The M551 Sheridan was a light tank developed by the United States and named after Civil War General Philip Sheridan. It was designed to be landed by parachute and to swim across rivers. It was armed with the technically advanced but troublesome M81/M81E1 152mm gun/launcher which fired conventional ammunition and the MGM-51 Shillelagh guided anti-tank missile.
The M551 Sheridan entered service with the United States Army in 1967. At the urging of General Creighton Abrams, the U.S. Commander of Military Forces in Vietnam at the time, the M551 was rushed into combat service in Vietnam in January 1969. In April and August 1969, M551s were deployed to units in Europe and Korea, respectively. Now retired from service, it saw extensive combat in Vietnam, and limited service in Operation Just Cause (Panama), and the Gulf War (Kuwait).