Chieftain

The FV4201 Chieftain was the primary main battle tank (MBT) of the United Kingdom from the 1960s into the 1990s. Introduced in 1967, it was among the most heavily armed MBTs at the time, mounting a 120 mm Royal Ordnance L11 gun, equivalent to the much larger specialist heavy tanks in service. It was also among the most heavily armoured, with up to 195 mm (7.7 in) that was highly sloped to give 388 mm (15.3 in) thickness along the line of sight.
A development from the Centurion MBT, the Chieftain introduced the supine (reclining) driver position to British design allowing 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; this allowed it to replace both the Centurion and Conqueror heavy tank while performing their roles effectively.
The multi-fuel engine proved to be the design's primary drawback, causing frequent breakdowns; it was said sarcastically that the Chieftain was extremely effective if it broke down in a useful location. This led to a series of improved models with new armour, sensors, engines and suspension systems, and...