The 105 mm Improved Weapon System (IWS) was announced late in 1989 and has been developed for the export market as a private venture by Royal Ordnance. The high-pressure IWS has a rifled barrel of Electro-Slag Refined (ESR) steel fitted with a fume extractor, thermal sleeve, horizontal sliding breech mechanism and pepperpot muzzle brake that reduces recoil forces by 25 per cent. The interior of the IWS ordnance is chrome lined to give increased barrel life.

Royal Ordnance can offer an automatic muzzle reference system for the Improved Weapon System mounted on a forged upstand on the barrel. This will improve the accuracy of the system and greatly enhance the single-shot kill capability.

Firing a new Royal Ordnance developed 105 mm APFSDS round, Royal Ordnance claims performance penetration equivalent to a 120 mm smoothbore gun, superior to all current 105 mm APFSDS rounds. No actual details of penetration have been released but, based on available information, penetration of 540 mm of rolled homogeneous armour at a range of 2,000 m is probable.

The new IWS is almost a direct replacement for the current 105 mm L7 and uses the existing recoil system and cradle. The existing sight graticule would have to be modified as well as thefready racks)to accommodate the new 105 mm APFSDS rounds. The IWS was demonstrated late in 1989 fitted in a Leopard 1 MBT. Conversion work can be carried out at base workshop level with no special equipment being required.

A new high-performance APFSDS round with conventional material penetrator of tungsten nickel iron, rather than depleted uranium (DU) and a semi-combustible cartridge case, has been developed by Royal Ordnance.

The new APFSDS round weighs a total of 19 kg and is 1.03 m long with a muzzle velocity of 1,420 m/s. The Tungsten-Nickel-lron (W-Ni-Fe) long rod penetrator, manufactured by Royal Ordnance Speciality Metals, is located in a three segment sabot which has been designed to reduce parasitic weight to a minimum.

The length-to-diameter ratio is 23:1. The new round does not have a tracer element and the fins of the projectile are of steel.

According to Royal Ordnance, the penetrator has a mass approximately 40 per cent greater than that of current 105 mm APFSDS rounds.

The propelling charge comprises a stub brass cartridge case and a combustible sleeve which together house the multibase granular propellant and primer.

The IWS can fire all existing 105 mm NATO rounds including APFSDS and training types. Built-in safety features ensure that the new high-pressure round cannot be loaded into standard 105 mm L7 guns or into an IWS incorporating L7 components.

So far, the IWS has been installed in an early Leopard 1 MBT (form and fit trials), a C1 Leopard 1 MBT of the Canadian Forces (firing trials in the UK) and, late in 1991, in a German Army Leopard 1A5 (firing trials).

Late in 1993 the IWS was successfully demonstrated in Italy installed in a Leopard 1 of the Italian Army and early in 1994 was demonstrated in Canada installed in a C1 Leopard MBT.

As of mid-1999, no firm orders have been placed for the 105 mm Improved Weapon System.