British 21-inch torpedo

There have been several British 21-inch (533 mm) diameter torpedoes used by the Royal Navy since their first development just before the First World War.

The 21-inch was the largest size of torpedo in common use in the RN. They were used by surface ships and submarines rather than aircraft which used smaller 18-inch torpedoes.

Mark I

The first British 21-inch torpedo came in two lengths, "Short" at 17 ft 10.5 in (5.45 m), and "Long" at 23 ft 1.25 in (7.04 m). The explosive charge was 200 lb of gun cotton increased later to 225 lb.

Mark II

21-inch Mark II
Typeheavy torpedo
Place of originUnited Kingdom
Service history
In servicec. 1914 – Second World War
Used byRN
WarsFirst World War, Second World War
Production history
Designedc. 1910

Warhead weight400–515 lb

Enginewet heater
8,000 yards max depending on model
Speed29 to 35 knots

The Mark II, chiefly used by destroyers, entered service in 1914. Apart from some older British ships, it was used with the old US (destroyers for bases agreement) Town-class destroyers provided to the UK during the early part of the Second World War. The running speed was reduced from 45 knots (over 3,000 yards) for better reliability.

The Mark II*, an improved Mark II was used by battleships and battlecruisers. A wet heater design, it could run for 4.1 km (4,500 yd) at 45 knots (83 km/h).

Mark IV

21-inch Mark IV
Place of originUnited Kingdom
Service history
In servicec. 1916–
Production history
Designedc. 1912
Mass3,206 lb (1,454 kg)
Length22 ft 7.5 in (6.896 m)
Diameter21-inch (533 mm)

Warhead weight515 lb (234 kg)

EngineBurner cycle
8,000 – 13,500 yards
Speed25 – 35 knots

From 1912, used by destroyers and other surface ships and was an important weapon in the first World War. In the Second World War they were carried on HMS Hood.

Mark V

21-inch Mark V
Place of originUnited Kingdom
Production history
Length7.1 m (23 ft 4 in)

Enginewet heater
4.6 km (5,000 yd) to 12.4 km (13,600 yd)
Speed40 knots (74 km/h) to 25 knots (46 km/h)

The Mark V was used by the A and B-class destroyers and, with modification, by the Kent-class heavy cruisers.

Mark VII

21-inch Mark VII
Typeheavy torpedo
Place of originUnited Kingdom
Service history
In serviceSecond World War
Used byRN
Production history
Length25 ft 6 in (7.77 m)

Warhead weight740 lb (336 kg)

Engineoxygen enriched air
5,700 yards (5,200 m)
Speed35 knots

The Mark VII was issued for use on the British heavy cruisers; i.e. cruisers with 8-inch guns. Designed in the mid-1920s the County-class cruisers were built at the same time in the post Washington Naval Treaty period.

The power came from the use of oxygen enriched air, though torpedo stocks were converted to run on normal air at the start of the Second World War.




  • Entered Service: 1927
  • Weight: 3,452 lb (1,566 kg)
  • Length: 259 inches (21.6 ft) (6.58 m)
  • Explosive Charge: 750 lb (340 kg) TNT
  • Range & Speed: 5,000 yards (4,570 m) / 40 knots

Early Mark VIII**

  • Range & Speed: 5,000 yards (4,570 m) / 45.6 knots
  • Explosive Charge: 722 lb (327 kg) Torpex

Late Mark VIII**

  • Range & Speed: 7,000 yards (6,400 m) / 41 knots
  • Explosive Charge: 805 lb (365 kg) Torpex

The Mark VIII was designed around 1925 and was the first British burner-cycle design torpedo. It was used from 1927 on submarines of the O class onwards and motor torpedo boats. The principal World War II version was the improved Mark VIII**, 3,732 being fired by September 1944 (56.4% of the total number). The torpedo is still in service with the Royal Navy albeit in a limited role, and with the Royal Norwegian Navy (Coastal Artillery: Kaholmen torpedo battery at Oscarsborg Fortress) until 1993.

