M551 Sheridan 11th ACR Vietnam
American Woman

In late 1952 the Army decided to begin development on a new vehicle to fill the requirement for an air transportable/ deployable light tank. In the Spring of 1960 General Motors was selected for development of the new Armored Reconnaissance/Airborne Assault Vehicle (ARAAV), designated the XM551. Production of the vehicle, now called the M551 General Sheridan, began in 1965. This vehicle weighed in at 17 tons, combat loaded. Power for the vehicle was provided by a 300 horsepower V6 water-cooled, turbo-charged diesel engine that was coupled to a six speed transmission (four forward and two reverse gears) giving the vehicle a top speed of 43 miles per hour. The 160-gallon fuel tank gave the M551 a range of 373 miles. There was a fixed fire extinguisher system for the engine compartment that could be activated by the driver or from an outside pull handle on the left side of the vehicle above the first two road wheels. The suspension system consisted of five sets of road wheels on each side mounted on a torsion bar suspension with a rear drive sprocket and front idler wheel. There were no track return rollers, and the first and last sets of road wheels were fitted with hydraulic shock absorbers. Armament consisted of a 152mm (6-inch) main gun that could fire both combustible case conventional ammunition and high explosive Shillelagh missiles. However, the missile system was not put in the M551's that were sent to Vietnam. The conventional ammunition fired from the vehicle consisted of High Explosive (HE), High Explosive Anti-Tank (HEAT), White Phosphorus (WP) and Cannister (affectionately referred to as "can rounds" by the Sheridan crewmembers). It's interesting to note that the Vietnam War brought about the invention of the Cannister round making necessity the mother of invention. The tank commander had an M2, Heavy Barrel (HB), .50 caliber machine gun to fire, and there was an M73, 7.62mm machine gun mounted coaxially inside the turret for the gunner to fire. Smoke grenade launchers that were used for cover were fitted on the underside of the forward position of the turret, but these were never used in the Vietnam War. Sheridans were sent to Vietnam in January 1969 for a field test. They were assigned to the 3rd Squadron, 4th Cavalry of the 25th Infantry Division and the 1st Squadron, 11th Armored Cavalry Regiment. This test ran for three months with several problems noted. The two biggest problems were the vehicles being severely damaged after running over mines and the conventional ammunition inside the turret rupturing and detonating after the vehicles were hit by RPGs. A partial solution for the mines was the installation of "belly armor" - titanium armor panels placed under the bow of the hull. However, there was no real solution to the RPG problem other than for the crewmen, except the driver, to ride on top of the vehicle's turret for added safety. Even with these problems M551 Sheridans were sent to all of the divisional cavalry squadrons and the rest of the 11th Armored Cavalry Regiment in Vietnam. The Sheridans saw quite a bit of action and were instrumental in racking up some high body counts. They were some of the last armored vehicles to be withdrawn from Vietnam in the early 1970's. Their last major action was during early 1971 when Sheridans from A Troop, 4/12th Cav and from the 3/5th Cav supported ARVN forces engaged in Operation LAM SON 719.