Certificate no 3492
Status Registered


Function Fighting Vessel
Subfunction Submarine
Location Argyll
Vessel type Midget Submarine
Current use Museum based
Available to hire No
Available for excursions No
Info required No


Builder Vickers & Armstrong Ltd, Barrow
Built in 1951
Hull material
Rig None
Number of decks
Number of masts
Number of engines 1
Primary engine type Diesel
Boiler type


Length: Overall
53.83 feet (16.41 m)
Breadth: Beam
6.25 feet (1.91 m)
7.00 feet (2.13 m)
Tonnage: Gross


X51 is an X-class midget submarines developed to replace the wartime X-craft which was designed to enter enemy ports, harbors and shipping.  X51 was one of four x-class midgets ordered in 1951 but work proceeded slowly and the submarine was not launched until 01/10/54. X51 was given the name Sickleback. She was in active service until 1957 at which point she was laid up. In 1958 she was transferred to Portsmouth and on 15/07/58 sold to the Swedish Royal Navy who used her for training, renaming her Spiggen.

The X-class midget submarines carried a crew of 5 including a skipper, navigator, engineer, and two divers. They were equipped with two detachable side charges designed to cripple large enemy ships.

X51 was acquired by the Imperial War Museum in 1977 in almost complete working condition with only the battery cells and a few other parts removed. Upon acquisition in 2013 the National Museum of the Royal Navy employed preventative conservation and maintenance have been employed which are ongoing.

Key dates

  • 6/09/1951

    The submarine x51 was built

  • 1/10/1954

    X51 was ordered

  • 9/11/1954

    X51 was launched.

  • 18/01/1958

    Collision with HMS Harland Point.

  • 15/7/1958

    X51 moved to Portsmouth.

  • 1976

    X51 was sold to the Swedish Royal Navy

  • November 2013

    x51 was presented to the Imperial war Museum

  • September 2016

    Acquired by the National Museum of the Royal Navy.

  • 2017

    Placed on loan with the Scottish Submarine Heritage Center.

Own this vessel?

If you are the owner of this vessel and would like to provide more details or updated information, please contact info@nationalhistoricships.org.uk

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