A new powerpack and improved transmission gave it higher speed than the Centurion despite being heavier due to major upgrades to armour protection and the armament.
To this end the gun was to have a greater angle of depression than the 8 degrees of Conqueror and would be equipped with better frontal armour.Primary problems included cylinder liner failure, fan drive problems and perpetual leaks due to vibration and badly routed pipework.However, as the engine power improved the tank itself became heavier.The design of the Chieftain included a heavily sloped hull and turret which greatly increased the effective thickness of the frontal armour – 388 mm (15.3 in) on the glacis (from an actual thickness of 120 mm (4.7 in)) and 390 mm (15.4 in) on the turret (from 195 mm (7.7 in)).It had a mantletless turret in order to take full advantage of reclining the vehicle up to ten degrees in a hull-down position.The gearbox was operated motorcycle-style with a kick up/kick down "peg" on the left, which actuated electro-hydraulic units in the gearbox, the accelerator cable was operated by the right foot.
In the turret, the loader was on the left and the gunner on the right of the gun with the commander situated behind the gunner.
The commander, gunner and loader were situated in the turret.
To the left side of the turret was a large searchlight with infra-red capability in an armoured housing.
For security reasons early prototypes had a canvas screen covering the mantlet and a sheet metal box mounted over the sloping glacis plate to disguise the configuration of the vehicle.
The driver lay semi-recumbent in the hull when his hatch was closed down which helped to reduce the profile of the forward glacis plate.
The Chieftain was an evolutionary development of the successful cruiser line of tanks that had emerged at the end of the Second World War.