British 21 inch torpedo

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
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 at 45 kn

21 inch 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 (51).

21 inch Mark V
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
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 s 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
Specifications: Mark VIII
 * Entered Service: 1927
 * Weight: 3,452 lb (1,566 kg)
 * Length: 259 in (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 (S48) sank the Argentine cruiser ARA General Belgrano with three Mark VIII** torpedoes during the Falklands War. 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 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 Torpex. Powered by high test peroxide, giving it a speed of 28 kn for 5 km.

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.

21 inch 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 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. 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