British 21-inch torpedo

There have been a number of 21-inch (53.3cm) torpedoes in service with the Royal Navy of the United Kingdom.

Torpedoes of 21-inch caliber were the largest torpedoes in common use in the RN. They were used by surface ships and submarines; aircraft used smaller 18-inch torpedoes.

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 (91 kg) of guncotton, increased later to 225 lb (102 kg). The torpedoes were first deployed in the field in 1912 and primarily used by the Beagle class destroyers throughout most of their service during the First World War.^[1]

Specifications:^[2][3]

Mark I Short

• Entered service: 1910
• Weight: 2,100 lb (950 kg)
• Length: 17 ft 10.5 in (5.448 m)
• Explosive charge: 200 lb (91 kg) Wet guncotton
• Range and speed: 7,500 yd (6,900 m) at 16 kn (30 km/h), 1,000 yd (910 m) at 27 kn (50 km/h)

Mark I Long

• Entered service: 1910
• Weight: 2,800 lb (1,300 kg)
• Length: 23 ft 1.25 in (7.0422 m)
• Explosive charge: 200 lb (91 kg) Wet guncotton
• Range and speed: 12,000 yd (11,000 m) at 16 kn (30 km/h), 1,000 yd (910 m) at 27 kn (50 km/h)

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).

21-inch Mark IV
Type	Torpedo
Place of origin	United Kingdom
Service history
In service	c. 1916 – Second World War
Used by	RN
Wars	First World War, Second World War
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	Wet Heater
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)

The Mark IV torpedo was the principal British torpedo of World War I. From 1912, used by destroyers, torpedo boats, and other surface ships equipped with 21-inch torpedo tubes, such as the Royal Sovereign class battleships. In the Second World War they were carried as auxiliary armament on submarines and various surface ships, including HMS Hood.

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.

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.

The Mark VIII was designed circa 1925 and was the first British burner cycle design torpedo. It was used from 1927 on all submarines, beginning with the later versions of the L class and the Odin class, as well as 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 in a training role until recently, and was used by the Royal Norwegian Navy (Coastal Artillery: Kaholmen torpedo battery at Oscarsborg Fortress) until 1993.^[4]

Specifications:^[5]

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)

Mark VIII**

• Explosive charge: 722 lb (327 kg) Torpex, later increased to 805 lb (365 kg) Torpex
• Range and speed: 5,000 yd (4,600 m) at 45.6 kn (84.5 km/h), 7,000 yd (6,400 m) at 41 kn (76 km/h)

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 remains the only historically acknowledged intentional 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.^[6] 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.

The Mark IX was designed circa 1928 and first deployed in 1930. The design was considerably improved by 1939. The Mark IX was a larger and longer-range sibling to the Mark VIII, employing a very similar four-cylinder radial kerosene-air burner-cycle propulsion system. Used on the Leander class cruisers and later cruisers, A and B class destroyers, and later destroyer classes. Also replaced the old Mark VII torpedo in some 8 in (200 mm) gun cruisers during the war. The Mark IX torpedo remained in service throughout the 1960s.^[7]

Specifications:^[8]

Mark IX

• Entered service: 1930
• Weight: 3,732 lb (1,693 kg)
• Length: 286.5 in (7.28 m)
• Explosive charge: 750 lb (340 kg) TNT
• Range and speed: 10,500 yd (9,600 m) at 36 kn (67 km/h), 13,500 yd (12,300 m) at 30 kn (56 km/h)

Mark IX*

• Explosive charge: 805 lb (365 kg) Torpex
• Range and speed: 11,000 yd (10,000 m) at 36 kn (67 km/h), 14,000 yd (13,000 m) at 30 kn (56 km/h)

Mark IX**

• Explosive charge: 805 lb (365 kg) Torpex
• Range and speed: 11,000 yd (10,000 m) at 41 kn (76 km/h), 15,000 yd (14,000 m) at 35 kn (65 km/h)

