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INTRODUCTION

The Light Gun was designed and continues to evolve to meet British needs.  They have used it on operations on four continents and trained with it from the Arctic to the Equator.  About 1200 Light Guns have been provided to the soldiers and marines of about 20 countries including licensed production in Australia and the US.  There are two versions, L118 ‘the real thing’ and L119 (M119 in US service).  Although called a Gun by UK, both versions have characteristics of a howitzer, variable propelling charges and high angle fire capability, but with comparatively high muzzle velocity and long barrel length.

ORIGINS

There are several threads to Light Gun’s UK origins.  One probably starts with Sgt Farrell and Bdr Cliff Jones, RA artificers in 129 Jungle Fd Regt inventing the Jury Axle 25-pr in late 1943.  Another was the need to replace the 75 mm in airborne artillery, the highest priority in 1947 and a joint program with Canada.  The Suez Campaign in 1956 was another factor, being the last UK airborne assault and the first (globally) amphibious assault by helicopter.  In its aftermath the 1957 Defence Review created Army Strategic Command and by ending national service (the last left in 1962) it spelt the end of the mass TA and led directly to the L119 version of Light Gun. 

Strategic Command was the first ‘Rapid Deployment Force’.  Its main elements, based mostly in UK, were a parachute brigade and three airportable brigades.  All required light artillery and 75 mm was clearly not the solution; Suez highlighted that ‘third world’ armies could be equipped with modern Soviet equipment.  The need for new light artillery went beyond Strategic Command with regiments assigned to the RM commando brigades in UK and Singapore and the two standard field regiments in Malaya and Hong Kong.

In the 1950s NATO agreed that 105 mm was to be a standard calibre but did not define its ballistic and other characteristics, it is a widely held mis-conception that there is 'NATO standard 105mm', there is no such thing.  This stopped UK work on the new 88 mm field gun as well as UK and US design studies for 110 mm.  UK recognised the deficiencies of the widely used US ‘1935 pattern’ 105 mm ammunition and switched efforts to a new 105 mm round, which may have been a scaled up version of the new 88 mm round. 

However, the need for a new gun was pressing, light weight was essential and the only option was Oto-Melara’s 105/14 Model 56 mountain howitzer.  It was adopted as 105 mm Pack Howitzer L5 (L10 Ordnance) in 1959 and towed by ¾ ton Landrover.  It entered service in 1961 and was first used in action in 1962 mopping up after the Brunei Revolt.  Meanwhile development of the self-propelled replacement for the 25-pr had started.  This 105 mm Gun Self Propelled L109 (L13 Ordnance and called Abbot) started trials in 1962.  It used an entirely new ammunition ‘family’ officially designated ‘105 mm Field’ (105mm Fd), but often called ‘Abbot ammunition’; Mk 2 being the real thing while Mk 1 used a new reduced cartridge and the old 1935 pattern shell.  Both cartridges used an electrical, not percussion, primer.  In UK service ‘1935 pattern’ (ie US 105 mm M1 round) was called ‘105 mm How’ (and avoided confusion with '105 mm Tank'). 

UK HISTORY

Consideration of the Pack How L5 replacement started almost immediately after it entered service in 1963.  The final version of General Staff Requirement (GSR) 3058 for a “Light Weight Close Support Weapon System” was formally approved in April 1965.  The title was soon changed to “105 mm Light Gun”.  Design and development by the Guns Division of the Royal Armament Research and Development Establishment at Fort Halstead in Kent then started leading to trials in 1968.  Five amendments were made to the GSR during 1965-68.  The project was notable in being the first with a designated military Project Manager, albeit without the necessary authority, procedures and recognition by key participants such as the design authority and manufacturer’s managers who were civil servants and ‘outranked’ him!

Development and trials of the L118 Light Gun (L19 ordnance using 105 mm Field Mk 2 ammunition) were completed by 1969.  The accepted design, in 1970, had a fighting weight of 1860 kgs.  An interregnum of some 5 years then ensued.  The reasons for this are unclear but probably reflected changes in UK Defence Policy, budgetary pressures and lack of a towing vehicle.  In the event approval for manufacture was given on 8 Sep 1975 and the gun entered UK service the following year with the order completed in 1977. 

