Key Points and Summary – The M551 Sheridan was a unique US Army light tank, officially an Armored Reconnaissance/Airborne Assault Vehicle, known for its amphibious capability and, most notably, its ability to be dropped by parachute.
-Armed with a powerful but problematic 152mm gun that could fire conventional rounds and Shillelagh anti-tank missiles, it saw extensive but difficult service in Vietnam, where its thin aluminum armor made it vulnerable to mines and RPGs.
-After being phased out of most units, it found a new life with the 82nd Airborne Division, famously conducting a combat parachute drop during the 1989 invasion of Panama.
M551 Sheridan Was the Flying Light Tank Thanks to Air Drops:
While designated as an AR/AAV or Armored Reconnaissance/Airborne Assault Vehicle, the M551 Sheridan was actually an Army light tank. It was amphibious and could swim rivers at 3-4 mph.
The most interesting thing about the Sheridan was that it could be dropped by parachute, which gave it a much longer service life as the only organic armor in the 82nd Airborne Division.
The Sheridan was named after General Phillip Sheridan, the Union Army’s outstanding cavalry commander during the Civil War. Originally designed as an armored reconnaissance vehicle for cavalry units, it saw extensive action in Vietnam and has a checkered history there.
Pros of the M551 Sheridan
It was more mobile than the M48 Patton tanks, better armored than theM113 armored personnel carriers it was replacing, had good cross-country mobility, and was fast. The Sheridans could race at 43 mph. Cadillac made the vehicle.
So, what young tanker wouldn’t want to tool around Vietnam with a Caddy that touted a 152mm main gun?
The Sheridan did pack a punch. Its M81E1 Rifled 152-mm main gun carried 20 rounds and eight to nine MGM-51 Shillelagh missiles.
This armament could defeat any known armor and destroy bunkers and built-up positions. The weapon also fired M625 canister rounds loaded with thousands of flechettes, which decimated light Viet Cong infantry during the battles of Tay Ninh and Bien Hoa.
The M551 also carried a .50 caliber heavy machine gun and a 7.62mm GPMG in the turret.
Cons of the Sheridan
Troops distrusted the Sheridan before it arrived in South Vietnam because of its lack of armor. The hull was made of aluminum and was very thin. The steel turret also lacked thick armor. Therefore, the Sheridan was highly vulnerable to anti-tank mines and rocket-propelled grenades, which were the favorite weapons of the Viet Cong and North Vietnamese regulars.
The vehicle also had a significant issue with 152 mm ammunition. The round was attached to the propellant charge, which was combustible, and many times, the projectile separated from the combustible case during loading. Therefore, the tank’s crewmen were trained not to load the round.
Because the turret housed the highly combustible propellent charge, the crews knew to abandon the vehicle at the first sign of fire or smoke inside the tank.
The Sheridan’s rate of fire could have been faster: only about two rounds per minute, while a well-trained M48 crew could fire 18-19 rounds per minute. Another issue was that the tank was light (15 tons).
The front of the tank rocked upward when the main gun was fired, and many times, the commander in the open hatch was injured by the hatch ring when rocking backward.
The Sheridan Parachutes Into Panama, 1989
The Army began phasing out the Sheridan in 1978, but the 82nd Airborne had a use for them as deployable armor for the division. In 1988, when the 82nd deployed to Honduras during “Operation Golden Pheasant,” Sheridans were deployed but airlanded during the brief Nicaraguan “invasion.”
In 1989, however, the Sheridan earned its combat jump wings. During the invasion of Panama, the 82nd jumped on Tocumen airport. The unit dropped 10 Sheridans via C-141 Starlifter aircraft. These were part of C Co. 3/73 Armor.
The Army secretly brought in four more before the invasion via C-5 Galaxy aircraft at Howard Air Force Base.
The Sheridans received high marks in Panama due to the Panamanian military having primarily small arms and generally having no stomach for the fight against armor.
Later, the Army deployed the Sheridan in Operation Desert Shield/Desert Storm in 1990-91. Due to its thin armor, it saw action but was limited to a flanking reconnaissance role. There, it fired the Shillelagh missiles for the first and only time in combat.
Once again, Sheridan tanks received high marks.
Retirement of M551
The Sheridan finally retired from the 82nd Airborne in 1996. No replacement has yet come forward for the Sheridan (The M10 Booker was cancelled, but don’t call it a light tank, sorry), and the light airborne division could use one.
But for now, the paratroopers are better off using Javelin missiles for anti-tank defense.
About the Author
Steve Balestrieri is a National Security Columnist. He served as a US Army Special Forces NCO and Warrant Officer. In addition to writing on defense, he covers the NFL for PatsFans.com and is a member of the Pro Football Writers of America (PFWA). His work was regularly featured in other military publications.
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