MBT-70

The MBT-70 or German Kampfpanzer 70 was a 1960s German-U.S. joint project to develop a new main battle tank, which was to be equipped with a number of advanced features. It utilized a newly developed hydropneumatic "kneeling" suspension and housed the entire crew in the large turret. The MBT-70 was armed with a 152 mm XM-150 gun/launcher, which could use conventional ammunition and the Shillelagh missile for long range combat.

The MBT-70's main armament was a stabilized XM-150 152 mm gun/launcher, a longer-barreled and improved variant of the XM-81 gun/launcher used in the light M551 Sheridan and the M60A2 'Starship'.
This gun/launcher could fire conventional 152 mm rounds like High Explosive, anti-personnel, High Explosive Anti-Tank (HEAT) and Armor Piercing Fin-Stabilized Discarding Sabot (APFSDS) rounds, but also the Shillelagh missile, a 152 mm guided missile, which had a combat range of some 3,000 meters.

The secondary armament of the MBT-70 consisted of a remote-controlled 20 mm autocannon for use against aircraft and light armoured vehicles. This was the M139, a US-made version of the Hispano-Suiza HS.820 that was a feature of most 1960s US Army vehicle designs. The gun could be retracted into a container behind the driver's rotating cupola for protection as well as to reduce overall height, and was operated remotely by the commander. Furthermore a 7.62 mm machine gun(MG3) was mounted coaxially alongside the main gun for close-defense.

In 1969 the project was well over budget and the Germans withdrew from the effort, developing a new main battle tank on their own instead (the Leopard 2). In the US the development continued for a short time, until in 1971 when Congress cancelled the program. The MBT-70 is the "grandfather" of the Leopard 2 and the M1 Abrams, the current main battle tanks of both countries.

with its XM-150 152 mm gun/launcher and 20 mm L/86 (L/85) HS 820 autocannon

Photo is taken in German's Panzermuseum Munster!