The Chieftain Mk 10 is a late modification of the British main battle tank, which remained in service with the British Army until 1995. After the Challenger tank was adopted, it formed the backbone of the armored corps alongside the Chieftain. The goal was to extend the tank’s service life and improve its performance. The Chieftain had previously undergone several modifications aimed at improving mobility, increasing reliability, and upgrading electronic systems. However, there had never been any attempts to enhance its armor, as it had long been considered sufficient. Nevertheless, the widespread use of APFSDS rounds and HEAT projectiles led engineers to reassess the Chieftain’s protection.

In the mid-1980s, the Chieftain Mk 9 received a major armor upgrade in the form of the Stillbrew add-on armor package. The upgraded tank was designated the Chieftain Mk 10, and these armor kits were gradually installed on all tanks in service. New vehicles were delivered with the enhanced armor directly from the factory. This modification extended the service life of the Chieftain tanks by several years, and they were retired in 1995.

The Chieftain Mk 10 was introduced in Update 1.71 "New E.R.A.". It is a perfected version of the Chieftain and differs from its predecessors due to its new Stillbrew frontal turret armor, which significantly strengthens protection against early APFSDS rounds, shaped-charge projectiles, and anti-tank guided missiles. Another improvement is the new L23 APFSDS round, which can penetrate most tanks anywhere. Otherwise, it remains the same old Chieftain with limited mobility and armor for its battle rating.