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

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

A design for a high-speed torpedo propelled by high-test peroxide (HTP), based on wartime research by Hellmuth Walter during the Second World War. At first codenamed Ferry, then Fancy, the Mark 12 never moved past the prototype stage. The design was conceived in 1945, after the end of the war in Europe, with the arrival of technical documentation from Germany. For economical reasons, the Mark VIII torpedo body was used, in an effort to adapt it to HTP propulsion.^[9] The Ferry was supposed to be a surface-running torpedo with a gyroscopically-guided search pattern. Prototypes of the weapon were ready in 1953, except for the pattern-running feature, which was then omitted and the weapon was redesignated as Fancy. In 1954, several prototypes were issued to HMS Maidstone and over 200 test runs were carried out until a catastrophic accident. On 16 June 1955, the HMS Sidon was alongside HMS Maidstone in Portland Harbor, preparing to make way to Stage II trials of the Fancy. Crewmen on the submarine were in the process of loading one of the prototype torpedoes into a launch tube, when the stop valve on the weapon was accidentally opened, triggering the release of reactant in its propulsion unit. The weapon exploded inside the launch tube, simultaneously blowing out the bow caps as well as the rear hatch of the launch tube. A blast of debris and dense carbon dioxide were propelled into the submarine. Two officers and ten seamen were killed instantly, six from the initial blast and six more by asphyxiation from the ejected gases. One more victim, a doctor from the Maidstone, subsequently perished in an effort to rescue the crew from the submarine. The submarine sank in shallow water due to flooding from the blown-open launch tube. Ultimately the accident caused enough damage to have the submarine taken permanently out of service.^[10] Following this accident, a second Mark 12 Fancy exploded at the Arrochar torpedo range in Loch Long, Scotland. As a consequence of these accidents, and the perceived hazardous nature of HTP propulsion, the program was cancelled in 1959.

Specifications:^[11]

Mark 12

• Prototype date: 1952
• Weight: 3,452 lb (1,566 kg)
• Length: 254.5 in (6.46 m)
• Explosive charge: 750 lb (340 kg) Torpex
• Range and speed: Unknown, above 40 kn (74 km/h)

21-inch Mark 20
A Mark 20 torpedo exhibit at the Clandestine Immigration and Naval Museum, Haifa, Israel.
Type	Torpedo
Place of origin	United Kingdom
Service history
In service	1955–1988
Used by	RN
Production history
Designed	1945
Specifications
Mass	1,810 lb (820 kg)
Length	13.5 ft (4.11 m)
Diameter	21 in (530 mm)
Warhead	Torpex
Warhead weight	196 lb (89 kg)
Engine	Electric
Propellant	Battery (perchloric acid)
Operational range	12,000 yd (11,000 m)
Maximum speed	20 kn (37 km/h)
Guidance system	Passive Sonar

The Mark 20 was a passive-seeker battery-powered torpedo which was initially conceived in 1945, as a 21-inch development of the 18-inch Dealer project for a parachute-dropped ASW weapon, conceived in 1943.^[12] At the end of the Second World War the Dealer project was renamed Dealer A and became further branched out into the 21-inch Bidder and 18-inch Dealer B projects.^[13] Thus, the Mark 20 was developed alongside the 18-inch Mark 30 Dealer B and shared elements of its design.^[14] The development program was elevated in scope and priority after the cancellation of the Mark 21 Pentane. Two variants were developed: the Mark 20S ("Submarine") for use by submarines, and a larger Mark 20E ("Escort") for use by surface ships. The S variant had a single speed of 20 knots, and the E variant had a dual-speed mode of 15 knots and 24 knots, for target search and subsequent autonomously-switched attack run.^[15] In the E configuration, the torpedo was designed to have a total endurance of 20,000 yd (18,000 m) at the 15 knot speed, and 6,000 yd (5,500 m) upon switching to the 24 knot speed.^[16] As of 1958, The E variant was still not ready for service due to problems with its programming, and the prospect of a medium-range ASW torpedo being carried by the upcoming Westland Wasp helicopter was deemed more desirable. As a result, the E variant project was eliminated, leaving only the S variant. 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. As of 1959, the only destroyer class projected to carry the Mark 20 was the Leander,^[17] but as of 1963, this design consideration would also be eliminated.^[18] The final version of the Mark 20 Bidder was also referred to in literature as the Mark 20 Improved.^[19]

The Mark 20 was the only torpedo in service which could fit the short stern launch tubes of the Oberon and Porpoise class submarines. It remained in the submarine service until 1988, which is when the Porpoise class were retired.^[20] Following experience in the 1982 Falklands War, when an armed Mark 20 became stuck inside its tube and HMS Onyx was forced to return to Portsmouth to have it removed, the Oberon class would relegate the stern launch tubes for storing beer, retiring the Mark 20 sooner.^[21]

