The Chieftain was an evolutionary development of the successful cruiser line of tanks that had emerged at the end of the Second World War. Its predecessor, the Centurion main battle tank (MBT), is widely considered to be one of the most successful of post-war MBT designs. However, the introduction of the Soviet IS-3 /IS-4 heavy tank along with Soviet T-54/T-55 forced the introduction of their own Conqueror heavy tank armed with a gun. A single design combining the firepower of the Conqueror's 120 mm gun with the mobility and general usefulness of the Centurion was seen as the ideal combination.