The M551 Sheridan was developed to provide the US Army with a light armored reconnaissance vehicle with heavy firepower. The main armament consists of an 152mm M81 gun/missile launcher capable of firing conventional ammunition and the MGM-51 Shillelagh antitank missile (20 conventional rounds and 8 missiles). Due to problems with the gun-tube-launched antitank missile, the Sheridan was not fielded widely throughout the Army. The gun would foul with caseless ammuniton, gun firing would interfere with missle electronics, and the entire vehicle recoiled with unusual vigor when the gun was fired, since the 152mm gun was too big for the light-weight chassis. The Shillelagh missles were evidently never used in anger. In addition to the main gun/missile launcher, the M551 is armed with a 7.62mm M240 machine gun and a 12.7mm M2 HB antiaircraft machine gun. A Detroit Diesel 6V-53T 300hp turbo-charged V-6 diesel engine and an Allison TG-250-2A poweshift transmission provide the Sheridan's power. Protection for the four-man crew is provided by an aluminum hull and steel turret. Although light enough to be airdrop-capable, the alumninum armour was thin enough to be pierced by heavy machine-gun rounds, and the vehicle was particularly vulnerable to mines.
Initially produced in 1966, the M551 was fielded in 1968. 1,562 M551s were built between 1966 and 1970. The Sheridan saw limited action in Vietnam, where many deficiencies were revealed. The missle system was useless against an enemy that employed tanks, though the Sheridan saw a lot of use towards the end of the war because of its mobility. Sheridan-equiped units participated in Operation Just Cause in Panama (1989), and was deployed to Saudi Arabia during Operation Desert Shield. As projectile technology advanced, the Sheridan's potential declined and it was phased out of the US inventory beginning in 1978. However, the M551 is still used by the 82nd Airborne Division. Some 330 "visually-modified" Sheridans represent threat tanks and armored vehicles at the National Training Center in Fort Irwin, California.
Weight (pounds) 17 tons Length 22'4" Width 13'6" Height 12'6" Forward speed 45 mph Reverse speed 10 mph Engine Detroit Diesel 6V-53T 300-hp water cooled turbocharged 2-stroke V-6 diesel.
Allision TG-250-2A powershift cross drive transmission with 4 forward /1 reverse
Vertical obstacle climb 49 in Maximum width ditch 108 in Fording Depth 48 in Main Gun 152mm cannon/Missile Launcher with 20 HEAT-T-MP rounds and 8 Shillelagh missile rounds Coaxial machinegun M240 - 7.62mm Commander's machinegun M2 - .50 cal Sensors and Fire Control M129 gunner's telescope, magnification 8x 8° field of view (FOV), M44 gunner's IR night sight magnification 9x6° FOV, IR SACLOS data link