Development
The Chieftain was a radical evolutionary development of the successful Centurion line of tanks that had emerged at the end of the Second World War. The British had learned during the war that their tanks often lacked sufficient protection and firepower compared to those fielded by the enemy, and that this had led to high casualty levels when faced with the superior German tanks in World War II.
In the post war period, the British Army bolstered the Centurion with the 120 mm (4.7 in) gun Conqueror heavy tank for long range anti-tank firepower against the Soviet IS-3.
Leyland, who had been involved in Centurion, had built their own prototypes of a new tank design in 1956, and these led to a War Office specification for a new tank. The General Staff specification drew on experience of the Centurion in the Korean War and the Conqueror. The tank was expected to be able to engage the enemy at long range and from defensive positions, be proof against medium artillery. To this end, the gun was to have a greater angle of depression than the 8 degrees of Conqueror and better frontal armour. The tank was expected to achieve 10 rounds per minute in the first minute and six per minute for the following four.
The design was accepted in the early 1960s. Chieftain was designed to be as well protected as possible and to be equipped with a powerful 120 mm rifled gun. The heavy armour came at the price of reduced mobility, chiefly due to engine power limitations, which was perhaps the Chieftain's main drawback. In 1957 NATO had specified that its forces should use multi-fuel engines. The engine as introduced gave less than the planned output; improvements to the engine did not increase power to the desired value.
The early BL Engine delivered around 450 bhp (340 kW) to the sprocket which meant a top road speed of around 25 mph (40 km/h) and cross country performance was limited. Due to the cylinder linings being pressure fitted coolant leaks within the cylinder block were common, resulting in white smoke billowing from the exhaust. In the late 1970s engine design changed with the introduction of Belzona which was used to improve the lining seals. Engine output also increased with later engines delivering some 850 bhp (630 kW) to the sprocket. This meant better performance and an increased speed. However the engine was the main failing of this overly maligned vehicle, along with its rather uncomfortable Horstmann coil spring suspension that made it a challenge to drive cross country and provide the crew with a comfortable ride.
Several aspects of the Chieftain design were trialled by the production of the FV4202 "40-ton Centurion" with a reclined driver position and mantleless gun mounting.
The first few prototypes were provided for troop trials from 1959, this identified a number of changes. Changes to address engine vibration and cooling resulted in redesign of the rear hull. This increased to the design weight to nearly 50 tons and as such the suspension (which had been designed for 45 tons) was strengthened. Track pads had to be fitted to protect German roads from damage and the ground clearance increased.
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