There have been a number of 21-inch (53.3 cm) torpedoes in service with the Royal Navy of the United Kingdom. Torpedoes of 21-inch calibre 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 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. Specifications: 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)
Mark II
The Mark II, a prolific series of torpedoes used during the First World War, entered service in 1909. Development ran in parallel with the Mark I and shared multiple elements of its design. Developed by the Royal Navy Torpedo Factory design bureau in Greenock and manufactured at the Royal Gun Factory in Woolwich and the Royal Naval Torpedo Factory in Alexandria. During the early part of the Second World War, 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 First World War, the Mark II was primarily used by battleships and battlecruisers, as well as submarines fitted with 21-inch launch tubes, such as the L, M, and G classes. A wet heater design, it could run at speeds upwards of 45 knots (83 km/h). Accuracy and depth-keeping reliability were reduced at this high speed. All variants of the Mark II were outfitted at the factory with either a 44.5-knot or a 35-knot high speed setting, but not both. The Royal Navy employed a system whereby successive modifications of torpedoes were marked with increasingly numerous asterisks. Other markings for the Mark II were suffixes specifying the type of launch tube hardware required for their employment: SL (side lug), HB (hook bracket), VB (a special modification for the foreign-specification torpedo tubes on HMS Canada, TB (a special modification for the foreign-specification torpedo tubes on HMS Chester (1915) and HMS Birkenhead (1915)) Specifications: Mark II and Mark II SL
Entered service: 1909 Weight: 2,822 lb (1,280 kg) (light warhead), 2,948 lb (1,337 kg) (heavy warhead) Length: 22 ft (6.7 m) Explosive charge: 280 lb (130 kg) or 400 lb (180 kg) TNT Range and speed: 17,000 yd (16,000 m) at 18 kn (33 km/h), 14,000 yd (13,000 m) at 23 kn (43 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 4,200 yd (3,800 m) at 44.5 kn (82.4 km/h) Notes: No submarine variant; compatibility with submarine launch tubes would be developed in successive generations. Mark II HB
Entered service: 1909 Weight: 2,827 lb (1,282 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 10,000 yd (9,100 m) at 28 kn (52 km/h), 4,000 yd (3,700 m) at 44 kn (81 km/h) Notes: The hook bracket variant of the Mark II was actually the first type ordered for production, though it was a modification of the principal design. Mark II*
Entered service: 1914 Weight: 2,948 lb (1,337 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 17,000 yd (16,000 m) at 18 kn (33 km/h), 14,000 yd (13,000 m) at 23 kn (43 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 4,200 yd (3,800 m) at 44.5 kn (82.4 km/h) Mark II** and Mark II** SL
Entered service: 1914 Weight: 2,948 lb (1,337 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 18,000 yd (16,000 m) at 18 kn (33 km/h), 15,000 yd (14,000 m) at 23 kn (43 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 4,500 yd (4,100 m) at 44.5 kn (82.4 km/h) Mark II*** and Mark II*** SL
Entered service: 1914 Weight: 2,948 lb (1,337 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 18,000 yd (16,000 m) at 18 kn (33 km/h), 15,000 yd (14,000 m) at 23 kn (43 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 4,500 yd (4,100 m) at 44.5 kn (82.4 km/h) Notes: In submarine use, the Mark II*** had speed settings of 10,750 yd (9,830 m) at 29 kn (54 km/h) and 4,200 yd (3,800 m) at 45 kn (83 km/h). Mark II*** VB
Entered service: 1914 Weight: 2,865 lb (1,300 kg) Length: 21 ft 4 in (6.50 m) Explosive charge: 302 lb (137 kg) TNT Range and speed: 6,000 yd (5,500 m) at 27 kn (50 km/h), 3,500 yd (3,200 m) at 36 kn (67 km/h), 1,000 yd (910 m) at 41 kn (76 km/h) Notes: Special modification designed to fit foreign-specification launch tubes on HMS Canada. Mark II*** TB
Entered service: 1914 Weight: 2,963 lb (1,344 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 10,000 yd (9,100 m) at 28 kn (52 km/h), 4,000 yd (3,700 m) at 44 kn (81 km/h) Notes: Special modification designed to fit foreign-specification launch tubes on HMS Chester (1915) and HMS Birkenhead (1915). Mark II****
Entered service: 1915 Weight: 2,950 lb (1,340 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 18,000 yd (16,000 m) at 18 kn (33 km/h), 15,000 yd (14,000 m) at 23 kn (43 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 4,500 yd (4,100 m) at 44.5 kn (82.4 km/h) Notes: In submarine use, the Mark II**** had speed settings of 10,750 yd (9,830 m) at 29 kn (54 km/h) and 4,200 yd (3,800 m) at 45 kn (83 km/h). Mark II*****
Entered service: 1916 Weight: 2,953 lb (1,339 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 18,000 yd (16,000 m) at 19 kn (35 km/h), 15,000 yd (14,000 m) at 24 kn (44 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 4,500 yd (4,100 m) at 45 kn (83 km/h) Notes: In submarine use, the Mark II***** had speed settings of 10,750 yd (9,830 m) at 29 kn (54 km/h) and 4,200 yd (3,800 m) at 45 kn (83 km/h).
