Development of the Sheridan M551 began in 1959. The program is known as AR/AAV or Armored Reconnaissance/Airborne Assault Vehicle. The first prototype was built in 1962 and production began in 1966. The vehicle was named in honor of Civil War General Philip Sheridan. A total of 1,700 Sheridan M551 light tanks were built until 1970, when production was halted. The M551 Sheridan replaced the M41 tank and the M56 self-propelled weapon in service with the U.S. Army. Since 1978 Sheridan has been gradually removed from service, but the last operational vehicle was decommissioned only in 1996. Currently the U.S. Army has no real replacement for these lightweight air and amphibious tanks.
Sheridan can be dropped from the air, including falling at low altitudes. Low altitude drops are made using the LAPES extraction system. A special pallet absorbs most of the impact of the landing during the landing. This maneuver makes it possible to deliver tanks when landing is not possible and the enemy has strong air defenses. In fact sheridan is the only tank that can be used in the air in service with the U.S. Army.
The sheridan M551’s hull is welded from aluminum alloy and turret welded from steel. It was made in an attempt to save weight. The front armor protects against 20 mm steel-peddling bullets, while overall protection against bullets is 14.5 mm. The vehicle is equipped with an NBC protection system.
The M551 Sheridan light tank is armed with a fairly stable and unique M48 152 mm cannon launcher capable of firing regular projectiles and MGM-51 Shillelagh anti-tank missiles. Regular ammunition is short, fat, with flammable boxes, and should be handled with care. It has an effective shot range of 1.5 km.
These regular rounds are sufficient for an infantry support role and can even handle most contemporary main battle tanks at short distances, but have poor accuracy at longer distances. The Shillelagh anti-tank guided missile is intended to face enemy tanks at greater distances. The missile is stored in an aluminum box and has a range of up to 3 km. However due to its complex electronic systems and guidance, these missiles are almost never fired, except for crew training purposes.
Similar weapon launchers, albeit in a slightly modified form, were later used as the M60A2 main battle tank. Although the tank’s unusual operational experience reveals that the 152 mm cannon launcher is lower in range and accuracy than the 105 mm and 120 mm tank cannons, which fire regular ammunition.
The secondary armament consists of a 7.62 mm coaxial machine gun and a 12.7 mm anti-aircraft machine gun.
The vehicle has a crew of four, including commander, gunner, loader and driver.
The M551 Sheridan is powered by a Detroit Diesel 6V53T diesel engine, producing 300 hp. The vehicle was fully amphibious after preparations that lasted for two minutes. On top of the water this lightweight tank is driven by its footprint.
About 200 Sheridans were used by the U.S. Army during the Vietnam War. His combat experience reveals a number of weaknesses. These light tanks are particularly vulnerable to grenades and mines. Its weapon launchers have problems with cracks that develop after repeated shootings. The gun also has too much recoil for light vehicles. Most field units are modified to help solve the problem.
The M551A1 Sheridan was an improved version of the base vehicle. It was developed in 1971 considering operational experience of the original M551. It had improved suspension and was fitted with a laser rangefinder.
The M551 Sheridan was a very innovative light tank design, however due to its numerous faults these tanks were phased out of service. The Sheridans had been replaced in reconnaissance role with the M60A1 main battle tanks and later with the M3 Bradley armored reconnaissance vehicles. In the 1980s a new M8 Buford air droppable light tank was developed in the United States, which was intended to replace the Sheridan. However the M8 programme was canceled in 1996, leaving the US airborne forces dangerously low on firepower.