Royal Ordnance L7


The Royal Ordnance L7, officially designated Gun, 105 mm, Tank, 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 tank gun mounted on the Centurion tank. The successful L7 gun has been fitted on many armored vehicles including the British Centurion, the German Leopard 1 and early variants of the US M1 Abrams.
The L7 is a popular weapon and continued in use even after it was superseded by the L11 series 120 mm rifled tank gun, for some Centurion tanks operating as Artillery Forward Observation and Armoured Vehicle, Royal Engineers vehicles.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.

History

Both the United Kingdom and the United States had been developing projects for large calibered guns during WWII in order to compete with increasingly heavily armored German tanks, and later for Cold War Soviet tanks. The US developed several heavy tank designs during this period, notable were the US 105 mm Gun T5 as well as the British A39 Tortoise heavy tanks.
The US foresaw difficulties in engagements against the Soviet IS-3 and 4 with its M48 Patton. This led to the introduction of the M103, a heavy tank designed to counter Soviet heavy tanks. It mounted an extremely powerful 120 mm cannon but the ammunition was so large that it required two loaders, one for the shell and another for the separate propellant charge. Of the 300 M103s built, most went to the Marines. The UK came to the same conclusions and developed their own heavy tank, the Conqueror, which mounted the US 120 mm gun.

United Kingdom

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 armor and 100 mm gun, British officials decided that the 20 pounder was apparently incapable of defeating its frontal armor. This meant the most common British tanks were no longer able to deal with Soviet medium tank designs, let alone their heavy tanks.
These events spurred the United Kingdom to develop a new tank gun in 1956, the Royal Ordnance L7 to keep the Centurion viable against this new Soviet tank design and the United States to develop the XM60 tank in 1957. 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.

United States

The main gun for the M60 tank series was chosen after a comparative firing test of six different guns carried out on the Aberdeen Proving Grounds in 1958. The factors evaluated were accuracy, the lethality of a hit, rate of fire, and penetration performance. Based on these tests, the 105 mm T254E1 was selected, modified to the T254E2 and standardized as the Cannon, 105-MM Gun, M68. They are licensed built US variants of the L7. The T254E2/M68 used a vertical sliding breechblock instead of the T254E1's horizontal breechblock. Until American-made barrels could be obtained with comparable accuracy, British X15/L52 barrels mounting a concentric bore evacuator on the barrel were to be used. US built XM24/L52 barrels fitted with an eccentric bore evacuator were used for the M60-series starting in June 1959 but retained interchangeability with the British X15/L52 barrel. All of the US guns and XM24 barrels were produced at the Watervliet Arsenal, NY and the gun mounts manufactured at the Rock Island Arsenal, IL. US M68 guns were fitted with an eccentric bore evacuator instead of a concentric model in order to provide more clearance over the rear deck of the tank. The original variant of the M60 tank was equipped with the M68 gun using the M116 mount. Additionally, many M48A3s armed with a 90mm gun that were in NG-CONUS service with the Army National Guard were retrofitted with the M68 gun and redesignated as the M48A5. This was done to maintain training levels of Guard units as well as using a commonality in ammunition amongst tanks.
