The M551 Sheridan Light Tank had a checkered career during its service with the United States Army. You can read the details here, but the BLUF is that the M-551 Sheridan was envisioned as a lightweight aluminum, air transportable tank. It was equipped with a massive 152mm short barreled main gun that could fire anti-tank missiles in addition to conventional rounds that could defeat any known armored system at the time. It was a good idea in theory, but that was about as far as it went. The anti-tank missile never proved practical and the cumbersome one piece shells for the 152mm main gun were prone to split in two, spilling large amounts of propellant inside the tank which could lead to an internal explosion. The M551 Sheridan proved invaluable in Vietnam as its light weight allowed it to traverse mud better than most vehicles but suffered from a low rate of fire in combat. This resulted in the M551 Sheridan spending much of its time as a tow truck pulling heavier vehicles out of the mud as the tropical humidity tended to short circuit its electrical firing system.
After Vietnam, the U.S. Army had large numbers of Sheridan light tanks available that only airborne units wanted. There were proposals to scrap the M551 Sheridan program but cooler heads prevailed and in 1980, the bulk of the M551 Sheridan light tanks were sent to the National Training Center (NTC) at Fort Irwin, California. The NTC was tasked with providing realistic ground training to U.S. Military units that involved simulated tank on tank armored combat in a desert environment. This was an early recognition that many of the U.S. Military’s future battles would be in the Middle East. The M551 Sheridan was an ideal vehicle to form the nucleus of the Soviet opposition force (OPFOR) and early exercises had the Sheridan’s operating in conjunction with local infantry from Army and United States Marine Corps units to test the combat effectiveness of U.S. and NATO Military units from around the world.
One of the early changes made to the M551 Sheridan was to make the tanks look more like the Soviet made equipment that the U.S. Military would encounter in the Middle East. Some of these changes were as simple as replacing the 152mm main gun with a fake barrel to make the vehicle look like a Soviet BMP-1. But other changes were as radical as adding fiberglass body panels so that a Sheridan light tank looked like a Soviet T-72 main battle tank. Each tank was equipped with sensors to pick up laser signals indicating if the vehicle had been hit by a simulated round. A red light on the tank would light up to indicate a kill.
The combination of highly experienced Sheridan tank crews with infantry that practiced a radical form of combined arms maneuver warfare shocked many of the early units that went to the National Training Center. Exercises would be repeated until the visiting unit could master the OPFOR and this highly realistic training did much to prepare the U.S. Military for the 1991 Gulf War. The Soldiers and Marines who went to Kuwait and then into Iraq found themselves fighting an enemy less capable than the one they had been fighting in the Mojave desert for the previous decade.
The M551 Sheridan was retired in 2003 from the NTC, but it did get it’s day in the sun. During the 1991 Gulf War, there was concern that the Iraqi Republican Guard would cross the border into Saudi Arabia. This led to a hasty deployment of U.S. Army airborne forces with their Sheridan light tanks which then deployed along the border. The reality was that the M551 Sheridan wouldn’t have fared well against an Iraqi T-72, but that was something the Iraqi Army didn’t know. The sudden appearance of large numbers of American Sheridan light tanks along the Saudi Arabian border was enough to cause the Iraqi Army to pause and gave the Allied coalition enough time to mass sufficient forces in Saudi Arabia to prevent an invasion. For the second time in its career, the M551 Sheridan proved its worth by never firing a shot in anger.