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There have been several British 21-inch (53 cm) diameter torpedoes used by the Royal Navy since their first development just before the First World War.

They were 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.

21 inch 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.

21 inch Mark II[]

21 inch Mark II
Type heavy torpedo
Place of origin United Kingdom
Service history
In service c. 1914- Second World War
Used by RN
Wars First World war, Second World War
Production history
Designed c. 1910
Diameter 21 inch

Warhead TNT
Warhead weight 400-515 lb

Engine wet heater
8,000 yards max depending on model
Speed 29 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) 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)

21 inch Mark IV[]

21 inch Mark IV
Type torpedo
Place of origin United Kingdom
Service history
In service c. 1916-
Production history
Designed c. 1912
Weight 3,206 lb (1,454 kg)
Length 22 ft 7.5 in (6.896 m)
Diameter 21 inch (533 mm)

Warhead TNT
Warhead weight 515 lb (234 kg)

Engine Burner cycle
8,000 - 13,500 yards
Speed 25 - 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.

21 inch Mark V[]

21 inch Mark V
Type torpedo
Place of origin United Kingdom
Production history
Designed 1917
Length 7.1 m (23 ft 4 in)
Diameter 21 inch

Engine wet heater
4.6 km (5,000 yd) to 12.4 km (13,600 yd)
Speed 40 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.

21 inch Mark VII[]

21 inch Mark VII
Type heavy torpedo
Place of origin United Kingdom
Service history
In service Second World War
Used by RN
Production history
Designed 1920s
Length 25 ft 6 in (7.77 m)
Diameter 21 inch

Warhead TNT
Warhead weight 740 lb (336 kg)

Engine oxygen enriched air
5,700 yards (5,200 m)
Speed 35 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.

21 inch Mark VIII[]


Mark VIIIs loading to Polish Navy submarine ORP Sokół


  • 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 was still in service with the Royal navy as late as 1983, and with the Royal Norwegian Navy (Coastal Artillery: Kaholmen torpedobattery at Oscarsborg fortress) until 1993.

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

On 9 February 1945 the Royal Navy submarine HMS Venturer sank the German submarine U-864 with four Mark VIII** torpedoes. This is the only intentional wartime sinking of one submarine by another while both were submerged.

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 WWII).

21 inch Mark X[]

From 1939, used by submarines, motor torpedo boats and destroyers.

21 inch 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.

21 inch Mark 12[]

Codenamed first "Ferry" then "Fancy", the Mark 12 never reached production. From 1952, a warhead of 340 kg (750 lb) Torpex. Powered by high test peroxide, giving it a speed of 28 knots (52 km/h) for 5 km (5,500 yd).

There were accidents during testing caused by the unstable nature of HTP. One such engine explosion, after loading on 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]

21 inch Mark 20 Bidder[]

21 inch Mark 20
Type torpedo
Place of origin United Kingdom
Service history
In service 1955-1980s
Production history
Designed c. 1950
Weight 1,810 lb (821 kg)
Length 6.46 m
Diameter 21 inches

Warhead weight 196 lb (89 kg)

Engine electric
Propellant battery
12,000 yards (11,000 m)
Speed 20 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 frigates intended to use 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.

21 inch 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.

21 inch Mark 22[]

A wireguided version of the Mark 20 produced by Vickers Shipbuilding and Engineering (VSEL) as a private venture

21 inch Mark 23 Grog[]

A wireguided version of the Mark 20. Entered service in the 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[]



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