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Royal Ordnance L7

The Royal Ordnance L7 is the basic model of the United Kingdom's most successful tank gun. The L7 is a 105 mm L/52 rifled design by the Royal Ordnance Factories intended for use in armoured fighting vehicles, replacing the earlier 20-pounder (84 mm) tank gun mounted on the Centurion tank.[1] The successful L7 gun has been fitted on many armored vehicles including the British Centurion (starting from the Mk. 5/2 variant), the German Leopard 1 and early variants of the US M1 Abrams (M1 and M1IP).

Royal Ordnance L7
M1 Abrams 1981 Gunner and Coax M240.jpg
The M68A1 105mm gun, the US version of the L7, mounted on an M1 Abrams
TypeRifled Tank gun
Place of originUnited Kingdom
Production history
ManufacturerRoyal Ordnance Factory
BAE Systems
Specifications
Mass1,282 kg (2,826 lb)
Length5.89 m (19.3 ft)
Barrel length52 calibres (5.46 m or 17.9 ft)

Calibre105 mm (4.13 in)
Rate of fire10 rounds per minute (maximum)
Maximum firing range4000 m (13,123 ft)

The L7 is a popular weapon and continued in use even after it was superseded by the L11 series 120 mm rifled tank gun, for some Centurion tanks operating as Artillery Forward Observation and Armoured Vehicle, Royal Engineers (AVRE) vehicles. The L7, and adaptations of it, can be found as standard or retrofitted equipment on a wide variety of tanks developed during the Cold War.

HistoryEdit

 
L7 105 mm tank gun cut model on display at the Deutsches Panzermuseum.

Work on what became the L7 began in the early 1950s under Armament Research and Development Establishment at Fort Halstead with the first gun trials in mid-1956.[2] Later that year during the Hungarian Revolution of 1956, a Soviet T-54A medium tank was driven onto the grounds of the British embassy in Budapest by the Hungarians. After a brief examination of this tank's armour and 100 mm gun, British officials decided that the 20 pounder was apparently incapable of defeating it. Hence there was a need to adopt a 105 mm gun.[3]

The L7 was specifically designed to fit into the turret mountings of the 20 pounder. This would enable the Centurion tanks to be up-gunned with minimum modifications; hence, the fleet could be upgraded in a shorter time and at a lower cost.

User trials of the weapon began in 1959. The first tank to be equipped with the L7 was a single up-armoured Centurion Mark 7 in 1959 which was to prove the viability of up-armouring and up-gunning the Centurion. From 1959 onwards existing Centurions were given upgrades with the L7 gun and armour and new builds incorporated the L7 at production.[4] The gun was subsequently adopted by the German Leopard 1 (for which the L7A3 variant was developed).

The United States M60 series and earliest versions of the M1 Abrams tanks are armed with the M68 gun, which is a licensed built variant of the L7.[5] The M68 is also featured on the early Israeli Merkava. The Swedish Stridsvagn 103 turretless S-tank (armed with the Bofors L74 with an automatic loader) makes use of an indigenous gun design, which is compatible with rounds made for the L7. In addition, several countries have used the gun to improve the firepower of existing main battle tanks. Derivatives have even been mounted in Warsaw Pact-built T-54 and T-55 tanks in Israel, India, Egypt and Iraq, and Type 79 tanks in China.

DesignEdit

The breech uses a horizontally sliding breechblock for loading the fixed cartridge cases. The gun recoils approximately 29 cm (11.5 inch) (in most applications), automatically opening the breech and ejecting the empty cartridge case as the gun returns to battery from full recoil. The barrel of the L7 is fitted with a bore evacuator approximately halfway down its length. The extractor is eccentrically mounted, which allows the gun to be depressed over the vehicle's engine deck. This is a key recognition feature, since its successor, the L11 rifled tank gun also features a cylindrical concentric extractor.

SpecificationEdit

  • Calibre: 105 mm (4.13 in)
  • Cartridge: 105×607 mm R, 105×617 mm R
  • Barrel length: 52 calibres (218.5 inches)[6]
  • Weight: 1,282 kg (2,826 lb)
  • Length: 5.89 m (19 ft 4 in)
  • Rate of fire: 10 rounds per minute (maximum)
  • Range: 4,000 meters[7]

AmmunitionEdit

Kinetic energy projectiles[8][9][10][11]

Ammunition Origin Type* Penetrator material Muzzle velocity (m/s) Projectile mass (kg) RHA penetration (mm) Notes
L28 & L36 (M392) United Kingdom APDS-T Tungsten 1478 5.8 120 mm @ 60° at 914 m
L52 (M728) United Kingdom APDS-T Tungsten 1426 120 mm @ 60° at 1828 m
M735 United States APFSDS-T Tungsten 1501 5.8
M774 United States APFSDS-T Depleted Uranium 1508
M833 United States APFSDS-T Depleted uranium 1493
M900 United States APFSDS-T Depleted uranium 1505 Cannot be fired by M68 only M68A1
M111 Israel APFSDS-T Tungsten 4.2 Israeli round nicknamed "Hetz"
DM23 West Germany APFSDS-T Tungsten 4.2 German licensed copy of M111

Chemical energy projectiles

Ammunition Origin Type* Muzzle velocity (m/s) Projectile mass (kg) RHA penetration (mm) Notes
M456 United States HEAT-FS 1173 10.2 400 Used Composition B as explosive
M393 United States HEP 732 11.3

*-T designation refers to the round containing a tracer element.

