Royal Ordnance L11A5
Encyclopedia
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.
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 The weapon has been superseded by the L30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.
designed a new 120mm rifled tank gun in 1957. The new gun was deemed to be necessary because the British Army
specified engagement range
s greater than those of other armies, for example 2000 m (2,187.2 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. 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.
. The gun was equipped with a hydro-pneumatic recoil system using two buffers. The gun recoil
s 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 2600 metres (2,843.4 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.
Tank gun
A tank gun is the main armament of a tank. Modern tank guns are large-caliber high-velocity guns, capable of firing kinetic energy penetrators, high explosive anti-tank rounds, and in some cases guided missiles. Anti-aircraft guns can also be mounted to tanks.-Overview:Tank guns are a specific...
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
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
. A total of 3,012 L11 guns were produced at a reported unit cost of US $227,000.
The L11 was developed by Britain's Royal Ordnance Factories to equip the Chieftain tank
Chieftain tank
The FV 4201 Chieftain was the main battle tank of the United Kingdom during the 1960s and 1970s. It was one of the most advanced tanks of its era, and at the time of its introduction in 1966 had the most powerful main gun and heaviest armour of any tank in the world...
as the successor to the L7
Royal Ordnance L7
The Royal Ordnance L7 is the basic model of Britain's most successful tank gun. The L7 was a 105 mm L/52 rifled design intended for use in armoured fighting vehicles...
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
L30
The L30 is a 120mm tank gun used by the British Army and Royal Army of Oman. It is fitted in the turret of the Challenger 2 main battle tank. It is an improved production model of the Royal Ordnance L11 series of rifled tank guns.-Challenger Armament:...
series 120 mm rifled tank gun.
History
The Royal Armament Research and Development Establishment at Fort HalsteadFort Halstead
Fort Halstead is a research site of Dstl, an Executive Agency of the UK Ministry of Defence. It is situated on the crest of the Kentish North Downs, overlooking the town of Sevenoaks...
designed a new 120mm rifled tank gun in 1957. The new gun was deemed to be necessary because the British Army
British Army
The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...
specified engagement range
Range of a projectile
right|thumb|250 px|The path of this projectile launched from a height y0 has a range d.In physics, assuming a flat Earth with a uniform gravity field, a projectile launched with specific initial conditions will have a predictable range. As in Trajectory of a projectile, we will use:The following...
s greater than those of other armies, for example 2000 m (2,187.2 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. 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:
- Rifled tank guns can (in addition to firing conventional spin-stabilized ammunition) fire fin stabilized ammunition by using a slipping driving band. This allows employment of the widest range of ammunition.
- Spin-stabilized ammunition, as fired from rifledRiflingRifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...
tank guns, has inherent advantages of stability in flight. - A rifled piece is more economical to procure and maintain.
Since its introduction, the L11 has evolved into eight production versions. In June 1976 development of new ammunition for the L11A5 was begun.
Production Models
Royal Ordnance basic L11 design was developed into a series of improved production models; the :L11A5 being the major production version.- L11A1 – The initial production variant; 130 produced.
- L11A2 –RO Defence incorporated numerous minor changes, including a modified vent tube, an obturator sleeve protector, and a 15-hole vent tube magazine. Stronger material was used in fabricating the breech ring.
- L11A3 – This incorporated minor changes to the breech ring.
- L11A4 –Evaluation test prototype for an automatic loading system.
- L11A5 – This was the main production model. It introduced the integral muzzle reference system and a smaller and lighter fume extractor which required the addition of 7.7 kilograms (17 lb) of weight at the breech for balance.
- L11A6 – This was a conversion of the A3 to accommodate the muzzle reference system and fume extractor of the A5.
- L11A7 – A semi-automatic plunger was proposed for the vent tube loader, but did not enter production.
- L30L30The L30 is a 120mm tank gun used by the British Army and Royal Army of Oman. It is fitted in the turret of the Challenger 2 main battle tank. It is an improved production model of the Royal Ordnance L11 series of rifled tank guns.-Challenger Armament:...
(EXP 32M1) – The latest variant of the L11 design, developed under the Challenger Armament program.
Technology
The breech mechanism is a downward sliding semi-automatic breechblockBreechblock
A breechblock is the part of the firearm action that closes the breech of a weapon at the moment of firing....
. The gun was equipped with a hydro-pneumatic recoil system using two buffers. The gun recoil
Recoil
Recoil is the backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile and exhaust gasses, according to Newton's third law...
s 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
Bore evacuator
A bore evacuator is a device on the gun barrel of an armoured fighting vehicle which helps prevent poisonous propellant gases from venting back into the vehicle's fighting compartment when the gun breech is opened to load another round. Bore evacuators are most often used on large-calibre tank...
approximately two-thirds of the way to the muzzle and a thermal sleeve
Thermal sleeve
A thermal sleeve is a device around the length of a gun barrel of a large caliber gun, typically found on modern tanks. Its primary purpose is to prevent the gun barrel from being thermally distorted due to environmental conditions, especially when the barrel is already hot due to frequent...
.
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 2600 metres (2,843.4 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.
Specification
- Caliber: 120 millimetres (4.7 in)
- Barrel length 6.604 metres (21.7 ft) (55 cal)
- Length overall 6.858 metres (22.5 ft)
- Weight: 1778 kilograms (3,919.8 lb)
- Recoil Length 37 centimetres (1.2 ft)
- Maximum range (APDS) 3000 metres (3,280.8 yd)
- Maximum range (HESH) 8000 metres (8,748.9 yd)
- Maximum rate of fire 10 rounds/min
- Sustained rate of fire 6 rounds/min
Available Ammunition
- L31 High Explosive Squash Head (HESH)
- L15 Armour Piercing Discarding Sabot-Tracer (APDS-T)
- L20 Discarding Sabot-Tracer (DS-T)
- L23 Armour Piercing Fin Stabilized Discarding Sabot (APFSDS)
- L34 Smoke
- L32 Squash Head-Practice (SH-P)
- L35A1 canister shotCanister shotCanister shot is a kind of anti-personnel ammunition used in cannons. It was similar to the naval grapeshot, but fired smaller and more numerous balls, which did not have to punch through the wooden hull of a ship...