Key Points and Summary: The M551 Sheridan served as the US Army’s primary light tank throughout the Cold War, designed for reconnaissance and airborne forces with air-drop capability.
-Its unique 152mm gun/launcher fired both conventional rounds and Shillelagh anti-tank missiles. Rushed into Vietnam service, its mobility was valuable, but critical flaws emerged: the gun system was unreliable, combustible ammunition hazardous, and thin aluminum armor highly vulnerable to RPGs and mines.
-Despite combat use in Panama and the Gulf War, these persistent issues led to its 1996 retirement without a direct replacement until the recent, also controversial, M10 Booker program emerged.
The M10 Booker Combat Vehicle proudly displays its namesake on the gun tube during the Army Birthday Festival at the National Museum of the U.S. Army, June 10, 2023. The M10 Booker Combat Vehicle is named after two American service members: Pvt. Robert D. Booker, who posthumously received the Medal of Honor for actions in World War II, and Staff Sgt. Stevon A. Booker, who posthumously received the Distinguished Service Cross for actions during Operation Iraqi Freedom. Their stories and actions articulate the Army’s need for the M10 Booker Combat Vehicle, an infantry assault vehicle that will provide protection and lethality to destroy threats like the ones that took the lives of these two Soldiers. (U.S. Army photo by Bernardo Fuller)
M551 Sheridan Was the OK Light Tank
After the end of WW2, the light tank concept was phased out in favor of Main Battle Tanks and Infantry Fighting Vehicles (IFVs) like the BMP and the M2 Bradly. One light tank design remained throughout the entire Cold War: the M115 Sheridan.
The M115 Sheridan was a light tank designed for scouting and reconnaissance missions that incorporated several experimental designs. Unfortunately, the Sheridan also had several design flaws that made it less practical, ultimately leading to its retirement.
M551 Sheridan: Development and Design
The development of the M551 Sheridan dates back to the late 1950s when the US Army sought to develop a new light tank that could be air-dropped and provide substantial firepower. The Ad Hoc Group on Armament for Future Tanks or Similar Combat Vehicles (ARCOVE) was established in 1957 to explore the potential of equipping tanks with guided missiles. This group led to the development of the XM551, which would later become the M551 Sheridan.
The Sheridan was designed to be lightweight and amphibious, capable of being transported by aircraft and swimming across water obstacles. Its hull was constructed from aluminum alloy to reduce weight, while the turret was made of steel.
The vehicle was powered by a General Motors 6V53T, six-cylinder, turbocharged diesel engine, providing 300 horsepower and allowing for a top speed of 43 mph on roads.
One of the Sheridan’s most distinctive features was its main armament: the M81E1 152mm gun/launcher. This weapon could fire both conventional ammunition and the MGM-51 Shillelagh guided anti-tank missile. Another innovative aspect was the use of combustible cartridge cases for the gun rounds, although it later proved to be problematic.
The Sheridan in Vietnam
The Sheridan was rushed into service prematurely during the Vietnam War in 1969 at the urging of General Creighton Abrams. In Vietnam, the Sheridan was used primarily for reconnaissance and support roles. Its extremely lightweight, ability to traverse difficult terrain and powerful main gun made it a valuable asset in jungle warfare. However, the Sheridan’s performance in Vietnam revealed several critical flaws.
The 152 mm gun/launcher proved unreliable, with frequent malfunctions and maintenance issues. The complex nature of the Shillelagh missile system also posed challenges, as it required significant training and maintenance to operate effectively. The Sheridan’s thin armor also made it vulnerable to enemy fire, particularly from rocket-propelled grenades (RPGs) and mines.
Despite these issues, the Sheridan did provide valuable fire support and mobility in Vietnam. Its ability to be air-dropped allowed it to be deployed quickly to provide valuable support for infantry units in remote areas. Despite its lightweight, its armor offered better protection than the M113 APC, making the Sheridan a preferable alternative to most APCs. However, the overall combat effectiveness of the Sheridan in Vietnam was limited by its mechanical and survivability issues.
Post Vietnam Service
After the Vietnam War, the Sheridan continued to serve in various capacities. It was deployed to units in Europe and South Korea, where it was used for reconnaissance and patrol duties. In Europe, it was deployed in West Germany.
The Sheridan stood guard over the Fulda Gap against potential Soviet armored advances. The Sheridan also saw action in Operation Just Cause in Panama in 1989, supporting infantry operations and providing fire support.
During the Gulf War in 1991, the Sheridan saw its final combat deployment. It was deployed with the 82nd Airborne Division. The Sheridan’s mobility and firepower were again valuable assets in this conflict. However, the same issues that plagued the Sheridan in Vietnam persisted. The 152 mm gun/launcher continued to be unreliable, and the thin armor made the Sheridan vulnerable to enemy fire, even against heavy machine guns.
Evaluating the Sheridan’s Weaknesses
While the M551 Sheridan served its purpose, many challenges prevented it from living a longer service life. The aluminum hull, while lightweight, offered limited protection against even contemporary anti-tank weapons. This vulnerability was a major concern during its deployment in Vietnam, where it was susceptible to mines and RPG attacks.
Although the M81E1 gun/launcher system was an interesting idea, it was plagued by reliability issues. The combustible cartridge cases used for the 152mm rounds were prone to misfires and other malfunctions, making it a coin toss whether the system would work as intended. Additionally, while effective in theory, the Shillelagh missile system was complex and difficult to maintain in the field.
The Army made efforts to address these issues through various improvement programs. Modifications were made to improve the reliability of the gun/launcher system, and attempts were made to replace it with a more conventional weapon. Despite these efforts, the Sheridan’s shortcomings remained a persistent problem.
The Tank the Army Still Can’t Replace
The M551 Sheridan was eventually retired from active service in 1996 without a direct replacement. The Army had planned to replace it with the M8 Armored Gun System, but this program was canceled late in its development. A modest fleet of Sheridans remained in service with the 82nd Airborne Division and the National Guard until retirement.
Overall, the M551 Sheridan was an ok vehicle. While it had some interesting designs, the Sheridan was plagued with issues that prevented it from making too much of an impact on future designs. Currently, the US Army is working on another light “tank,” the M10 Booker, another vehicle plagued with doubts and controversies. In fact, the M10 was just recently cancelled.
Boomer M10. Image Credit: U.S. Army.
About the Author:
Isaac Seitz, a 19FortyFive Defense Columnist, graduated from Patrick Henry College’s Strategic Intelligence and National Security program. He has also studied Russian at Middlebury Language Schools and has worked as an intelligence Analyst in the private sector.
