The U.S. Army M551 "Sheridan" AR/AAV (Armored Reconnaissance/Airborne Assault Vehicle) Amphibious Light tank. Produced from 1966-1970/in service under various forms, from 1969 - 1997.
This light tank was used by mostly airborne units and was usually dropped on a skid from a transport aircraft. The crew would not be in the tank when it was dropped off).
The armor was an aluminum alloy and steel. The tank weighed about 15 tons. The main gun varied, but the most common was the M81E1 152mm grenade launcher.
Top speed: Road: 43mph/69 km/h Swimming: 3.6 mph/5.8km/h. This tank failed because of unreliability and thin armor.