The GSR had estimated 250 guns for UK service, on the high side for about 20 batteries of various sizes.  However, actual acquisition was about 14 batteries, but there may have been a further order in 1982-3 after the campaign in the Falkland Islands.  In 2005 UK stocks were 126 L118 guns with 130 spare barrels and 16 L118 saluting guns. 

DESIGN AND DEVELOPMENT

The GSR stated the requirement was for operations outside Europe.  It also stated “The present light weapon, the Italian 105mm Pack Howitzer L5, though the best currently available, lacks range and robustness.  Its shell is of old design and its lethality compares unfavourably with more modern designs”.  Importantly the GSR stated it covered “the development of a 105mm weapon system as ammunition, weapon and vehicle characteristics are interacting”.  The Pack Howitzer used the US M1 round, a 1935 design.

However, the GSR also specified that it “must fire the Abbot Mk 2 projectile and as many components as possible of the Abbot Mk 2 cartridge” and required a maximum range of at least 15km.  This suggests some doubt about what was possible because Abbot achieved 17.3 km with charge Super and 15 km charge 5.  There was also a ‘desirable’ - a rocket assisted or sub-calibre projectile giving 20 km, with criteria for acceptable reduced lethality and consistency.  It seems that an acceptable shell was not developed at that time.

The required indirect fire minimum range was 2.5 km with a Quadrant Elevation (QE) not less than 200 mils (low angle fire) and at high angle.  At this time Abbot used the special L1 cartridge for this.  This was replaced by spoilers fitted to shells for high angle fire by the time Light Gun completed development. 

Required firepower characteristics were: desirable burst rate of fire 3 rounds in 10 seconds, 6 rounds per minute for 2 minutes and desirably for 5 minutes, sustained rate 2 rounds per minute and desirably 3, for 30 minutes.  Barrel life of 10,000 Equivalent Full Charges (EFC).  Other parts of the GSR included:

• Elevation from -100 to 1250 mils.
• Direct fire up to 3000 metres, anti tank (firing HESH) to 1500 metres with 65% probability of a first round hit and 90% for the second, with investigation of achieving all this at night (an image intensification night sight was adopted).
• Top traverse at least 75 mils left and right, and one-man laying.
• A platform that did not require use of pickets and the ability for one man to swing the gun through 6400 mils rapidly and easily.  This meant a box trail, platform and a well balanced gun.  
• Into and out of action in less than two minutes.

The key physical constraints were weight and dimensions, the former was explicit: fighting weight was not to exceed 3500 lbs (about 1590 kg and almost identical to 18-pr on Mk 5 carriage).  The barrel was autofrettaged (unlike the L13 ordnance used by Abbot) to minimise weight.  Fighting weight includes essential gun stores, although these may be carried in the gun tractor.  The fighting weight was probably based on under-slung carriage by Wessex HC2/HU5 helicopters.  Dimensions were set indirectly by the need to minimise weight and carry gun and towing vehicle inside Andover and Chinook aircraft.  This combination gave an overall dimension envelope about 8.5 m long, 2.1 m wide and 1.9 m high.  Of course width also had to permit men to move along the side in the aircraft (not least to fit and remove tie-downs) and height had to allow for the muzzle going up as the gun was backed-up and towed down the aircraft’s tail ramp. 

These air transport requirements left about 5 m for gun length; height was also a problem – the gun is 2.6 m high with the barrel secured forward.  This meant either a retractable barrel or reversing the barrel to a travelling position with the muzzle over the spade.  The latter was chosen giving 4.9 m folded length, the initial gun tractor was about 3.5 m long. 

In September 1965 two environmental requirements were added to the standard ones: the minimum firing temperature was lowered to -25°F (-32°C),desirably -40°F (-40°C), and firing immediately after 30 minutes submersion in fresh or salt water.  The latter made particular reference to the electrical firing mechanism and the sights.  The temperature was recognition of the new role of the Royal Marines and of the Royal Artillery component of the Allied Command Europe (ACE) Mobile Force on the European northern flank.

