Rheinmetall has developed a new 120 mm smoothbore gun with a calibre length of 55 (L55) which is a direct replacement for the current 120 mm smoothbore gun with a calibre length of 44 (L44) which is standard on all production Leopard 2 series MBTs.

This 120 mm L55 barrel is 1.30 m longer than the current barrel and this leads to a significant increase in muzzle velocity, especially with the latest APFSDS-T rounds which have more propellant and new penetrators.

The geometry of the chamber and the pressure limits are defined in the quadrilateral Interface Control Document (ICD) for the 120 mm tank main armament systems.

In accordance with the ICD, the Rheinmetall 120 mm L55 has the identical chamber geometry as the current fielded L44 barrel and complies with the pressure limits. This means that all current 120 mm projectiles can be fired from the new 120 mm L55 barrel.

In order to minimise the extent of the changes, the interface measurements of the 120 mm L55 to the breech and of the current 120 mm L44 to the cradle are unchanged. The weapon is fitted with a thermal sleeve, fume extractor and muzzle reference system.

According to Rheinmetall, two further improvements are possible with the latest 120 mm L55 barrel. First the breech could be made from the same steel as the barrel and this would increase the pressure load of the gun by 500 bar compared with the current L44 weapon.

Second, the design of the 120 mm L55 barrel permits a higher pressure load over a longer range of the barrel than is known from the fielded L44 barrel. So the new L55 barrel is prepared for future interior ballistics which are expected to show a wider maximum pressure instead of the now usual pressure peak.

During the extensive trials programme with prototype 120 mm L55 weapons, the hit accuracy was tested with existing ammunition as well as with the latest kinetic energy types such as the DM43A1 and the DM53. The results show the same dispersion characteristics as the current 120 mm L44. Trials have shown that the lengthening of the barrel results in an increase of muzzle energy of about 14 per cent when compared with the latest field APFSDS round.

It is expected that Germany and Netherlands will be the first countries to refit at least part of their current Leopard 2 fleet with the new L55 barrel.

Development, technical testing and field trials of the 120 mm L55 gun were completed in 1998. Starting in the year 2000, the current Leopard 2A5 MBT's of Germany and the Netherlands will be retrofitted with this new gun. The Leopard 2A5 will then be designated the Leopard 2A6.