British 21-inch torpedo

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


Torpedoes of 21 inch calibre were the largest torpedos 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 (5.448 m), and "Long" at 23 ft 1.25 in (7.042 m). The explosive charge was 200 lb (91 kg) of gun cotton increased later to 225 lb (102 kg).

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
Diameter21 in (530 mm)

Warhead weight400 to 515 lb (181 to 234 kg)

EngineWet Heater
8,000 yd (7,300 m) max depending on model
Maximum speed 29 to 35 kn (54 to 65 km/h)

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 deal) Town-class destroyers provided to the UK during the early part of the Second World War. The running speed was reduced from 45 kn (83 km/h) (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 4,500 yd (4,100 m) 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 in (530 mm)

Warhead weight515 lb (234 kg)

EngineBurner Cycle
8,000 to 13,500 yd (7,300 to 12,300 m)
Maximum speed 25 to 35 kn (46 to 65 km/h)

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
Length23 ft 4 in (7.1 m)
Diameter21 in (530 mm)

EngineWet Heater
5,000 to 13,600 yd (4,600 to 12,400 m)
Maximum speed 20 to 40 kn (37 to 74 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)
Diameter21 in (530 mm)

Warhead weight740 lb (340 kg)

EngineOxygen enriched air
5,700 yd (5,200 m)
Maximum speed 35 kn (65 km/h)

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.


Specifications: [1]

Mark VIIIs loading to Polish Navy submarine ORP Sokol Sokol torpedo.jpg
Mark VIIIs loading to Polish Navy submarine ORP Sokół


Early Mark VIII**

Late Mark VIII**

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 was used by the Royal Norwegian Navy (Coastal Artillery: Kaholmen torpedo battery at Oscarsborg Fortress) until 1993.

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

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 in (200 mm) cruisers during the war.

Mark X

From 1939, used by submarines, motor torpedo boats and destroyers from other navies such as the Grom-class destroyer.[ citation needed ]

Mark XI

Electric battery-powered torpedo with a 710 lb (322 kg) 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 750 lb (340 kg) Torpex.[ citation needed ] Using high test peroxide fuel, it attained a top speed of 28 kn (52 km/h) for 5,500 yd (5,000 m).[ citation needed ]

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.[ citation needed ]

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 (820 kg)
Length21.2 ft (6.46 m)
Diameter21 in (530 mm)

Warhead weight196 lb (89 kg)

12,000 yd (11,000 m)
Maximum speed 20 kn (37 km/h)
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 1966 although already obsolescent, and did not become fully operational until 1971, serving only as an interim before Tigerfish entered service.

The MK23 was fitted with a 10,000 m (11,000 yd) 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.


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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