We can trace the roots leading to the development of the Chieftain main battle tank right back to the last days of the Second World War and Britain's first mass-produced "universal tank" (no longer a cruiser or an infantry tank), the Centurion. In the early 50s, Britain – still ravaged by the impact of a victorious but costly war – was looking to improve the firepower of its tank forces (preferably at a bargain price). The first step towards the new tank was a memorandum requiring the development of Medium Tank No.2 (No.1 was the FV 221 Caernarvon, derived from the Conqueror). It was supposed to be an entire family of weapon system to enter service in 1956 (which naturally turned out to be too optimistic).
Reality – as is often the case – clashed with the well-laid plans and the road to the new successful tank was long and paved with dead ends.