== Mark III == The 21-inch Mark III designation was applied to two separate torpedoes. One was the RGF Mark III, manufactured at the Royal Gun Factory in Woolwich. The RGF Mark III incorporated features of the RGF Mark II***, as well as a novel design for the water bottle, a different gas generator, a double reducer adapted for the use of heavy fuel oil, and a direct oil injection system which was projected to increase the weapon's endurance to 13,000 yd (12,000 m). This was not realized, causing the weapon's introduction to be indefinitely postponed, favor being passed on to improved variants of the Mark II. The other was the Whitehead Mark III produced at the Whitehead factory in Weymouth, a torpedo produced for foreign export in two variants, the Mark III and Mark III*. Both variants were propelled by four-cylinder engines. At the outbreak of the First World War, the Royal Navy purchased and introduced into service all stocks of Whitehead Mark II and Mark III foreign export torpedoes present at the Weymouth works. Specifications: RGF Mark III
Prototype date: 1915 Weight: 2,815 lb (1,277 kg) Length: 22 ft (6.7 m) Explosive charge: 400 lb (180 kg) TNT Range and speed: 11,700 yd (10,700 m) at 29 kn (54 km/h) Whitehead Mark III
Entered service: 1914 Weight: 2,697 lb (1,223 kg) Length: 20 ft 10 in (6.35 m) Explosive charge: 300 lb (140 kg) TNT Range and speed: 6,000 yd (5,500 m) at 27 kn (50 km/h), 3,500 yd (3,200 m) at 36 kn (67 km/h), 1,000 yd (910 m) at 41 kn (76 km/h) Notes: Maximal range of 10,000 yd (9,100 m) at an unknown speed. Whitehead Mark III*
Entered service: 1914 Weight: 2,912 lb (1,321 kg) Length: 22 ft 4 in (6.81 m) Explosive charge: 330 lb (150 kg) TNT Range and speed: 10,000 yd (9,100 m) at 25 kn (46 km/h), 3,500 yd (3,200 m) at 38 kn (70 km/h) Notes: Maximal range of 12,000 yd (11,000 m) at an unknown speed.
Mark IV
The Mark IV torpedo was the principal British torpedo of World War I. Designed 1912, initially available 1915, adopted for service 1916. 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. Specifications: Mark IV
Entered service: 1916 Weight: Approximately 3,100–3,200 lb (1,400–1,500 kg) Length: 22 ft 2.5 in (6.769 m) to 22 ft 5 in (6.83 m) Explosive charge: 400 or 500 lb (180 or 230 kg) TNT Range and speed: 4,500 yd (4,100 m) at 44.5 kn (82.4 km/h), 15,000 yd (14,000 m) at 25 kn (46 km/h), 18,000 yd (16,000 m) at 21 kn (39 km/h) Notes: Two warhead options were available, the IVa (400 lbs) and the IVb (500 lbs). Depth keeping was extremely unreliable at the 44.5-knot speed setting, prompting a suggestion to limit the top speed to 35 knots. Mark IV*
Entered service: 1917 Weight: Approximately 3,100–3,200 lb (1,400–1,500 kg) Length: 22 ft 2.5 in (6.769 m) to 22 ft 5 in (6.83 m) Explosive charge: 400 or 500 lb (180 or 230 kg) TNT Range and speed: 4,500 yd (4,100 m) at 44.5 kn (82.4 km/h), 6,000 yd (5,500 m) at 35 kn (65 km/h), 11,000 yd (10,000 m) at 29 kn (54 km/h), 15,000 yd (14,000 m) at 25 kn (46 km/h), 18,000 yd (16,000 m) at 21 kn (39 km/h) Notes: Four speed settings and an improved gyro control gear. The Mark IV* was outfitted at the factory with either a 44.5-knot or a 35-knot high speed setting, but not both. Mark IV Late
Entered service: Circa 1930s Weight: 3,206 lb (1,454 kg) Length: 22 ft 7.5 in (6.896 m) Explosive charge: 515 lb (234 kg) TNT Range and speed (surface vessel variant): 8,000 yd (7,300 m) at 35 kn (65 km/h), 10,000 yd (9,100 m) at 29 kn (54 km/h), 13,500 yd (12,300 m) at 25 kn (46 km/h) Range and speed (submarine variant): 6,000 yd (5,500 m) at 40 kn (74 km/h), 9,500 yd (8,700 m) at 30 kn (56 km/h) Notes: Retrofitted older torpedoes in service during the Second World War. Issued to older warships and motor torpedo boats equipped with 21-inch launch tubes, as well as submarines.
