Editing MGM-51 Shillelagh (section)

==Development==
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 Corporation|Sperry]] and [[Aeronutronic|Ford Aeronutronic]] were asked for designs to fill the shorter range role. Ford won the contract and started work on the '''XM13'''. The first test shots were fired in 1960, and limited production started in 1964. The missile was then known as the '''MGM-51A'''.

The basic system was quite advanced for its day. The missile body consisted of a long tube with fold-out fins at the extreme rear, which was propelled from the new M81 gun with a small charge strapped on the rear. Once clear of the gun, the fins popped open and the engine ignited. To keep the missile from spinning while in the gun due to the rifling, a small "key" fitted into a straight groove in the rifled gun. Aiming the missile was simple; the gunner simply kept his gunsight on the target, while electronics in the sighting system tracked the missile optically and sent corrections through an [[infrared|IR]] link, similarly to a TV remote control. In general the gunners were able to achieve excellent hit rates.

The main problem with the system is firing the main gun with a projectile vs. a missile.  The recoil from the gun throws all the missile optics off, limiting the use of the M551 to either anti-tank or bunker buster.

Because the system was so advanced, the development of the Shillelagh was fraught with problems. Ford Aeronutronic underestimated the complexity of the task of designing a missile as advanced as this, and there were major problems with the propellant, igniter, tracker and infrared command link of the missile.<ref name=mahnken>Technology and the American way of war. Thomas G. Mahnken. Columbia University Press, 2008. {{ISBN|978-0-231-12336-5}}</ref>