**known as HEP (High Explosive Plastic) in the United States

VariantsEdit

  • L7A1
Standard UK production variant.
  • L7A3
Variant for the (West) German Leopard 1 MBT. The upper rear corner of the breech block reduced in size so gun can be depressed without hitting the turret roof.
  • T254E1
US designation for the L7A1. It had the same horizontal sliding breach block as the L7 and used British X15/L52 tubes with a concentric bore evacuator on the barrel.
  • T254E2
United States variant of the T254. It had a vertical sliding breach block with the X15E8 tube and a concentric bore evacuator. Standardized as the M68E1. Used in M60 Patton prototype vehicles.
  • T254E3
US variant. Same as the T254E2 but with chrome plated bores. Only 2 built. [12]
  • M68E1
United States built gun for the M60 Patton series and early XM1 Abrams. Initially designated T254E2, it is a variant of the indigenous U.S. 105mm T254. Unlike the 105mm T254E2, its XM24E1/L52 tube had an eccentric bore evacuator which was interchangeable with that of the British X15E8/L52 tube.[5] Used on Israeli tanks up until the Merkava III.
  • M68A1E2
In March 1983, a program was initiated to develop an enhanced version of the 105mm gun. The new XM24[13] gun tube was extended by 1.5 meters compared to the M68A1 and it could tolerate a higher chamber pressure. Designed to replace the 105mm gun M68A1 in the Ml and the IPM1, it was expected to have improved penetration performance, particularly with the upcoming M900 APFSDS. At that time, it was expected that the installation of the enhanced 105mm gun would be a less costly method of upgrading the tank's firepower compared to retrofitting the Ml and IPM1 with the 120mm gun M256. Later, the enhanced 105mm gun was abandoned[14] and the 120mm gun was selected for retrofitting in the earlier models of the Abrams.
  • M68A2E4
Variant of the US M68 designed for use on the Stryker MGS, fitted with an automatic loader.
  • KM68A1
The South Korean Army's licence-produced variant of the US M68 gun. Used on the South Korean variant of the M48, the M48A5K and K1 tanks.
  • M68T
Turkish licence-built versions by MKEK under the designation of M68T to up-gun its 90mm armed M48 fleet, took place in the 1980s.
  • Type 79/81/81A/83
Chinese produced L7. Licence procured from Austria.
  • FM K.4 Modelo 1L
Argentine Army's licence produced by Fabricaciones Militares in Argentina. Used on the TAM medium tank.
South African built variant for the Olifant Mk1A and Rooikat 105. Incorporates a heavily modified recoil assembly.

UsageEdit

L7 variantEdit

M68 variantEdit

  • K1 Type 88: KM68A1 cannon
  • Merkava: Mark I and Mark II models
  • T-54/55: in some upgraded variants
    • Tiran-4Sh: Israeli modification of T-54, both L7 and M68 variants fitted
    • Tiran-5Sh: Israeli modification of T-55, both L7 and M68 variants fitted
    • Ramses II: Egyptian T-55 modernization.

Related Designs with Compatible AmmunitionEdit

NotesEdit

  1. ^ Starry, p. 113
  2. ^ Dunstan Centurion Tank: 1943-2003 Osprey Publishing p23-24
  3. ^ Zaloga 2004, pp 13, 39.
  4. ^ Dunstan p24
  5. ^ a b Hunnicutt, R.P. (1984). Patton: A History of the American MBT. Presidio. p. 152.
  6. ^ http://www.williammaloney.com/Aviation/WatervlietArsenalMuseum/TankCannon/pages/09M68_105mmGun.htm
  7. ^ http://www.williammaloney.com/Aviation/WatervlietArsenalMuseum/TankCannon/pages/09M68_105mmGun.htm
  8. ^ Hunnicutt, R.P. (1990). Abrams: A History of the American Main Battle Tank. Presidio. p. 312. ISBN 978-1626541665.
  9. ^ "ARMY AMMUNITION DATA SHEETS ARTILLERY AMMUNITION GUNS, HOWITZERS, MORTARS, RECOILLESS RIFLES, GRENADE LAUNCHERS, AND ARTILLERY FUZES (FSC 1310, 1315, 1320, 1390)" (PDF). Bullet Picker. April 1994. Archived (PDF) from the original on 2019-02-28. Retrieved 2019-02-27.
  10. ^ Projectile and Warhead Identification Guide—Foreign NGIC-1143-782-98
  11. ^ FM 3-20.12 TANK GUNNERY (ABRAMS)
  12. ^ Hunnicutt, R. P. "Patton: A History of the American Main Battle Tank." 1984; Presidio Press. ISBN 0-89141-230-1 p.119
  13. ^ "M60A3 Patton Tank Thermal Sight (TTS)". www.globalsecurity.org.
  14. ^ Hunnicutt, R.P. (1990). Abrams: A History of the American Main Battle Tank. Presidio. p. 202. ISBN 9780891413882.
  15. ^ "M60 Patton Series - Globalsecurity.org". Archived from the original on 2008-12-02. Retrieved 2008-12-02.

ReferencesEdit

  • Zaloga, Steven J. and Hugh Johnson (2004). T-54 and T-55 Main Battle Tanks 1944–2004. Oxford: Osprey. ISBN 1-84176-792-1.
  • Starry, Donn A., General. "Mounted Combat In Vietnam." Vietnam Studies. Department of the Army. First printing 1978.
  • Hunnicutt, R. P. "Patton: A History of the American Main Battle Tank." 1984; Presidio Press. ISBN 0-89141-230-1.