The FV4201 Chieftain was the main battle tank of the United Kingdom during the 1960s, 1970s and 1980s. The main battle tank was further improved by being the first tank in service to incorporate the Chobham armour upgrades.
A development of the Centurion, the Chieftain introduced the supine (reclining) driver position to British design enabling a heavily sloped hull with reduced height. 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. It remained in service until replaced by the Challenger 1 which shared a large number of the Chieftain's features.
Source: Wikipedia, "Chieftain (tank)", available under the CC-BY-SA License.