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 1922, originally for the County-class cruisers that were built 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 VII would be replaced by the Mark IX as opportunity offered. Specifications: Mark VII
Entered service: 1925 Propulsion: Wet heater (kerosene-air, oxygen enriched) Weight: 4,106 lb (1,862 kg) Length: 25 ft 6 in (7.77 m) Explosive charge: 740 lb (340 kg) TNT Range and speed: 16,000 yd (15,000 m) at 33 kn (61 km/h) Mark VIIC
Entered service: 1939 Propulsion: Wet heater (shale oil-air) Weight: 4,106 lb (1,862 kg) Length: 25 ft 6 in (7.77 m) Explosive charge: 740 lb (340 kg) TNT Range and speed: 5,700 yd (5,200 m) at 35 kn (65 km/h) Notes: Designated "C" for "Converted". Remnant stocks were refurbished at the outbreak of war in 1939. Conventional compressed air oxidizer, shale oil reactant. A mere nine units of the Mark VIIC were expended during 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 class, as well as motor torpedo boats. The principal World War II version was the improved Mark VIII**, used far more than any other torpedo in service, with 3,732 being expended by September 1944 (56.4% of the total number of torpedoes used by Britain during the war). In 1950–1951, the only system available for a Royal Navy submarine to attack another submerged target was the Mark VIII; active homing variants of the Mark VIII and Mark IX were being worked on in 1945, without success. Considerable self-noise and reverberation hampered the effort, and the project was halted with funding being cut off as the war ended. During trials, the Mark VIII achieved a test depth of 200 ft (61 m) without problems, but the production units were limited to a maximal depth of 44 ft (13 m) by their depth control mechanisms. At the beginning of the 1960s, the Mark VIII was the only feasibly effective anti-surface ship weapon available to the Royal Navy submarine service. The Mark 20 Bidder, while capable of hitting surface targets, lacked the speed to chase down warships. During the torpedo capability crisis, in 1969, Admiral Michael Pollock, Flag Officer Submarines, proposed several possible solutions. Proposals included purchase of the American Mark 45 ASTOR, the Mark 40 Mod 1 nuclear-armed lightweight torpedo, the UUM-44 SUBROC, or modification of the Mark VIII to be fitted with a WE177A nuclear warhead, with a variable yield of 0.5-10 kilotons. The torpedo remained in service with the Royal Navy in a training role until the 1990s, and was used by the Royal Norwegian Navy (Coastal Artillery: Kaholmen torpedo battery at Oscarsborg Fortress) until 1993. Specifications: Mark VIII
Entered service: 1927 Weight: 3,452 lb (1,566 kg) Length: 21 ft 7 in (6.58 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* and Mark VIII*E
Entered service: 1936 Explosive charge: 722 lb (327 kg) Torpex Range and speed: 7,000 yd (6,400 m) at 41 kn (76 km/h) (Mark VIII*); 6,400 yd (5,900 m) at 41 kn (76 km/h) (Mark VIII*E) Notes: Mark VIII*E was a variant for externally-mounted torpedo tubes, with smaller propellers; this variant continued to be produced throughout the war. The Mark VIII*E was also compatible with internal launch tubes. Mark VIII**
Entered service: 1940 Explosive charge: 722 lb (327 kg) Torpex, later increased to 805 lb (365 kg) Torpex Max depth setting: 44 ft (13 m) 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) (light warhead); 4,570 yd (4,180 m) at 45.5 kn (84.3 km/h), 6,400 yd (5,900 m) at 41 kn (76 km/h) (heavy warhead) Notes: Most prolific British torpedo during the Second World War. Predominantly fitted with the heavy warhead. Mark VIII***
Entered service: 1960 Weight: 3,384 lb (1,535 kg) Length: 22 ft (6.7 m) Explosive charge: 805 lb (365 kg) Torpex Max depth setting: 60 ft (18 m) 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) Notes: First postwar modernization and service life extension. Speeds were slightly reduced in exchange for greatly increased accuracy, reliability, and range. Mark 8 Mod 4
Entered service: 1965 Notes: Final modernization and service life extension. The policy of denoting successive modifications with increasingly numerous asterisks was finally ended. A Mark 8 Mod 4 was the very last torpedo to be launched at the Arrochar torpedo range, on 19 March 1986. 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 Mod 4 torpedoes during the Falklands War. This is the first sinking of a surface ship by a nuclear-powered submarine in wartime and the second (of four) sinkings of a surface ship by any submarine since the end of World War II. The other three sinkings were of the Indian frigate INS Khukri, the South Korean corvette ROKS Cheonan and the Iranian frigate IRIS Dena.
