The Chieftain Mk 5 is an updated version of the British second-generation main battle tank that was used by the United Kingdom's armed forces in the 1960s and 1970s. Developed by Leyland Motors, it was produced from 1965 to 1983. With its combination of high firepower and strong armor protection, the Chieftain was one of the most powerful Western tanks of its time. It was also the first tank with a semi-reclining driver’s seat, a design feature that significantly reduced its overall height. A total of 2,265 tanks of all modifications were produced. In 1971, the tank was upgraded to the Chieftain Mk.5 standard, which featured a new 760 hp engine, an electronic ballistic computer, and passive night vision devices.

The Chieftain Mk 5 was introduced in Update 1.69 "Regia Aeronautica". Despite the installation of the new 760 hp engine, the tank’s mobility remains insufficient. The hull has a vulnerable lower frontal plate that can be penetrated by a lot of tanks. The lack of a HEAT round in the ammunition loadout is not a serious issue because the L15A3 APDS round allows the tank to penetrate all opponents it encounters with its 300 mm of penetration.