Staff Writer (Updated: 2/14/2016):
By this time in history, there proved general concern by NATO parties in the capability of existing Western guns when penetrating the IS-3's stout armor protection at range and, thusly, the United States and Britain both undertook programs to remedy the situation, this providing the basis for the "M103" and "Conqueror" designs respectively. IS tanks (generally referred to as "Josef Stalin" tanks) were born from the fighting of World War 2 which pitted Soviet armor against an invading German force. The IS-1 combined heavy armor protection with a massive 122mm main gun and proved more than a match for all available German tanks of the time. The IS-1 was debuted in 1943 and this was followed by the improved IS-2 in April of 1944. The IS-3 represented a late-war upgrade to the IS-2 line and saw its armor configuration revised for the better with a new cast hemispherical turret instituted. However, availability of the IS-3 during the waning months of World War 2 was restricted and, thusly, the tank missed out on combat actions in Europe altogether. Regardless, the IS-3 remained the staple Soviet heavy tank in the early Cold War years that followed. A modernized version appeared in 1960 as the "IS-3M".
The Conqueror was derived from a British Army design direction that sought use of a logistically-friendly "universal chassis" intended to form the future of British armored forces. The universal family concept was designated as "FV 200" and would have incorporated several combat tank forms, a self-propelled gun design and a turretless armored personnel carrier. To go along with the universal chassis, a new heavy turret was developed to house a powerful 120mm main gun. Manufacturer of the vehicle was undertaken by the Royal Ordnance Factory out of Dalmuir beginning in 1955 as the "Tank, Heavy No. 1, 120mm Gun, Conqueror, Mk I". Only twenty Mk I vehicles were completed before production switched to the revised "Mk 2" and these saw deliveries peak at 165 units, The final Conqueror Heavy Tank was completed in 1959 and many were shipped to Europe to serve in the "British Army of the Rhine" (1945-1994) stationed in Germany during the Cold War (1945-1991).