M31 Centurion-to M1A5 Chariot
Hmmmm
How about Britain and the US agree during the war to develop a heavy Universal tank in 1942 based on experiances
Britain Proposes the Centurion with a 17 pounder gun (76.2mm) and later a 20 pounder gun (84mm) in 1944 and 1945
The US Test these tanks agaisnt the Early T26 Pershing familiy of tanks armed with 76mm and 90mm guns and find the British tanks to be more 'mobile' and the 20 pounder gun to be a superior hole puncher
The Americans modify a early Cent with a more powerful US Engine and Gearbox as well as fit a commanders copula with a 50 cal HMG and this tank with the 20 pounder is chosen as the Universal tank design.
The US Made M31 "Centurion" Mk2 Enters service with the US Army in 1947 and British Built versions of the tank replace Earlier Centurions in British Service in 1949 after British Factories Re-tooled to build it.
The Tank proved to be rugged and capable of amazing feats of Cross country Mobility when used in fighting in Korea in 1951-56.
A 'Heavy' Version of the Tank the M31A4 or Conqueror in British Service enters production in 1953 and mounts the 120mm M58 Gun - intended to match the IS3 heavy tanks then in Russian Service - the turret and gun were beset with problems though out the service life of this varient.
This version of the tank was very similair to the 84mm armed version except it had a larger turret designed to accomodate the larger gun and ammo.
The most famous verison is of course the M31A7 or Centurion 7 that started production in 1957 with the deadly 105mm L7 / M68 Rifled gun that was designed to fit into the same space as the existing 20 pounder gun and intended to allow all existing tanks to be retorfitted and subsequant tanks to be armed with all in order to defeat the then Brand new Russian T54/55 tank - which the 20 pounder gun would have struggled to defeat.
This version of the tank was effectively different from the first Centrions - Powerplant, gearbox, Armour, weapons (including deletion of the oversized commanders copula), sights and suspension where all different - however both Britain and the US kept the name.
It was this tank and upgunned earlier varients that allowed the Indian Army in 1964 and 1972 to defeat the Russian and Chinese supplied Pakistani tanks and the Isrelies to handily defeat pretty much all of their Neighbours in both 1969 and 1972.
However by this point the design had reached its zenith and even the 40 ton version mounting an improved 120mm gun was not going to match the expected new Russian tanks (T73 and T80) - thought to start arriving within 5 years.
So designers from the US, Britain along with those Indian and Isrelie companies involved with updating the design in their armed forces collaborated on a design called the XM1 Chariot.
This would innitially mount the improved rifled 120mm L11 (M75) main gun
By 2015 this tank - now in its 5th MK would still be in production in Britain, USA, India and Israel - mounting a crewless Turret with a German Designed 140mm CTA smoothbore auto loading main gun.