Unstated was the 1947 policy decision to abandon calibrating sights for gun rules and sight mounts with separate internal Tangent Elevation (TE) and Angle of Sight (AoS) scales.  The method of illuminating sights was not mentioned.  Similarly unstated was a dial sight for bearing laying, UK having changed from deflection laying in the 1950s.   However, the GSR did seek compatibility with improved fire control systems and an amendment in 1967 added the need for FACE computer programs.

Comparison of the 1968 prototypes and the production guns reveal significant differences in the carriages, the original carriage was designated L12, the production L17. Changes included:

• The original electrical firing mechanism was completely redesigned.
• Fighting weight increased by just over 300 kg, most (200 kg) in the elevating mass including redesigned recoil system and 46 kg more in the ordnance.  Folded length increased by 15 cm, a completely new platform added 62 kg despite replacing 25-pr style rigid stays with cables, and overall width increased by about 25mm.
• The dial sight, a modified German Leitz instrument, had its micrometer scales on the right, this was changed to the left. 
• The introduction of FACE meant only Quadrant Elevation (QE) main and micrometer scales were needed in the sight mount, because the computer produced a QE for each gun, so a complete redesign of the sight mount removed the TE and AoS scales.

The GSR also stated some ‘wish list’ items that proved impossible due to weight and size constraints.  These were auxiliary motive power to self-propel the gun at slow speed over 5 – 10 miles, power takeoff from the tractor to drive the gun wheels and for the gun to be broken down in major components that could be man-handled by the detachment.  A collection of requirements that suggests the GSR authors believed in miracles given the weight and size constraints.

In UK service the gun could not be divorced from its towing vehicle, not least because the GSR said they had to be treated as a system and referred to a new ¾ ton 4×4 and a future GS 1½ ton 4×4.  The extra weight of the gun probably closed the ¾ ton Landrover option and the future 1½ ton 4×4 turned into the GS 1 tonne 4×4 Landrover (gross weight about 3 tonnes) that entered service in 1975 and was used as the gun tower.  The GSR stated that a sub-section should carry about 60 rounds, which weighed at least 1.6 tonnes so each gun needed two vehicles (towing and ammunition), which was already the case with the Pack Howitzer.  However, two batteries used another vehicle, the tracked and articulated BV202 towed the gun fitted with skis over snow. 

The similar BV206 replaced BV202 in the 1990s and the 1 tonne was replaced by the Reynolds Boughton RB44 (gross weight 5 tonnes) based on Ford components.  The Pinzgauer 6×6 (maximum gross weight 4800 kg, with about 2 tonne cargo, maximum ‘trailer’ weight off-road 1800 kg (5000 kg on road)) replaced it in field force units in the 1990s.  The Road Traffic Act, which MoD tries to comply with, requires compliance with the vehicle manufacturer’s recommended maximum train weight so gun weight over 1800 kg is an issue.

L119 and M119

The final issue was alternative ammunition, primarily for training.  The GSR originally stated “It is desirable that the weapon should be able to fire existing 105 mm M1 projectile, albeit to a lesser range.”  This meant Abbot Mk 1 ammunition (separate loading) which used the M1 type shell and reduced Abbot cartridges (L32 charges 1 – 4 and L34 Super) to give a charge Super maximum range of 15 km.  This was transitional ammunition for Abbot to allow production of stocks of Abbot Mk 2 ammunition.  However, in June 1968 the light gun requirement changed to “It is desirable that the weapon should be able to fire the complete 105 mm M1 ammunition system.  For this a separate ordnance is acceptable.”  This change reflected the disbandment of the mass TA because originally 105 mm Pack How replaced in the regular army by the new Light Gun were earmarked to replace the TA 25-pr.  No mass TA freed the stocks of M1 type ammunition.  The result was Light Gun L119 with its L20 ordnance and a percussion firing mechanism, of course there’s no reason why L118 could not fire‘Abbot Mk 1’.

Two batteries of L119 were acquired to support the Royal School of Artillery, they entered service at the same time as L118.  L119 were removed from UK service in 2001 (when stocks of M1 type ammunition ran out), declared obsolete in 2002 and the remaining 7 guns with 5 spare barrels were disposed of.   

Most export customers have acquired L119 rather than L118, the attraction being the inferior performing but more but more widely available and probably cheaper M1 ammunition.  Arguing military effectiveness with national treasuries is not the easiest task!

