British 21-inch torpedo

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.

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 (5.448 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
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
Specifications
Diameter	21 in (530 mm)
Warhead	TNT
Warhead weight	400 to 515 lb (181 to 234 kg)
Engine	Wet Heater
Operational range	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
Type	Torpedo
Place of origin	United Kingdom
Service history
In service	c. 1916–
Production history
Designed	c. 1912
Specifications
Mass	3,206 lb (1,454 kg)
Length	22 ft 7.5 in (6.896 m)
Diameter	21 in (530 mm)
Warhead	TNT
Warhead weight	515 lb (234 kg)
Engine	Burner Cycle
Operational range	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
Type	Torpedo
Place of origin	United Kingdom
Production history
Designed	1917
Specifications
Length	23 ft 4 in (7.1 m)
Diameter	21 in (530 mm)
Engine	Wet Heater
Operational range	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
Type	Heavy Torpedo
Place of origin	United Kingdom
Service history
In service	Second World War
Used by	RN
Production history
Designed	1920s
Specifications
Length	25 ft 6 in (7.77 m)
Diameter	21 in (530 mm)
Warhead	TNT
Warhead weight	740 lb (340 kg)
Engine	Oxygen enriched air
Operational range	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.

Mark VIII[]

Specifications:^[1]

Mark VIII

• Entered service: 1927
• Weight: 3,452 lb (1,566 kg)

• Length: 259 in (6.6 m)
• Explosive charge: 750 lb (340 kg) TNT
• Range and speed: 5,000 yd (4,600 m) at 40 kn (74 km/h)

Early Mark VIII**

• Range and speed: 5,000 yd (4,600 m) at 45.6 kn (84.5 km/h)
• Explosive charge: 722 lb (327 kg) Torpex

Late Mark VIII**

• Range and speed: 7,000 yd (6,400 m) at 41 kn (76 km/h)
• 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 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 two 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 the second (of three) sinkings of a surface ship by any submarine since the end of World War II). The other two sinkings were of the Indian frigate INS Khukri and the South Korean corvette ROKS Cheonan.

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
Type	Torpedo
Place of origin	United Kingdom
Service history
In service	1955–1980s
Production history
Designed	c. 1950
Specifications
Mass	1,810 lb (820 kg)
Length	21.2 ft (6.46 m)
Diameter	21 in (530 mm)
Warhead weight	196 lb (89 kg)
Engine	Electric
Propellant	Battery
Operational range	12,000 yd (11,000 m)
Maximum speed	20 kn (37 km/h)
Guidance system	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.

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

Spearfish[]

See also[]

• British 18-inch torpedo
• List of torpedoes

Notes[]

References[]

• Tony DiGiulian. "British torpedoes Pre World War II".
• Tony DiGiulian. "British Torpedoes of World War II".
• Tony DiGiulian. "British Torpedoes post World War II".
• https://web.archive.org/web/20100311033414/http://middle-watch.com/Torpedoes.htm