units by 1981, and the turrets scrapped. Most of the M60A2 tanks were rebuilt as M60A3. M60A3 The development of the M60A2 with a new turret fitted with a 152mm gun was stopped and in 1978, work began on the M60A3 variant. It featured a number of technological enhancements, including smoke dischargers, a new rangefinder, and M21 ballistic computer, and a turret stabilization system. In addition, it reverted to the M68A1 105 mm cannon. All active American Army M60s eventually underwent the conversion to the A3 model. The M60A3 main battle tanks of the US Army were deployed in Operation Desert Storm in 1991 during the Gulf Crisis. The M60A3 was phased out of US service in 1997 and was replaced by the M1 Abrams main battle tank. MBT-70 The MBT-70 (German: KPz 70) was an American–West German joint project to develop a new main battle tank during the 1960s. The MBT-70 was developed by the United States and West Germany in the context of the Cold War, intended to counter the new generation of Warsaw Pact tanks developed by the Soviet Union. The new tank was to be equipped with a number of advanced features such as newly developed "kneeling" hydropneumatic suspension and housing the entire crew in the large turret, and was armed with a 152mm XM150 gun/launcher, which could use conventional ammunition and the Shillelagh missile for long range combat. By the late 1960s, the development of the MBT-70 was well over budget and affected by design issues. West Germany withdrew from the project due to costs and a new difference in requirements. The United States continued development of the MBT-70 until 1971 when the program was finally cancelled. West Germany independently developed the Leopard 2 as its new main battle tank. M1 Abrams The M1 Abrams came from the diverted funds from the over budget and impractical MBT-70 and XM815 projects. Prototypes were delivered in 1976 by Chrysler Defense and General Motors armed with a license-built 105 mm rifled cannon. The Chrysler Defense design was selected for development as the M1. In 1979, General Dynamics Land Systems Division purchased Chrysler Defense. The M1 was the first of its kind. It featured a low profile turret and for the first time ever on a tank, composite chobham armor. Despite all these advances, the Abrams still retained the 4-man crew of the M60 tank as the autoloader was