The M60A1 and A3 variants of the M60 series and earliest pre-production XM1 prototypes of the M1 Abrams tanks are armed with the M68E1 variant of the gun. The M68E1 gun shares the same firing characteristics as the M68. It featured several design improvements including an updated gun hydraulic configuration, a stabilization upgrade for the gun, a gun elevation kill switch for the loader, improved ballistic drive and other component refinements. They were fitted with thermal sleeves on the barrels starting in 1973. During the mid 1970s it was becoming clear that the latest generation of composite based armor was impervious to tungsten carbide penetrators. Work was performed at the Department of Energy's Pacific Northwest National Laboratory to engineer development of depleted uranium as a penetrator material for future ammunition while the Armament Research and Development Command was improving the performance of the 105mm M774 cartridge. The M744A1 cartridge was issued starting in 1980 using a depleted uranium penetrator to keep the M68E1 gun viable against this improved armor. In 1975 an updated version of the gun, the T254E3 was designed, focusing on the use of chrome plating to improve accuracy. It was used to evaluate improvements to the gun's performance using discarding sabot ammunition. Two guns were built and underwent firing trials at Aberdeen and technical evaluations at the Watervliet Arsenal. Based on the results of these tests the shortcomings of plated bores and gun tubes were found to outweigh any advantage they might offer and the program dropped by May 1976.
In January 1978, a program was initiated to develop an enhanced version of the 105mm gun, the M68A1 as a possible alternate weapon for the M1 Abrams. The new XM24/L55 gun barrel was 18 inches longer in comparison to the XM24/L52 barrel used on the M60-series tank. It has a higher chamber pressure, reinforced breach and a higher muzzle velocity. Although the L11/M256 120mm gun was chosen to be the main weapon of the M1 Abrams in 1979, the ammunition for the gun was still not fully developed, thus delaying its fielding until 1984. The early production versions of the M1 Abrams were armed with the M68A1 for two reasons. First was due to the large number of M60 Patton tanks with the M68E1 gun still in widespread US service in the 1980s and a large on-hand stockpile of 105mm munitions. Fitting the M1 with the M68A1 gun was viewed as an economical and practical solution that allowed for commonality in ammunition among the two types of tanks. Secondly was the fact that the M68A1E2 could employ the newly developed M900 APFSDS depleted uranium round that had improved penetration performance in comparison to the M774. These early versions of the M1 Abrams were in active Army service until 1991 and with National Guard units until 1996. M1s built after 1984 were armed with the 120mm M256 and designated the M1A1. Many earlier M1 and IPM1 tanks were refitted with the M256 and their designations changed to the M1A1.
The M1128 Stryker Mobile Gun System carries the M68A1E4 105mm cannon. The principal function of the MGS is to provide rapid direct fire to support assaulting infantry. The cannon is mounted in a low-profile, fully stabilized turret integrated into the Stryker chassis. The M68A1E4 is based on the M68A1E2 105mm cannon's design. It has a sustained fire rate of six rounds per minute. The gun employs four types of cartridges. The M900 kinetic energy penetrator to destroy armored vehicles; the M456A2 high explosive anti-tank round to destroy thin-skinned vehicles and provide anti-personnel fragmentation; the M393A3 high explosive plastic round to destroy bunkers, machine gun and sniper positions, and breach openings in walls for infantry to access; and M1040 canister shot for use against dismounted infantry in the open. As of 2015, the M68A1E4 is the only variant of the M68 105mm gun still in active service with the United States.

