In Europe, the US Army fielded only one battalion of heavy tanks, from January 1958, originally assigned to the 899th Tank Battalion, later re-designated the 2d Battalion, 33d Armor.
The US Army heavy armor battalion, in contrast to other armor units, was organized into four tank companies, composed of six platoons each, of which each platoon contained three M103s, for a total of 18 tanks per company.
Standard US Army armor battalions at the time had three companies per battalion, each with three five-tank platoons, with 17 tanks per company (two tanks were in headquarters platoon).
The US Marine Corps assigned one M103 company to each of its three Marine tank battalions, including its Marine reserve units.
The M103 was never used in combat.

While the US Army deactivated its heavy armor units with the reception of the new M60 series main battle tanks in 1963, the remaining M103s stayed within the US Marine Corps inventory until they began receiving the M60 series main battle tank.
With the disappearance of the heavy tank from US forces came the full acceptance of the main battle tank in 1960 for the US Army, and 1973 for the US Marine Corps.
In Europe, the US Army fielded only one battalion of heavy tanks, from January 1958, originally assigned to the 899th Tank Battalion, later re-designated the 2d Battalion, 33d Armor. The US Army heavy armor battalion, in contrast to other armor units, was organized into four tank companies, composed of six platoons each, of which each platoon contained three M103s, for a total of 18 tanks per company. Standard US Army armor battalions at the time had three companies per battalion, each with three five-tank platoons, with 17 tanks per company (two tanks were in headquarters platoon). The US Marine Corps assigned one M103 company to each of its three Marine tank battalions, including its Marine reserve units. The M103 was never used in combat.
While the US Army deactivated its heavy armor units with the reception of the new M60 series main battle tanks in 1963, the remaining M103s stayed within the US Marine Corps inventory until they began receiving the M60 series main battle tank. With the disappearance of the heavy tank from US forces came the full acceptance of the main battle tank in 1960 for the US Army, and 1973 for the US Marine Corps.
M103 (heavy tank)