MBT-70 thumb|left|MBT-70 prototype test firing an MGM-51 The most ambitious project based on the Shillelagh was the MBT-70, an advanced US–German tank. Design work on the MBT-70 began in 1963. The tank mounted a huge auto-loader turret on top of a very short chassis, so short that there was no room for a driver in the front hull. Instead of being located in the conventional position, the driver was seated in the turret with the other crew members, in a rotating cupola that kept him facing forward. The gun was a new longer-barreled design, the XM-150, which extended range and performance to the point where it was useful for sabot type rounds as well. However, the project dragged on, and in 1969 the estimated unit cost had risen fivefold. Germany pulled out of the project. The Army proposed a "cut-down" version of the system, the XM-803, but Congress cancelled it in November 1971. It initiated and issued funds to the M1 Abrams project the next month. The M1 design incorporated a conventional gun.
MBT-70 thumb|left|MBT-70 prototype test firing an MGM-51, The most ambitious project based on the Shillelagh was the MBT-70, an advanced US–German tank. Design work on the MBT-70 began in 1963. The tank mounted a huge auto-loader turret on top of a very short chassis, so short that there was no room for a driver in the front hull. Instead of being located in the conventional position, the driver was seated in the turret with the other crew members, in a rotating cupola that kept him facing forward. The gun was a new longer-barreled design, the XM-150, which extended range and performance to the point where it was useful for sabot type rounds as well. However, the project dragged on and in 1969 the estimated unit cost had risen fivefold. Germany pulled out of the project. The Army proposed a "cut-down" version of the system, the XM-803 but Congress cancelled it in November 1971. It initiated and issued funds to the M1 Abrams project the next month. The M1 design incorporated a conventional gun.