It was designed by Vickers Defence Systems (now Rheinmetall BAE Systems Land (RBSL)) as a private venture in 1986, and was an extensive redesign of the company's earlier Challenger 1 tank.[11] The Ministry of Defence ordered a prototype in December 1988. The Challenger 2 has four crew members consisting of a commander, gunner, loader, and driver. The main armament is a L30A1 120-millimetre (4.7 in) rifled tank gun, an improved derivative of the L11 gun used on the Chieftain and Challenger 1.[12] Fifty rounds of ammunition are carried for the main armament, alongside 4,200 rounds of 7.62 mm ammunition for the tank's secondary weapons: a L94A1 EX-34 chain gun mounted coaxially, and a L37A2 (GPMG) machine gun. The turret and hull are protected with second generation Chobham armour, also known as Dorchester. Powered by a Perkins CV12-6A V12 diesel engine, the tank has a range of 550 kilometres (340 mi) and maximum road speed of 59 kilometres per hour (37 mph).