Editing MGM-51 Shillelagh (section)

=== Sheridan===
[[File:MGM-51 Shillelagh2.jpg|thumb|right|MGM-51 Shillelagh fired from a Sheridan]]
[[File:White Sands Missile Range Museum Shillelagh display.jpg|thumb|[[White Sands Missile Range]] Museum Shillelagh display]]
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]].<ref name=Starry142>Starry p. 142</ref> 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.<ref name=Starry143>Starry p. 143</ref> In 1968, 152 mm main gun ammo became available, and the Sheridan was deployed to South Vietnam for combat operations in January 1969.<ref name=Starry143/> Shillelagh missiles did not prove to be a problem in the [[Vietnam War]]: they were not used.<ref name=Starry143/>

The Sheridans' 152 mm main guns were used in combat operations in Vietnam but proved troublesome.<ref name=Starry143/> The combustible casings of the 152 mm [[caseless ammunition]] rounds did not burn completely, requiring a complicated and slow gas-driven scavenging system. They were also liable to detonate if the vehicle was 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 their deployment 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 nine 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 {{convert|800|yd|m}} from the vehicle, at which point it could start to be guided. Because of its maximum range of about {{convert|2200|yd|m}}, the system was only effective within a fairly narrow span of combat distances.

While the maximum range of {{convert|2200|yd|m}} was acceptable, the Army thought that 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 {{convert|45|in}} long, about {{convert|6|in}} in diameter, and weighed {{convert|60|lb}}. It remained in production until 1971, by which time 88,000 had been produced, probably in anticipation of use by main battle tanks (below). Although the U.S. Army denied its usage,<ref>{{Cite web |title=The United States Army |url=https://history.redstone.army.mil/desert-storm-role.html |access-date=2022-11-16 |website=history.redstone.army.mil}}</ref> it is likely that six Shillelaghs were fired against Iraqi anti-tank guns and targets during [[Operation Desert Storm]],{{sfn|Doyle|2008|p=4}} the only usage of the weapon in anger.{{sfn|Zaloga|2009|p=43}}