Royal Ordnance Nottingham successfully completed design work to enable the 105 mm L7A3 gun to be installed in the Russian-built T-54/T-55 MBT.

This conversion significantly improves first round hit probability and enables the latest high-performance kinetic ammunition to be fired. The original 100 mm D-10TS gun (in the T-55) is loaded from the right but in Western tanks loading is from the left. The L7 has, therefore, been turned through 180°. A revised recoil system has been designed which includes new buffer components and modified recuperator, so maintaining trunnion pulls consistent with the original system and a rebalanced elevating mass.

Other work has included the design and manufacture of two fuel tanks positioned in the hull with new ammunition racks integral with the fuel tanks, modified main and emergency firing circuits and a new telescopic graticule to suit the new range of 105 mm ammunition and the coaxial 7.62 mm machine gun.

An additional advantage of this conversion, which has been carried out at the original request of Egypt, is that the gun barrel can now be withdrawn through the cradle; in the past the complete T-54/T-55 tank turret had to be removed.

A similar conversion but involving the fitting of an improved elevating mass, comprising a new cradle and recoil system, has also been carried out on a Chinese-built Type 59 MBT of the Pakistani Army.

As far as it is known, the only customer for this upgrade package is Egypt.

Development complete. Production as required. Ordered by Egypt for its T-54/T-55 MBTs in June 1985. The Chinese Type 59 conversion has been evaluated in Pakistan but has yet to enter series production.