The M119 Howitzer is a US built L119 with minor modifications, notably replacement of the Leitz design dial sight with a standard US panoramic telescope for deflection laying.  There are some other minor 'amecanizations' replacing some components with US standard equivalents and lowering the operating temperature envelope down  to -45°C.  It entered service in 1989.  Most recently M119s have received US digital sights (M119A3).

Hamel guns are carriages with both L19 and L20 ordnances built in Australia for Australia and New Zealand, albeit with some UK built components in the early guns.  They entered service in the early 1990s and it appears that they were several times (some sources report x20) the cost of UK built guns.  Plans to produce 105mm Field ammunition for L118 did not eventuate.  Hamels left Australian service in 2013 with their L19 ordnances hardly used.   New Zealand guns have been upgraded with digital sights, as have those of many other users.  

In the 1960s India purchased value engineered Abbot SP guns for their armoured divisions.  This seems to have included licensed production of 105mm Field ammunition leading to the Indian produced 105mm Indian Field Gun and later Light Field Gun.  These have many features in common with L118, whether these are a result of design transfer or 'imitation is the sincerest form of flattery' is unclear.

AMMUNITION

In World War 2 most UK artillery ammunition, including 25-pr, was behind the designs of other countries.  Learning from World War 1, UK had selected ease and cost of large scale mass production ahead of munition fragmentation, given UK’s neutralisation doctrine this was reasonable sense.  The World War 2 period ammunition designs set the norm for HE shell at around 15% HE by weight.  UK designs, except for the 5.5 inch 80 lb shell introduced mid-war, were less than 10%.  Wartime research indicated the optimum HE shell design was around 25% HE, this was not achieved anywhere until the 1970s.

The UK 105 mm ammunition uses N and NQ triple base propellant that was increasingly used by UK (eg 25-pr) in World War 2.  It’s HE shell is about 7% heavier, 10% longer with 20% more HE than the US 1935 pattern.  The cartridge has an electrical primer, and the shell and cartridge are loaded separately, the shell being power rammed in Abbot but hand rammed in Light Gun as it was with 25-pr.  Apart from the electric primer it seems likely that the ammunition design was derived from the round under development in the early 1950s for the 88 mm gun that was backwards compatible with 25-pr.

L118 used the same shells and cartridges as Abbot.  There are two cartridges: L35 with charges 1 – 5 and L36 charge Super.  Charge bags are colour coded in accordance with normal UK practice: Charge 1 red bag, then white, blue, orange and the green Charge 5 increment, these total 3.25 kg of propellant.  Both Charge 5 and Super (brown) project beyond the cartridge case, below Charge 5 the cartridge case is topped with a polystyrene cap.  UK had produced a new series of fuzes for the ammunition when it entered service in the 1960s.

However, gun limitations mean there are maximum elevation limits for charges 5 and Super in high angle fire.  This increases the minimum high angle range for these charges.  Therefore Charge 4½ is used to ensure adequate range overlap above Charge 4, this comprises Charge 5 with the blue Charge 3 bag removed.  A spoiler ring can be fitted over the shell ogive to reduce the minimum high angle range with Charge 1.

The original projectiles were: HE, Base Ejection (BE) Smoke, Orange and Red Marker, Illuminating, HESH and Prac (inert HESH).  Fuzes include Point Detonating (PD), PD and Mechanical Time (MT), Controlled Variable Time, and MT for BE Smoke and Illuminating.  A hand fuze setter, No 4, was used with the various Time fuzes (except the vernier scale Dixi fuze used with illuminating).  A Multi-Role Fuze, L116, was introduced in the 1990s to replace CVT and PD fuzes and an Electronic Time Fuze, L132, for BE Smoke, both were set using a new Fuze Setter, Electronic.  The Bofors illuminating shell retained its Dixi MT fuze due to the need for compatibility with the cargo ejection arrangements.

Ammunition is packed in steel, not wooden, boxes, a long standing British practice.  One box holds two shells each in a paperboard tube, a slightly larger box holds two cartridges, each in a plastic container.  A pallet holds 36 boxes (36 complete rounds).

