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.

Mark I
The first British 21-inch torpedo came in two lengths, "Short" at 17 ft, and "Long" at 23 ft. The explosive charge was 200 lb of gun cotton, increased later to 225 lb.

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 (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 4100 m at 45 kn.

Mark IV
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 (51).

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 VIII
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.

Specifications:

Mark VIII Mark VIII**
 * Entered service: 1927
 * Weight: 3452 lb
 * Length: 259 in
 * Explosive charge: 750 lb TNT
 * Range and speed: 5000 yd at 40 kn
 * Explosive charge: 722 lb Torpex, later increased to 805 lb Torpex
 * Range and speed: 5000 yd at 45.6 kn, 7000 yd at 41 kn

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 (S48) sank the Argentine cruiser ARA General Belgrano with two Mark VIII** torpedoes during the Falklands War. 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 (F149) and the South Korean corvette ROKS Cheonan.

Mark IX
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 gun cruisers during the war. The Mark IX torpedo remained in service throughout the 1960s.

Specifications:

Mark IX Mark IX* Mark IX**
 * Entered service: 1930
 * Weight: 3732 lb
 * Length: 286.5 in
 * Explosive charge: 750 lb TNT
 * Range and speed: 10500 yd at 36 kn, 13500 yd at 30 kn
 * Explosive charge: 805 lb Torpex
 * Range and speed: 11000 yd at 36 kn, 14000 yd at 30 kn
 * Explosive charge: 805 lb Torpex
 * Range and speed: 11000 yd at 41 kn, 15000 yd at 35 kn

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 322 kg TNT warhead. It entered service during the Second World War and 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 340 kg Torpex. Using high test peroxide fuel, it attained a top speed of 28 kn for 5000 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.

Mark 20 Bidder
The Mark 20 was a passive-seeker battery-powered torpedo which was developed alongside the 18-inch Mark 30 Dealer B and shared elements of its design. 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. In the E configuration, the torpedo was designed to have a total endurance of 20000 yd at the 15 knot speed, and 6000 yd upon switching to the 24 knot speed. 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, but as of 1963, this design consideration would also be eliminated. The final version of the Mark 20 Bidder was also referred to in literature as the Mark 20 Improved.

It remained in the submarine service until the 1980s, whereupon it was replaced by the Mark 24 Tigerfish.

Mark 21 Pentane
A project for an autonomous active/passive sonar ASW torpedo to be carried by the Short Sturgeon and Fairey Gannet anti-submarine aircraft. Development commenced in 1949 and delivered functional prototypes with a speed of 30 knots. 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. The seeker head development was transferred to Project Ongar, which would later become the Mark 24 Tigerfish.

Mark 22 Mackle
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.

Mark 23 Grog
A wire-guided version of the Mark 20 with a dual-speed mode, for target approach and attack run. The Mark 23 was fitted with a 10000 m outboard dispenser that contained a control wire to guide the weapon. Entered service in 1966 although already obsolescent, and did not become fully operational until 1971, serving only as an interim before the Mark 24 Tigerfish entered service.

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 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.

Mark 24 Tigerfish
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 and the weapon was expected to enter service in the mid-1960s, with an in-service target date of 1969. 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)

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