The M551 "Sheridan" was not a light tank. The U.S. Army dropped the designations of light, medium and heavy tanks in 1960. Therefore the M551 became an AR/AAV. This stood for Armored Reconnaissance/ Airborne Assault Vehicle - you know a light tank that could be dropped from a big cargo plane like a C-130 Hercules. The process was called LAPES for Low Altitude Parachute Extraction System. A C-130 would come in at about 20 feet and slide the Sheridan out the back ramp on a pallet and a parachute would deploy to slow it down as it skidded to a stop. A pal of mine with the 82nd Airborne Div. said it was pretty cool. The Sheridan served in Vietnam and had a mixed reputation. On the plus side its light weight (15 tons) meant it didn't get stuck in rice paddy mud as much as the heavier M48 mediums did in Vietnam. The Sheridan could go right along with the infantry and provide direct fire support with caseless 152mm HE or canister rounds. (M3 and M5 "Stuart" light tanks served in the same role during WWII.) The negative side of the 152mm gun was the caseless ammo falling apart with the warhead breaking off from the propellant charge when loading. The damaged round was tossed on the floor of the tank where it was a hazard if the Sheridan rolled over a mine. The body of the tank was aluminum and had the same vulnerability problem as the M113 personnel carrier to mines and RPGs - both tended to burn furiously. The Sheridan took quite a few casualties in Vietnam despite field modifications like more armor on the underside. It was a reliable vehicle and there was nothing like it for the airborne troops so it stayed in service through Operation Desert Storm. The army retired the M551 in 1996. The photo was taken at the First Division Museum at "Cantigny" in Wheaton, Illinois. More on this wonderful place later.