The M-551 Sheridan light tank was built to meet a 1959 Army requirement for an armored reconnaissance airborne assault vehicle (ARAAV) to support airborne units. Enemy tanks are the biggest threat to para- troopers in the early stages of operations. The Army wanted an armored vehicle that could defeat tanks and that could be airdropped or airlanded in support of their paratroopers.

The problem, of course, is evident. The best way to defeat a tank is with another tank, Unfortunately tanks are, by their nature, heavy. Heavy tanks require large planes to carry them, and large planes require large airfields to land. Airdropping tanks is possible, but there is a limit to the size a parachute can hold. Thus, armored reconnaissance airborne assault vehicles have to be as light as possible. The only way to lighten a tank is to take off the armor. That, unfortunately, doesn't leave much of a tank.

The Allison Division of General Motors put forth several innovative proposals to meet the Army requirement in 1960. They were given a contract to build the prototype of the XM-551 Sheridan light tank. The new tank was 20'8" long, 9' wide and 9'8" high. The hull was made of aluminum, and the turret was welded steel.

The weight-saving measures and small size gave the tank a combat weight of 34,898 lbs. It was armed with a 152mm dual-purpose gun that could fire a conventional 152mm round or launch the Shillelagh missile. The tank was powered by the six-cylinder Detroit Diesel, which gave it a top speed of 45 mph and range of 373 miles.

This tank was, at best, a compromise. It did not have great armor protection nor a tremendously powerful gun. However, it could be quickly airlifted by any of the USAF's transport airplanes; and, when deployed in a defensive position, it could destroy enemy tanks and armored personnel carriers. Unfortunately, the Sheridan pleased no one.

The Sheridan was too lightly armed and armored to suit the Army. In addition, it was terribly complicated and very expensive. Although the M551 was put into production in 1966 and served with airborne and armored units, it was replaced at every opportunity by the M-60 main battle tank.

The Sheridan light tank should have been a failure. But, whenever a crisis arose, the first units deployed were normally the 82nd Airborne Division or elements of the 18th Airborne Corps, and the M551 tank was still the only tank that could fly on any type of transport. The unloved Sheridan served in Vietnam, Korea, Panama, and Desert Storm and is currently on the streets of Haiti. Its career has spanned 32 years, and there is still no vehicle that can replace it.

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