The Ford MGM-51 Shillelagh was an American anti-tank guided missile designed to be launched from a conventional gun (cannon).

Developing a system that could fire both shells and missiles reliably proved complex and largely unworkable for the United States.

Western forces largely gave up on the gun-launched missile concept, although it remains in use on former Soviet Union designs.

To overcome this potential difficulty, the US Army began to favor high-explosive anti-tank (HEAT), or shaped charge rounds in the 1950s.

The US Army sought to overcome this problem by developing guided missiles that had shaped charge warheads and were accurate beyond a few hundred yards.

In 1958, the Army thought that existing knowledge was sufficient to begin work on a guided missile with a HEAT warhead, and in June 1959 Sperry and Ford Aeronutronic were asked for designs to fill the shorter range role.

The Sheridan was a light aluminum-armored AFV designed to be air transportable and provide antitank support for airborne forces.

[7] In 1968, 152 mm main gun ammo became available, and the Sheridan was deployed to South Vietnam for combat operations in January 1969.

[7] The combustible casings of the 152 mm caseless ammunition rounds did not burn completely, requiring a complicated and slow gas-driven scavenging system.

Ford received a contract to develop a longer range version in 1963, and returned a slightly larger design the next year.

The Army had originally started development of a low-profile turret with a short barrel for their existing M60 tanks in the 1960s, but did not place an order for delivery until 1971, when the main problems with the system had been resolved.

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.