MGM-51 Shillelagh - The Sheridan

The Sheridan

The M81/MGM-51 was first installed on the M551 Sheridan. The Sheridan was a light aluminum-armored AFV designed to be air transportable and provide antitank support for airborne forces. In 1966 the US Army began pressing General Westmoreland to field the tank in South Vietnam, but he declined, stating that with no main gun ammunition, the Sheridan was basically nothing more than a $300,000 machine gun platform. In 1968 152mm main gun ammo became available, and the M551 General Sheridan was deployed to South Vietnam for combat operations in January 1969. Shillelagh missiles did not prove to be a problem in the Vietnam War: they were not used.

The Sheridans' 152mm main guns were used in combat operations in Vietnam but proved troublesome. The combustible casings of the 152mm caseless ammunition rounds did not burn completely, requiring a complicated and slow gas-driven scavenging system. They were also liable to cook off if the vehicle were hit. Firing the gun caused such a large recoil as to result in failures in the delicate missile firing electronics on the tank. These problems, in combination with the lack of suitable targets, resulted in the Sheridan's deployment to South Vietnam without the complex missile system.

The Shillelagh was considerably larger than a conventional round, so only a small number could be carried. Typical loads consisted of only 8 missiles and twenty M409 HEAT rounds for short-range use. In addition the missile proved to have a very long minimum range. Due to the layout of the vehicle, the missile did not come into the sight of the gun/tracker system until it was 800 yards (730 m) from the vehicle, at which point it could start to be guided. Because of its maximum range of about 2,200 yards (2,000 m), the system was only effective within a fairly narrow span of combat distances.

While the maximum range of 2,200 yards (2,000 m) was acceptable, the Army felt it could and should be improved. Ford received a contract to develop a longer range version in 1963, and returned a slightly larger design the next year. Test firing of the new MGM-51B started the next May, and production began in October 1966. Besides the changes to the missile, the gun was modified. In testing it was found that the key slot in the gun led to cracking after firing only a few shells. After further study a version with a shallower slot and new barrel was selected, creating the M81E1/MGM-51C.

The new missile was about 45 inches (1,100 mm) long, about 6 inches (150 mm) in diameter, and weighed 60 pounds (27 kg). It remained in production until 1971, by which time 88,000 had been produced, probably in anticipation of use by main battle tanks (below). Nearly a half dozen missiles fired at bunkers by Sheridans during Operation Desert Storm (Iraq/Kuwait) in January and February 1991. This was the only time the missile system was fired in combat.