There have been several British 21-inch diameter 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, and "Long" at 23 ft 1.25 in. 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 Town-class destroyers provided to the UK during the early part of the Second World War. The running speed was reduced from 45 knots for better reliability. The Mark II*, an improved Mark II was used by battleships and battlecruisers. Awet heater design, it could run for at.
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.
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 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.
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. The torpedo is still in service with the Royal Navy albeit in a limited role, and with the Royal Norwegian Navy 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.
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" cruisers during the war.
Mark X
From 1939, used by submarines, motor torpedo boats and destroyers from other navies such as the Grom.
Mark XI
Electric battery powered torpedo with a TNT warhead. Entering service during the Second World War it was used by destroyers.
At first codenamed Ferry, then Fancy, the Mark 12 never reached production. From 1952, it had a warhead of Torpex. Using high test peroxide fuel, it attained a top speed of for. 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
Developed under the codename "Bidder", the Mark 20 was a passive-seeker battery-powered torpedo for use by surface ships and submarines. 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 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. It was cancelled after protracted work but the seeker development was used in Tigerfish.
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 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.
The first Tigerfish 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.
