Even though it was labeled as a failure, a piece of equipment that was too complicated to maintain properly even in the barracks, let alone in the field, M551 Sheridan Light Tank managed to play a useful role in three wars. Another thing that we need to note is that its withdrawal left a gap in the structure of the armed forces, namely in airborne units who now lack organic armor support that can be parachuted into the battlefield together with infantry.
The M551 was named after General Philip Sheridan, a commander of the Union Army of the Shenandoah. General Sheridan was famous for his use of cavalry and Pentagon planners thought that he would be an ideal namesake for the fast, light, and powerfully armed tank they had envisioned. By the time M551 entered service, the division to light, medium, and heavy tanks was considered obsolete by many armed forces in the world, including the U.S. Army, but there was a need for a fast, armored vehicle which could be used in situations where M60 Paton, with its top speed of 30 mph, was just too slow.
The program, dubbed Armored Reconnaissance/Airborne Assault Vehicle, cost $1.3 billion and resulted in an amphibious 15-ton vehicle with a top speed of 43 mph. Its armor was made of aluminum, but that was the least strange thing about it. Its main gun was a 152 mm monstrosity, able to fire both shells and anti-tank missiles. The gun could devastate infantry and buildings, but its projectile velocity was just too low to harm heavily-armored Soviet tanks of the era. For that, it carried 9 MGM-51 Shillelagh missiles.
The new light tank had its baptism of fire in Vietnam. The first batch of 200 Sheridan’s was shipped overseas in 1969. They were assigned to Third Squadron of the Fourth Cavalry Regiment and the Eleventh “Black Horse” Armored Cavalry Regiment (ACR). M551 was a replacement for older and slower M48 tanks. The first clashes with the enemy showed some glaring deficiencies of its design.
The most obvious was the recoil of the huge gun had on the light aluminum chassis. It wasn’t unusual for the front end of the tank to leap up several feet after firing the main gun. Unless the crew was strapped in, this often led to serious injuries. It also messed up its targeting computer, which needed to be reset. The semi-automatic loader was also clunky and loading those big 152 caseless shells within the confines of a small turret was a challenging task. All this led to an abysmal rate of fire of two rounds per minute. For comparison sake, an experienced crew of M48 could easily dish 12 round per minute.
But the rate of fire wasn’t the worst part. M551 lacked protection needed to survive for long on the battlefield. Lack of armor made it an easy target for Vietnamese RPG teams and mines. Add in the fact that its hull was made of flammable aluminum and it is easy to see why Sheridan’s crews suffered heavy casualties. The 12th ACR lost three vehicles due to mines in a single river crossing. The 11th ACR’s Sheridan’s fared even worse. Seven of them were lost to RPG’s in a battle of Lam Son 719. In total, over one hundred M551s were lost during the Vietnam War.
Despite all of its faults, M551 Sheridan seems to have been loved by the troops that used it. Its gun had quite the punch, especially when loaded with an M625 canister round packed with thousands of flechettes which shredded Viet Kong infantry in battles at TayNinh and Bien Hoa. The lightweight tank could also move easier through the jungle, where its heavier brethren like M48 would get bogged down. Several field modifications, like added belly armor and gun shield for the exposed .50 caliber machine gun, increased both tank and its crew’s survivability rate.
After Vietnam, Amry started withdrawing M551. Soon, they only remained in service with airborne units, which led them to their next war. In 1989, ten M551s were airdropped on Tocumen Airfield in Panama. The airdrop, conducted by the third battalion of the 73rd Armor Regiment, was the first and so far, the only tank airdrop in the history of the United States military. They made quick work of Noriega’s defenses in Panama City.
In 1990, 51 M551 of the 82nd Airborne Division were used as a part of the thin line in the desert, a deterrent against Saddam Hussein’s invasion of Saudi Arabia. They were the only tanks the US could deploy via air fast enough to prevent Saddam from gobbling up Saudi Arabia as he did with Kuwait. The deterrent worked, and it gave the Pentagon enough time to deploy heavy armor in the region. Fortunately for M551’s crews, because Iraqi tanks would have little trouble in disposing of them in the open desert.
After the First Gulf War, only M551s in service were a part of 82nd Airborne rapid reaction force, but they have also been withdrawn a few years later. Some have lingered as dummy OPFOR tanks at the National Training Center, but soon the cost of their maintenance was too much to bear, and even NTC gave up on them.
Airborne units were never given a suitable replacement for M551. Even today, they lack the organic armor support that can be airdropped. Some would argue that with modern anti-tank missiles like Javelin they don’t need it, but some tasks do require a tank. While M1 Abrams are vastly superior to M551 and can even be air deployed inside C5 cargo plane, they certainly can’t be airdropped and can’t be really considered an airborne asset.