Ammunition costs, shortly after Light Gun entered service were:

      HE shell - £31
Smoke shell - £144
Illuminating shell and fuze – £230
Normal cartridge - £57, Super - £52  (including brass cases £28 which were recoverable salvage
Fuzes –
the original direct action fuze £32, replaced by cheaper fuzes £20 
Time fuze for smoke £49
VT fuze £74

LATER DEVELOPMENTS

Light Gun continues to evolve.  The first significant change was in the 1990s when every gun was fitted with a Muzzle Velocity Radar (MVR) as part of a wider program.  Next came the replacement, completed n 2002, of optical sights and directors (aiming circles) by the self-contained Automatic Pointing System (APS).  APS includes an Inertial Navigation Unit (INU) mounted above the barrel with three ring-laser gyroscopes to provide continuous bearing, elevation and trunnion tilt angles, and automatically compensates the former for the last.  The Layer’s Control and Display Unit (LCDU) replaces the sight mount.  The only guns not fitted with APS are those used for recruit training.  

The No 1 (gun detachment commander) in the towing vehicle has a remote Navigation Display Unit (NDU).  The NDU uses the INU’s continuous ‘self-survey’ from the Global Positioning System with backup inertial and distance measurement (gun wheel hub odometer).  The NDU can also be used as a backup LCDU.  The electronics mean the power supply is an ‘essential store’.  All this increased weight, despite savings from the sight mount and some previously essential stores such as aiming posts and parallelescope. 

In the late 1990s UK announced that 155mm would replace Light Guns by 2010 and joined the US in funding BAE’s 155 mm M777.  This decision was rescinded some years later because there was no realistic prospect of sustaining 155mm over the air assault distances envisaged by UK doctrine.  The need to extend life and reduce weight led to a Capability Enhancement Program that started deployment in 2007.  Its main features include:

• A new electrical power system, providing 24 hrs power without charging and a silent generator (to power MVR and APS).
• Integration of MVR with APS including the LCDU displaying and storing fired MV data. 
• NDU Improvements giving a colour map display and digitally stored equipment manuals.
• New lightweight rock spade using titanium and aluminium platform instead of steel, cost stopped acquisition of these.
• Replacement of the ‘A’ frame, used to secure the elevating mass when the gun is towed in the forward position, with a single strut and traverse lock.  
• New braking system including improved handbrake.
• Handgrips added to the trails to make it easier to lift the trail for hooking to the towing vehicle.
• Extended towing eye to enable a tighter turning circle when being towed.
• New maintenance free recoil system with fewer parts and improved seals. 
• A new direct fire sight based on a sniping telescope, almost doubling the HE range of the old one, assisted by No 1’s laser range finder and supported with ballistic calculations by the LCDU, the sight appears to be limited to use in Afghanistan.
• After a decade of service a new LCDU has been introduced, it features a touch-sensitive electro-luminescent display, includes the NATO Armaments Ballistic Kernel (NABK) for ballistic calculations (probably limited to direct fire) and support for additional data interfaces.

Replacement of the A frame means that it is no longer essential to rotate the barrel for towing, although the traverse gear still has to be disconnected.  A hinged stub axle so that the barrel could be rotated just by jacking the wheel without removing it has not been adopted by UK.  

Ammunition development has not been neglected.  A new general purpose HE shell, L53, is being adopted, it is 5% longer than the current one, has the same weight and ballistic characteristics and complies with the insensitive munitions regulations, explosive content being over 19%.  Lethality is enhanced by around 20%, and the manufacturer claims it has the same lethality as 155 mm HE M107, although probably only against certain target types.  A new base ejection red phosphorus smoke shell, L52, provides multi-spectral screening.  An insensitive extended range shell has also been developed, this uses base bleed to give 20.6 km maximum range although close to 22 km has been achieved in ‘hot and high’ conditions.  Nevertheless, it’s unlikely to enter service until a course correcting fuze is available.  Updated white light and new blacklight iilluminating have been introduced.   However, HESH is no longer in service and coloured marker stocks are not being replaced.  

New fuzes are being adopted, a Multi-Function Fuze for HE (L166) and a new Electronic Time for smoke and illuminating (L163).  These fuzes are set using a new induction fuze setter (L7). 

Light Gun is expected to remain in UK service until 2030.

Copyright ©  2011 - 2015   Nigel F Evans. All Rights Reserved.