| L11A5 | |
|---|---|
Gun on Challenger 1 tank at Bovington Tank Museum, UK, 2010 |
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| Service history | |
| In service | 1966- |
| Used by | UK, Iran, Jordan |
| Production history | |
| Designer | Royal Armament Research and Development Establishment |
| Designed | 1957 |
| Manufacturer | Royal Ordnance Factories |
| Number built | 3,102 |
| Specifications | |
| Weight | 1,778 kilograms (3,920 lb) |
| Length | 6.858 metres (22.50 ft) |
| Barrel length | 55 calibres |
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| Shell | bagged charge |
| Calibre | 120 mm |
| Rate of fire | 6-10 rounds per minute |
The Royal Ordnance L11A5 is a 120 mm L/55 rifled tank gun design. It was the first of NATO's 120mm tank guns which became the standard calibre for Western tanks in the later period of the Cold War. A total of 3,012 L11 guns were produced at a reported unit cost of US $227,000.[1]
The L11 was developed by Britain's Royal Ordnance Factories to equip the Chieftain tank as the successor to the L7 gun used in the Centurion tank. It was also used on the Challenger 1, which replaced the Chieftain in British and Jordanian service. The weapon has been superseded by the L30 series 120 mm rifled tank gun.
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The Royal Armament Research and Development Establishment at Fort Halstead designed a new 120mm rifled tank gun in 1957. The new gun was deemed to be necessary because the British Army specified engagement ranges greater than those of other armies, for example 2,000 m (2,200 yd), as specified by the US Army, despite studies at the time that suggested engagement ranges were below those of the US Army requirements in the great majority of cases.[2] The L11 was specifically designed to fit into the turret mountings of the Chieftain tank (FV4201). After firing trials in 1961, the L11 was accepted for service on the Chieftain in 1965, and entered service with the British Army in 1966.
The British Army defended their decision to adopt a rifled gun as opposed to a smooth-bore which other NATO nations favoured by arguing that:
Since its introduction, the L11 has evolved into eight production versions. In June 1976 development of new ammunition for the L11A5 was begun.
Royal Ordnance basic L11 design was developed into a series of improved production models; the :L11A5 being the major production version.
The breech mechanism is a downward sliding semi-automatic breechblock. The gun was equipped with a hydro-pneumatic recoil system using two buffers. The gun recoils 37 cm (in most applications).
Unlike most tank weapons which fire a single fixed round, the round (projectile) and propellant are loaded separately. The propellant is in the form of a combustible "bag" charge (or later, a combustible charge case for armour-piercing rounds). This required the obturation to be provided by the breech rather than the cartridge case, as is the case in fixed rounds. When first introduced, APDS (armour-piercing) rounds were fired using a cylindrical charge. High explosive squash head (HESH), smoke and other rounds used a hemi-cylindrical (i.e. a cylinder sliced in two lengthways) charge (the L3). Two HE charges could therefore be stowed in the same space as one AP charge. In the Chieftain and Challenger tanks, the charges were stored in 36 recesses surrounded by water jackets, so that a hit which penetrated the fighting compartment would rupture the jacket and drench the propellant, preventing a catastrophic ammunition fire, or "brew-up".
The barrel of the L11A5 is fitted with a bore evacuator approximately two-thirds of the way to the muzzle and a thermal sleeve.
When first introduced, a .50 calibre ranging gun was fitted over the barrel of the L11. The projectiles for this ballistically matched those for the main armament out to 2,600 metres (2,800 yd), at which point the tracer element burned out. This effectively limited the maximum range for the main gun to this distance. In the late 1970s, laser rangefinders replaced the ranging MG in British service, allowing engagements at longer ranges.