X-class submarine

X24 on display at the Royal Navy Submarine Museum
Class overview
Name: X class
Operators:  Royal Navy
Preceded by: V class
Succeeded by: XE class
Subclasses: X3, X4, X5-10, X20-25, XT
Completed: 20
Lost: 7 (5 scuttled, 1 foundered, 1 collision)
Preserved: 1
General characteristics (X class)
Type: midget submarine
  • 27 tons surfaced
  • 30 tons submerged
Length: 51.25 ft (15.62 m)
Beam: 5.75 ft (1.75 m)
Draught: 5.3 ft (1.60 m)
  • Single shaft; 1 × Gardner 4LK[1] 4-cyl diesel engine, 42 hp (31.3 kW) at 1,800 rpm
  • 1 × Keith Blackman electric motor, 30 hp (22.3 kW) at 1,650 rpm
  • 6.5 knots (12.0 km/h) surfaced
  • 5.5 knots (10.2 km/h) submerged
  • 500 nmi (926 km) surfaced
  • 82 nmi (151.8 km) @2 knots (2 mph; 4 km/h) submerged
Test depth: 300 ft (91.5 m)
Complement: 4
Armament: 2 × 4,400 lb detachable amatol charges

The X class was a World War II midget submarine class built for the Royal Navy during 194344.

Known individually as X-Craft, the vessels were designed to be towed to their intended area of operations by a full-size 'mother' submarine - (usually one of the T class or S class) - with a passage crew on board, the operational crew being transferred from the towing submarine to the X-Craft by dinghy when the operational area was reached, the passage crew returning with the dinghy to the towing submarine. Once the attack was over, the X-Craft would rendezvous with the towing submarine and then be towed home. Range was limited primarily by the endurance and determination of their crews, but was thought to be up to 14 days in the craft or 1,500 miles (2,400 km) distance after suitable training. Actual range of the X-Craft itself was 500 nmi (930 km) surfaced and 82 nmi (152 km) at 2 knots (3.7 km/h) submerged.


The craft was about 51 feet (15.5 m) long, 5.5 feet (1.68 m) in maximum diameter and displaced 27 tons surfaced and 30 tons submerged. Propulsion was by a 4-cylinder Gardner 4LK [1] 42 hp diesel engine, converted from a type used in London buses, and a 30 hp electric motor, giving a maximum surface speed of 6.5 knots (12 km/h), and a submerged speed of 5.5 knots (10.1 km/h). The crew initially numbered threecommander, pilot and ERA (Engine Room Artificer, i.e. engineer) but soon a specialist diver was added, for which an airlock, known as a wet and dry compartment, was provided. The ERA, usually a Navy Chief Petty Officer, operated most of, and maintained all of, the machinery in the vessel.

The weapons on the "X-Craft" were two side-cargoes - explosive charges held on opposite sides of the hull with two tons of amatol in each. The intention was to drop these on the sea bed underneath the target and then escape. The charges were detonated by a time fuse.

The craft were fitted with electro-magnets to evade detection by anti-submarine detectors on the sea bed.


A number of development craft were built before it was felt that a feasible weapon had been produced. The first operational craft was X3 (or HM S/M X.3), launched on the night of March 15, 1942. Training with the craft began in September 1942, with X4 arriving in October. In December 1942 and January 1943 six of the "5-10" class began to arrive, identical externally but with a completely reworked interior.

These operations were part of a longer series of frogman operations, see human torpedo.

The operational base and training establishment was HMS Varbel at the former Kyles Hydro Hotel at Port Bannatyne on the Isle of Bute in the Inner Hebrides of Scotland. Their first deployment was Operation Source in September, 1943, an attempt to neutralise the heavy German warships based in Northern Norway. Six X-Craft were used, but only 2 successfully laid charges (under the German battleship Tirpitz); the rest were lost, scuttled or returned to base. Tirpitz was badly damaged and out of action until April 1944.

This was the only multiple X-craft attack. The lost craft were replaced early in 1944 with X20 to X25 and six training-only craft.

On April 15, 1944 X24 attacked the Laksevåg floating dock at Bergen. X22 was intended for the mission, but had been accidentally rammed during training and sunk with all hands. X24 made the approach and escaped successfully, but the charges were placed under Bärenfels, a 7,500 ton merchant-vessel along the dock, which was sunk; the dock suffered only minor damage. On September 11, 1944, the operation was repeated by X24, with a new crew; this time the dock was sunk.

A hand-held, hydraulically powered, net cutter of the type used by X boat divers to cut through torpedo nets protecting harbours

X-Craft were involved in the preparatory work for Overlord. Operation Postage Able was planned to take surveys of the landing beaches with X20, commanded by Lt KR Hudspeth, spending four days off the French coast. Periscope reconnaissance of the shoreline and echo-soundings were performed during daytime. Each night, X20 would approach the beach and 2 divers would swim ashore. Soil samples were collected in condoms. The divers went ashore on two nights to survey the beaches at Vierville-sur-Mer, Moulins St Laurent and Colleville-sur-Mer in what became the American Omaha Beach. On the third night, they were due to go ashore off the Orne Estuary (Sword Beach), but by this stage fatigue (the crew and divers had been living on little more than benzedrine tablets) and the worsening weather caused Hudspeth to shorten the operation, returning to Dolphin on 21 January 1944. Hudspeth received a bar to his DSC.

X20 and X23 acted as lightships to help the D-Day invasion fleet land on the correct beaches (Operation Gambit), as part of the Combined Operations Pilotage Parties (COPP).

X24 is the only remaining intact example of an X-Craft. It can be found in the Royal Navy Submarine Museum.

Operations continued in the Far East with the revised XE class submarines.

X-craft and crews

The engine of X24


The remains of an XT-class craft on the beach at Aberlady Bay in 2008. The bow is to the left, the stern to the right. From left to right can be seen the wet and dry chamber hatch, the "conning tower" (the periscopes penetrated the hull through the "eye" shape) and the secondary hatch.

The numbering sequence of the X class began with X3 because the designations X1 and X2 had already been used previously - X1 had been a one-off submarine cruiser design from the 1920s while X2 had been assigned to a captured Italian submarine.

Surviving examples

The interior of X24

In media

This type of midget submarine was portrayed in the 1955 war film, Above Us the Waves, featuring John Mills, which was based on both Operation Source, and the earlier Chariot attacks on the Tirpitz.

This class of submarine was later featured in the 1968 movie Submarine X-1 starring James Caan as a Canadian Royal Naval Volunteer Reserve officer who after losing his submarine and fifty crew members in a battle with a German ship during World War II, gets a second chance training crews to take part in a raid using midget subs.

See also


  1. 1 2 http://www.gardnerengineforum.co.uk/Web%20PDF%20Versions/Newsletter%2011.pdf
  2. "Submarine Casualties Booklet". U.S. Naval Submarine School. 1966. Retrieved 2009-09-08.
  3. Grove, Eric. Sea Battles in Close-up: World War 2, Volume 2 (Shepperton, Surrey: Ian Allan, 1993), pp.124 & 128.
  4. 1 2 3 4 5 6 7 Grove, p.127.
  5. 1 2 Grove, p.124.
  6. Grove, pp.127 & 128.
  7. Magennis earned a VC in the midget submarine attack on Takao. Grove, p.127.
  8. Supplement to THE London Gazette, p.996 of the article or p.4 of the PDF file
  9. Grove, p.128.
  10. Supplement to The London Gazette, p.996 of article or p.4 of PDF file
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