In 1965 a General Staff Requirement was approved for a new 105 mm weapon system because the pack howitzer 'lacked range and lethality'. Key characteristics included use of 105 mm Fd Mk 2 ammunition designed for the L13 ordnance of the Gun Equipment 105 mm L109 (better known as Abbot self-propelled gun), 6400 mil traverse by one man, maximum weight 3500 lbs, dimension limits imposed by internal carriage in Chinook helicopters and Andover transport aircraft, and the ability to fire immediately after being under water for 30 minutes.
The new gun, soon designated 'Light Gun', was designed by the government Royal Armament Research and Development Establishment (RARDE), Fort Halstead, Kent. Prototypes were tested in 1968. However, it soon emerged that some increase in weight was needed for a gun with the requisite robustness and several assemblies were substantially redesigned.
The Abbot ammunition uses electrical instead of percussion primers and provides greater lethality and range than the US M1-type ammunition. It is an entirely different design to the US M1 type ammunition and the two are not interchangeable, although 105 mm Fd Mk 1 uses the M1 shell, which is shorter with less HE than the 105 mm Fd Mk 2 design. The original Light Gun requirement was to use 105 mm Fd Mk 1 ammunition in training. However, in 1968 this was changed to allow a second ordnance capable of firing US 1935 pattern (ie M1) ammunition.
The L118 uses the L19 ordnance on the L17 carriage. The L19 ordnance is slightly shorter than the L13 used by Abbot and hence has slightly less maximum range.
Original production, which was authorised in late 1975, was by Royal Ordnance Factory, Nottingham (Government owned) which has since been incorporated into BAE Systems Land and Armaments. Deliveries started in 1976.
However, a new vehicle, the Land Rover 101 Forward Control (Land Rover, One Ton) was designed as the prime mover in the field for the Light Gun (and the Rapier air-defence missile launcher). Since the end of the 1990s, the British Army has been using Pinzgauer ATVs as their gun tractors. In Arctic service, and elsewhere, the gun is towed by the Hägglunds Bv 206 and is fitted with skis when over snow.
In 1982, the Light Gun saw intense use in the Falklands War. Five batteries (30 guns) were deployed to the Falkland Islands. During the final phases of the battles around Port Stanley, these guns were firing up to 400 rounds per gun per day, mostly at "Charge Super" i.e. the most powerful propellant charge for which they were designed. They were a significant factor in the British victory. Since then, British forces have used the Light Gun in combat in the Balkans, Sierra Leone, Iraq and Afghanistan.
At present, the British Army deploys the Light Gun with 29 Commando Regiment RA, 7th Parachute Regiment Royal Horse Artillery and 40 Field Regiment RA. These units support Marine Commando, Air Assault or Light formations. Other regular batteries are temporarily converted to the Light Gun from the AS-90 self-propelled gun as necessary for operations.
Three regiments of the Territorial Army (100 Regt. RA(V), 103 (Lancastrian Artillery Volunteers) Regt. RA(V) and 105 Regt. RA(V)) are also equipped with the Light Gun. The Honourable Artillery Company, 104 Regt. RA(V) and other units use the Light Gun for ceremonial purposes.
Those University Officer Training Corps with "Gun Troops" train with the L118.
The narrow wheelbase prevents the ordnance rotating the 3200 mil required to 'unfold' the gun. Because of this, the gun features a knock-off hub on one side allowing the ordnance to be rotated by removing one wheel. With a well trained gun crew, this contributes approximately 30 seconds to the time required to deploy the gun.
When being towed in the unfolded position, the A-Frame is fitted to the front transom in order to support the elevating mass. A recent modification makes it possible to keep the gun in this position indefinitely at speeds up to 40 mph. For long distance transport or traversing rough terrain, the barrel is reversed and clamped to the end of the trail. For storage, the gun is in the unfolded position with the barrel elevated to an angle that balances the elevated mass on the yoke and therefore relieves pressure on the elevating gears.
When first introduced in the British Royal Artillery, the L7 or L7A1 dial sight and its carrier, incorporating an integral elevation scale and internal lighting powered by Trilux nuclear light sources, was used to aim the gun for indirect fire. Since Light Gun entered service after the introduction of Field Artillery Computer Equipment (FACE) it never, unlike Abbot, had gun rules. Therefore it has a single Quadrant Elevation scale. These optical indirect fire sights are now only used in recruit training. The L7 sight is a modified version of a German Leitz instrument.
The guns also have a direct fire telescope and were originally issued with a night telescope using image intensification.
Both Charge 5 and Charge Super project beyond the end of the metal cartridge case. Unlike the M1 ammunition, which is 'semi fixed' and loaded as a complete round, 105 mm Fd is 'separate'; the shell is loaded and rammed by hand then the cartridge is loaded. By the time L118 entered service sub-zones A and B originally used with Abbot had been replaced by a spoiler to reduce the minimum range at high angle fire when this was required.
The 105 mm Fd Mk 2 projectiles are the same as used with Abbot, apart from the current introduction of a new L50 HE shell and L51 red phosphorus smoke shell. The new HE is slightly longer than current shells, uses insensitive plastic bonded explosive and provides significantly greater lethality, which the supplier claims is equivalent to 155 mm HE M107. A base-bleed HE shell, maximum range reportedly 21 - 22 km, was developed in the late 1990s but has not entered service.
In 2002 the British Army's L118 guns completed replacement of their optical sights with the Artillery Pointing System (APS) LINAPS This is a self-contained system that uses ring laser gyros to determine azimuth, elevation angle and trunnion tilt angle. It also includes facilities for navigation and self-survey using Global Positioning System, inertial direction measurement and distance measurement. All this can be used anywhere in the world to lay the gun without external references. An upgraded APS may also perform some ballistic calculation functions including muzzle velocity prediction using Kalman filters or a neural network.
A capability enhancement program that started delivering improvements to UK guns in 2007 aims at reducing weight and improving some components. Weight reduction measures include replacing some steel components with titanium. The MVMD is also more tightly coupled with the layer's display unit of the APS, reducing electrical power requirements.
The Indian 105 mm light gun appears to share many features with the UK equipment. In the late 1960s India introduced the Value Engineered Abbot variant with the 105 mm Fd ammunition.
Production facilities were established in Australia (for Australian and New Zealand), where it is called the 'Hamel Gun', and the US as M119A1.