salvor (A291)

RFA King Salvor , initially HMS King Salvor , was the lead ship of a class of 12 salvage vessels of the Royal Fleet Auxiliary. A 13th ship was completed as a submarine rescue vessel for the Royal Navy as ....

 and a fuel carrier, RFA Spabeck

RFA Spabeck (A227)

RFA Spabeck was a coastal water carrier of the Royal Fleet Auxiliary.Spabeck, ordered in September 1941, was laid down on 14 May 1943, and launched on 21 June 1943 as Rivulet. Commissioned on 3 September 1943 as Spabeck, she was decommissioned in March 1966 after having been used to carry peroxide...

. They later acted as high speed underwater targets for the Royal Navy's prototype nuclear powered submarine HMS Dreadnought

HMS Dreadnought

Several ships and one submarine of the Royal Navy have borne the name HMS Dreadnought in the expectation that they would "dread nought", i.e. "fear nothing, but God"...

.

Periscope

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

Elie and Earlsferry

Elie and Earlsferry is a town and former royal burgh in Fife, Scotland, situated within the East Neuk beside Chapel Ness on the north coast of the Firth of Forth, eight miles east of Leven...

, Scotland; players and visitors may use it to view the golf course.