A project for an autonomous active sonar ASW torpedo to be carried by the Avro Lancaster, Avro Shackleton, Short Sturgeon and Fairey Gannet aircraft in an anti-submarine role, originally conceived in 1947.^[22][23] Development commenced in 1949, and a final design was selected in 1954, delivering functional prototypes with a speed of 30 knots. By this time several of the aircraft capable of carrying a 21-inch torpedo were in the process of being withdrawn from service. Following the 1957 Defence White Paper, which de-emphasized the role of aircraft carriers, the RAF Coastal Command was left as the sole operator and the project was cancelled in 1958 due to cost considerations and an assessment that the weapon lacked the speed to counter upcoming nuclear submarine designs. The seeker head development was transferred to Project Ongar, which would later become the Mark 24 Tigerfish.^[24]

A wire-guided version of the Mark 20 separately developed by Vickers Shipbuilding and Engineering (VSEL) as a private venture. The project was cancelled in 1956, but the wire guidance technology was transferred to the Mark 20 Bidder, contributing to the development of the Mark 23 Grog.^[25]

21-inch Mark 23
A Mark 23 torpedo repainted as an advertisement in front of The Ancient Mariner restaurant in Lynmouth, United Kingdom.
Type	Torpedo
Place of origin	United Kingdom
Service history
In service	1966–1987
Used by	RN
Production history
Designed	1956
Specifications
Mass	2,000 lb (907 kg)
Length	14.9 ft (4.54 m)
Diameter	21 in (530 mm)
Warhead	Torpex
Warhead weight	196 lb (89 kg)
Engine	Electric
Propellant	Battery (perchloric acid)
Operational range	12,000 yd (11,000 m) low-speed, 8,900 yd (8,100 m) high-speed
Maximum speed	20 kn (37 km/h) low-speed, 28 kn (52 km/h) high-speed
Guidance system	Passive Sonar, Wire-Guided

A wire-guided version of the Mark 20 with a dual-speed mode, for target approach and attack run.^[26][27] Wire guidance had been worked on for the Bidder project from its inception, and the earliest prototypes of the Grog were available for testing in 1955. After the Mackle project was cancelled in 1956, the complex wire guidance system was transferred to the Grog program. This would be simplified, improved, and the first production units of the Mark 23 Grog were delivered in 1959.^[28] The Mark 23 was fitted with a 10,000 m (11,000 yd) outboard dispenser that contained a control wire to guide the weapon. Wire guidance was optional, with the control wire spool being a separate module which remained inside the launch tube. An operator onboard the submarine would listen to the torpedo's hydrophones, guiding the weapon past decoys and countermeasures.^[29] Entered service in 1966 although already obsolescent^[30], considering the common speeds of nuclear-propelled submarines of the era. According to one report, the weapon did not become fully operational until 1971^[31], and served until 1987, which is when all stocks of the Mark 24 Tigerfish were converted to Mod 2.

During 1973, all of the RN torpedoes had to be taken out of service as the control system was failing at extreme range.^{[citation needed]}

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

The Mark 24 Tigerfish was a high-speed, long-range, wire-guided torpedo originally developed under Project Ongar. The staff requirement for this weapon was written in 1959^[32] and the weapon was expected to enter service in the mid-1960s, with an in-service target date of 1969.^[33] Initial production rounds were delivered in 1974, and a production order was made in 1977. Affected by the budgetary constraints of the 1966 Defence White Paper, the first Tigerfish (Mod 0) entered deployment in 1983. All variants of the Tigerfish were removed from service in 2004.

The Mark 24 Tigerfish had a protracted development program, beginning with the initial two models, then studies to tackle its deficiencies, and finally a Marconi Consolidation Program (nicknamed "Get Well") undertaken in the late 1980s to convert existing units to the Mod 2 standard.

• Mark 24 Mod 0 Tigerfish (1974)
• Mark 24 Mod 1 Tigerfish (1978)
• Mark 24(N) Tigerfish (nuclear payload variant, paper study only)
• Mark 24 Mod 2 Tigerfish (1987)
• Mark 24 Mod 3 Tigerfish (simplified inexpensive version, paper study only)

Much more capable than Tigerfish. Deployed from 1992, and replacing all Tigerfish by 2004.

• British 18-inch torpedo
• List of torpedoes

• Tony DiGiulian. "British torpedoes Pre World War II".
• Tony DiGiulian. "British Torpedoes of World War II".
• Tony DiGiulian. "British Torpedoes post World War II".
• Post-WWII Whitehead Torpedo and Engineering Works Torpedoes
• Robert Whitehead - A Brief History