Royal Ordnance L11
The Royal Ordnance L11 is a 120 mm L/55 rifled gun developed by the British in 1957. The basis of the design came about with Britain believing their tanks should engage enemies outside of their firing range, thus they need a higher caliber cannon able to produce the muzzle velocity to send the round far. It features innovations such as the usage of the large 120 mm caliber and also bagged charge rounds that helped in the loading process.
- L31 High Explosive Squash Head (HESH)
- L15 Armour Piercing Discarding Sabot-Tracer (APDS-T) (production discontinued)
- L20 Discarding Sabot-Training (DS-T)
- L23 Armour Piercing Fin Stabilized Discarding Sabot (APFSDS)
- L34 Smoke
- L32 Squash Head-Practice (SH-P)
- L35A1 canister shot
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In 1957, the engineers of the Royal Armament Research and Development Establishment at Fort Halstead developed a new type of rifled cannon chambered for a 120 mm shell. The large caliber was made under the specifications by the British Army for tanks to be able to engage armor beyond the enemy's effective range at about 2,000 meters. The gun was made to be mounted on the new main battle tank in development at the time, the Chieftain tank. The gun was designated Royal Ordnance L11 with many variants produced as upgrades.
The gun is unique in comparison to other tank armament by its ammunition. Rather than a fixed ammunition, the gun used a two-piece ammunition with a separated primer. The projectile was loaded first, with the propellent next; the gun mounts a 10-round Vent Tube magazine that acts as the primer for the gun. The propellant loaded in is a form of bagged charge, a feature on naval ships that has transitioned over to tank technology. Bagged charge benefited over regular brass cases with an easier loading process due to lighter weight, smaller size for increased stowage, and the removal of toxic gases since the whole propellant was used when fired. The downside of the bagged charge's use of a two-piece ammunition, the reload time, was deemed negligible as testing showed the two-piece ammunition did not significantly hamper the average reload time and firing rate. Another concern in the design process was crew safety and protection against catastrophic ammunition fires. The bagged charge helped this process by being placed along with HESH shells in the bottom hull surrounded by a water jacket similar to the M4 Sherman's wet stowage system while the APDS rounds, which were inert, stayed in the turret for ease of access.
The gun was operated with a semi-automatic breech block and was initially ranged by a .50 caliber machine gun out to 2,600 meters. This was removed in the 1970s when laser rangefinders became more prevalent and replaced the machine gun. The gun was first produced as the L11A1 before upgrading to the A2 with reinforced structure, the A3 with changes to the breech ring, and the A5 was the main production model with lighter fume extractor, with the A6 being converted A3 into the A5. The A4 variant existed as a evaluation model for an auto-loading system.
The L11 gun saw mainly saw service on the Chieftain Main Battle Tank. It was a formidable gun on the Chieftain and gave it firepower nearly unrivaled until the advent of the German Rheinmetall 120 mm gun. The L11 also saw use on the new British main battle tank Challenger 1 in the 1980s, which it served well with the British in the Gulf War. In the British involvement in the Gulf War, codenamed Operation Granby, a Challenger 1 set a record with its L11A5 gun by scoring the longest tank-to-tank kill in history by destroying an Iraqi T-72 at a distance of 5,100 meters, or 3.1 miles.