The Mark VIII** was used in two particularly notable incidents:

  • On 2 May 1982 the Royal Navy submarine HMS Conqueror sank the Argentine cruiser ARA General Belgrano with three Mark VIII** torpedoes during the Falklands War.[2] This is the only sinking of a surface ship by a nuclear-powered submarine in wartime (and only the second sinking of a surface ship by any submarine since the end of World War II).

Mark IX

First appeared in 1930 and was considerably improved by 1939. Used on Leander and later cruisers, "A" and later destroyer classes. Also replaced the old Mark VII in some 8" (20.3 cm) cruisers during the war.

Mark X

From 1939, used by submarines, motor torpedo boats and destroyers from other navies such as the Grom.

Mark XI

Electric battery powered torpedo with a 322 kg (710 lb) TNT warhead. Entering service during the Second World War it was used by destroyers.

Mark 12

At first codenamed Ferry, then Fancy, the Mark 12 never reached production. From 1952, it had a warhead of 340 kg (750 lb) Torpex. Using high test peroxide fuel, it attained a top speed of 28 knots (52 km/h) for 5 km (5,500 yd).

There were accidents during testing caused by the unstable nature of high test peroxide. One such engine explosion, after loading aboard the submarine HMS Sidon, caused enough damage to have the submarine taken permanently out of service.

Mark 12 torpedoes were out of service in 1959 and the programme was cancelled.[3]

Mark 20 Bidder

21-inch Mark 20
Place of originUnited Kingdom
Service history
In service1955–1980s
Production history
Designedc. 1950
Mass1,810 lb (821 kg)
Length6.46 m
Diameter21 inches

Warhead weight196 lb (89 kg)

12,000 yards (11,000 m)
Speed20 knots
passive sonar

Developed under the codename "Bidder", the Mark 20 was a passive-seeker battery-powered torpedo for use by surface ships (the Mark 20E – for "Escort") and submarines (Mark 20S). The E variant was not long in service due to problems with its programming. This led to several of the frigates that were intended to have used them (Rothesay and Whitby classes) never being fitted with torpedo tubes or having them removed.

It was replaced in the submarine service in the 1980s by Tigerfish.

Mark 21 Pentane

A project for an autonomous active/passive sonar torpedo to be carried by the Short Sturgeon anti-submarine aircraft.[4] It was cancelled after protracted work but the seeker development was used in Tigerfish.

Mark 22

A wire-guided version of the Mark 20 produced by Vickers Shipbuilding and Engineering (VSEL) as a private venture.

Mark 23 Grog

A wire-guided version of the Mark 20. Entered service in 1971 although already obsolescent, serving only as an interim before Tigerfish entered service.

The MK23 was fitted with a 10,000  m outboard dispenser that contains a control wire to guide the weapon, During 1973, all of the RN torpedoes had to be taken out of service as the control system was failing at extreme range.

After months of investigation, it was discovered that the fault lay in the Guidance Unit made by GEC. A germanium diode in the AGC circuit had been replaced by a silicon diode, following an instruction by RN stores that all germanium diodes had to be replaced by silicon diodes. Unfortunately, the silicon diode's different characteristics caused the automatic gain control circuit to fail. Once the mistake was found, replacing the diode with the original type cured the problem.

Mark 24 Tigerfish

The first Tigerfish (Mod 0) entered service in 1980. Tigerfish was removed from service in 2004.

There were several models of Tigerfish due to the modifications made to tackle deficiencies.

  • Mark 24 Mod 0 Tigerfish
  • Mark 24 Mod 1 Tigerfish
  • Mark 24(N) Tigerfish
  • Mark 24 Mod 2 Tigerfish


See also


  1. DiGiulian, Tony. "World War II Torpedoes of the United Kingdom/Britain – NavWeaps". Archived from the original on 21 February 2009.
  2. Brown, Colin; Kim Sengupta (3 April 2012). "Sinking the Belgrano: the Pinochet connection". The Independent. London. Archived from the original on 2 May 2012. Retrieved 2 May 2012.
  3. DiGiulian, Tony. "Post-World War II Torpedoes of the United Kingdom/Britain – NavWeaps". Archived from the original on 4 December 2009.
  4. "Archived copy". Archived from the original on 1 June 2009. Retrieved 5 March 2010.CS1 maint: archived copy as title (link)


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