Other users

The gun was subsequently adopted for use on the German Leopard 1. The L7A3 was also adopted by Japan for the Type 74 tank. The M68 gun is also featured on the Israeli Magach 6 and 7 series as well as early versions of the Merkava MBT. The Swedish Stridsvagn 103 turretless S-tank makes use of an indigenous gun design, which is compatible with ammunition 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.

Specification (L7A1)

AmmunitionOriginYearPenetrator materialMuzzle velocityProjectile masspenetrationNotes
L22United Kingdom1950sTungsten carbide
L28United Kingdom1959Tungsten carbide5.8 kg120 mm @ 60° at 914 mbuilt under licence by Germany as DM13
L36United Kingdom1960sTungsten carbide5.8 kg120 mm @ 60° at 914 mbuilt by UK for US as M392
L52United Kingdom1965Tungsten carbide tungsten alloy 120 mm @ 60° at 1828 mbuilt under licence by US as M728
Slpprj m/62Sweden1962Tungsten carbide 200 mm @ 30° at 1500 mSwedish-developed APDS round with a 57 mm sub-caliber projectile

AmmunitionOriginDesigner & producerYearPenetrator materialMuzzle velocityProjectile masspenetrationNotes
M735United States1978Tungsten alloy1501 m/s5.83 kg
M735A1United StatesPrimex Technologies1979Depleted uraniumnever fielded by the U.S. military
M774United StatesPrimex Technologies1980Depleted Uranium1508 m/s
M833United StatesPrimex Technologies1983Depleted uranium1493 m/s
M900United StatesPrimex Technologies1989Depleted uranium1505 m/s6.86 kg Cannot be fired by M68 only M68A1
FP105United StatesGeneral Defense Corporation1980sTungsten alloy1508 m/s5.8 kg Similar design to the M774, also known as C76A1 in Canada
M111 Hetz-6IsraelIMI1978Tungsten alloy1455 m/s4.2 kg NATO Single heavy target at 2000 mbuilt under licence by Germany as DM23
M413 Hetz-7IsraelIMI1980sTungsten alloy1455 m/s6.3 kg NATO Single heavy target at 6000 mbuilt under licence by Germany as DM43
M426IsraelIMITungsten alloybuilt under licence by Germany as DM63
CL3108IsraelIMIc. 1987Tungsten alloyexhibited relatively equal performance to the M833also known as FS Mk. 2 Improved or M429
M428 SWORDIsraelIMI2010sTungsten alloy1505 m/s
OFL 105 F1FranceGIAT1981Tungsten alloy1495 m/s3.8 kg 392 mm at point-blank range, 370 mm at 1000 m, NATO Single heavy target at 4400 m
OFL 105 G2FranceGIATc. 1987Tungsten alloy1495 m/s4.2 kg 477 mm at point-blank range, NATO Single heavy target at 6200 m
OFL 105 F2FranceGiat Industries1995Depleted uranium6.25 kg 520 mm at 2000 m
L64A4United KingdomRoyal Ordnance Factories1982Tungsten alloy1485 m/s3.8 kg NATO Single heavy target at 4000 m
H6/62United KingdomRoyal Ordnance Factorieslate 1980s/early 1990sTungsten alloy1490 m/s3.6 kg
NP105A2AustriaEnnstaler Metallwerkearly 1980sTungsten-nickel-iron alloy1485 m/s473 mm at 1000 m
M1060A3BelgiumMECAR2010sTungsten alloy1560 m/s6.2 kg defeat more than 500 mm at 2000 m
Type 93 APFSDSJapanDAIKIN1993Tungsten alloy

AmmunitionOriginYearType*Weight, complete round Projectile weight Explosive filling Muzzle velocity RHA penetration Notes
OCC 105 F1Francenon-rotating22.2 kg10.95 kg0.78 kg of HBX1000 m/s400 mm or 152 mm @ 64° at any range
M456 HEAT-TUnited States1966 fin-stabilized21.8 kg10.2 kg0.97 kg of Composition B1173 m/s375 mm or 175 mm @ 60° at any range
M152/6Israel2000sfin-stabilizedM152/3 upgraded with an airburst fuze
Type 91 HEAT-MPJapan1993fin-stabilizedDesigner & producer : KOMATSU

AmmunitionOriginYearWeight, complete roundProjectile massExplosive fillingMuzzle velocityNotes
L35A2 HESHUnited Kingdom1962
M393A1 HEP-TUnited States1960s21.2 kg11.3 kg2.99 kg of Composition A3732 m/s
M156 HESH-T Israel21.2 kg11.3 kg2.2 kg of Composition A3731 m/sIDF and is equivalent to the L35 HESH-T and M393A1/A2 HEP-T
Type75 HEP-TJapan1975

AmmunitionOriginYearWeight, complete roundProjectile massExplosive fillingMuzzle velocityNotes
OE Modèle 60France196021 kg12.1 kg2 kg of RDX/TNT770 m/s
Slsgr m/61 ASweden14.4 kg1.83 kg of TNT650 m/s
M110 HE-MP-TIsrael23.5 kg13.6 kg≈1 kg of CLX66800 m/Scapable of penetrating double reinforced concrete walls >200mm, its electronic fuze has three modes

AmmunitionOriginYearWeight, complete roundProjectile massMuzzle velocityFillingSize and durationNotes
L39A SMKUnited Kingdom1967
M416 WP-TUnited States1960s20.7 kg11.4 kg732 m/s
OFUM PH 105 F1France1960s18.5 kg12.1 kg695 m/s1,77 kg white phosphorus + 120 g hexolite burster charge75 m-wide smoke screen for 40 seconds

AmmunitionOriginYearTypeWeight, complete roundProjectile massMuzzle velocityFillingEffectsNotes
L15A1 CANUnited Kingdomcanister
XM494E3 APERS-TUnited Statesbeehive25 kg14 kg823 m/s5000 steel flechettes
105mm APAM-MP-T M117/1 CartridgeIsrael2000s6 submunitions
M436 STUNIsrael2000sless-than-lethal14.4 kg2.5 kgplastic flakesproduce flash, bang and blast effects"less-than-lethal" cartridge

AmmunitionOriginYearWeight, complete roundMissile massSpeedRangeWarheadRHA penetrationGuidanceNotes
FALARICK 105Ukraine & Belgium2010s24subsonic5000 mtandem HEATnot less than 550 mmsemi-automatic by laser beam
LAHATIsrael1990ssubsonictandem HEAT

Variants

UK models


L7 variant