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British 21-inch torpedo

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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)

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 torpedoes 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

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

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

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

Mark VII

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 VIIIs loading to Polish Navy submarine ORP Sokół
Mark VIIIs loading to Polish Navy submarine ORP Sokół


  • 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 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:

Discover more about Mark VIII related topics

Polish Navy

Polish Navy

The Polish Navy is the naval branch of the Polish Armed Forces. The Polish Navy consists of 46 ships and about 12,000 commissioned and enlisted personnel. The traditional ship prefix in the Polish Navy is ORP.

ORP Sokół (1940)

ORP Sokół (1940)

ORP Sokół was a U-class submarine built by Vickers-Armstrong at Barrow-in-Furness. Shortly after launching in September 1940 she was to be commissioned by the Royal Navy as HMS Urchin, but instead was leased to the Polish Navy due to a lack of experienced submarine crews. A sister boat to Dzik, both boats operated in the Mediterranean from Malta, where they became known as the "Terrible Twins".

Motor torpedo boat

Motor torpedo boat

A motor torpedo boat is a fast torpedo boat, especially of the mid 20th century. The motor in the designation originally referred to their use of petrol engines, typically marinised aircraft engines or their derivatives, which distinguished them from other naval craft of the era, including other torpedo boats, that used steam turbines or reciprocating steam engines. Later, diesel-powered torpedo boats appeared, in turn or retroactively referred to as "motor torpedo boats" for their internal combustion engines, as distinct from steam powered reciprocating or turbine propulsion.

Royal Navy

Royal Navy

The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against France. The modern Royal Navy traces its origins to the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.

Oscarsborg Fortress

Oscarsborg Fortress

Oscarsborg Fortress is a coastal fortress in the Oslofjord, close to the small town of Drøbak in Viken county, Norway. The best known part is situated on two small islets. The main artillery batteries are on the island Håøya and smaller batteries on the mainland to the west and east in the fjord and was military territory until 2003 when it was made a publicly available resort island. The fortress is best known for sinking the German heavy cruiser Blücher on 9 April 1940. In 2014, Oscarsborg Fortress was given protected status.

HMS Venturer (P68)

HMS Venturer (P68)

HMS Venturer was a Second World War British submarine of the V class that sank two German U-boats and five merchant ships during the war. Following the war, the boat was sold to Norway and was renamed HNoMS Utstein. She was discarded in 1964.

German submarine U-864

German submarine U-864

German submarine U-864 was a Type IXD2 U-boat of Nazi Germany's Kriegsmarine in World War II. On 9 February 1945, it became the only submarine in history to be sunk by an enemy submarine while both were submerged. U-864 was sunk by the British submarine HMS Venturer, and all 73 men on board died.

HMS Conqueror (S48)

HMS Conqueror (S48)

HMS Conqueror was a British Churchill-class nuclear-powered fleet submarine which served in the Royal Navy from 1971 to 1990. She was the third submarine of her class, following the earlier Churchill and Courageous, that were all designed to face the Soviet threat at sea. She was built by Cammell Laird at Birkenhead.

ARA General Belgrano

ARA General Belgrano

ARA General Belgrano (C-4) was an Argentine Navy light cruiser in service from 1951 until 1982. Originally commissioned by the U.S. Navy as USS Phoenix, she saw action in the Pacific theatre of World War II before being sold to Argentina. The vessel was the second to have been named after the Argentine founding father Manuel Belgrano (1770–1820). The first vessel was a 7,069-ton armoured cruiser completed in 1896.

Falklands War

Falklands War

The Falklands War was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British dependent territories in the South Atlantic: the Falkland Islands and its territorial dependency, South Georgia and the South Sandwich Islands. The conflict began on 2 April, when Argentina invaded and occupied the Falkland Islands, followed by the invasion of South Georgia the next day. On 5 April, the British government dispatched a naval task force to engage the Argentine Navy and Air Force before making an amphibious assault on the islands. The conflict lasted 74 days and ended with an Argentine surrender on 14 June, returning the islands to British control. In total, 649 Argentine military personnel, 255 British military personnel, and three Falkland Islanders were killed during the hostilities.



India, officially the Republic of India, is a country in South Asia. It is the seventh-largest country by area and the second-most populous country. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west; China, Nepal, and Bhutan to the north; and Bangladesh and Myanmar to the east. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives; its Andaman and Nicobar Islands share a maritime border with Thailand, Myanmar, and Indonesia.

INS Khukri (F149)

INS Khukri (F149)

INS Khukri was a Type 14 (Blackwood-class) frigate of the Indian Navy. She was sunk off the coast of Diu, Gujarat, India by the Pakistan Navy Daphné-class submarine Hangor on 9 December 1971 during the Indo-Pakistani War of 1971. This was the first warship sunk in action by a submarine since World War II. It remains the post-Independence Indian navy's only warship to be lost in war.

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.

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. Using high test peroxide fuel, it attained a top speed of 28 kn (52 km/h) for 5,500 yd (5,000 m).

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

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.

Discover more about Mark 20 Bidder related topics

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


Source: "British 21-inch torpedo", Wikipedia, Wikimedia Foundation, (2022, November 27th),

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  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 23 June 2015. 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. ^ "Name". Archived from the original on 1 June 2009. Retrieved 5 March 2010.

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