At the end of the 1960s the US Army entered into a joint program with the Federal Republic of Germany to create a universal main battle tank for combat in Europe against the Soviets and the Warsaw Pact. It was felt that a quantum leap forward was needed over the tanks then in service (the M60 and Leopard 1 series tanks) as the Soviets were fielding newer and more powerful tanks such as the T-62 and the “M-1967” (which turned out to be the T-64 series tanks).
The Germans offered the suspension and running gear, and the Americans offered their 152mm gun/launcher and the Shillelagh missile system then being fielded in the M551 Sheridan and M60A2 tanks. The US authorized the construction of eight prototypes, most of which were to be made of mild steel as proof-of-concept demonstrators.
Testing began at the end of 1967 at Aberdeen Proving Ground, and there were immediately problems with the technology overreach of the systems.
Finally, in late 1970 the MBT-70 project was cancelled. The Germans withdrew and began working on the Leopard 2 series tanks which emerged about a decade later. The Americans tried to come up with an austere version of the MBT-70, now dubbed the XM803, but it too failed and was terminated in June 1972.
A total of 14 prototypes were built - eight US and six German. Of the US ones, only five were completed as MBT-70s and only two of them exist today (one was finished as an XM803 and another set of parts was assembled as a “gate guard” dubbed the “Pigg Tank” at Fort Knox). Only two of the German prototypes survive, but one at Koblenz in the Deutsches Panzermuseum is intact and nearly complete as built.