M103 heavy tank The M103 heavy tank served the United States Army and the US Marines during the Cold War . Until the development of the M1 Abrams in the mid - 1970s , it was the heaviest and most heavily armed tank in US service . The M103 was manufactured at the Detroit Arsenal Tank Plant and the first units were accepted in 1957 . The last M103s were withdrawn from service in 1974 . Design and development . Like the contemporary British Conqueror tank , the M103 was designed to counter Soviet heaviy tanks such as the Josef Stalin tank or the T - 10 if a conventional World War III broke out . Its long - ranged 120 mm cannon was designed to hit enemy tanks at extreme distances . In 1953 - 1954 a series of 300 tanks , initially designated T43E1 , were built by Chrysler at the Newark plant . Testing was unsatisfactory , with the tanks entering storage in August 1955 . After improvement recommendations , on 26 April 1956 the tank was designated the M103 Heavy Tank . Of the 300 T43E1s built , 80 went to the US Army ( 74 of which were rebuilt to M103 standard ) , and 220 were accepted by the US Marine Corps , to be used as infantry support , rebuilt to improved M103A1 , then M103A2 standards . The successive versions of the M103 shared many components with the M47 and M48 Patton tanks and the M60 which , with the exception of the M60 ( a main battle tank ) were all considered 90 mm gun ( medium ) tanks . Tracks , rollers and suspension elements were the same , with some modification to take into account the greater weight . The engine and transmission were never modified enough to give the extra power needed for the greater weight of the M103 , and as a result , the tank was relatively underpowered and the drive systems were fragile . The turret of the M103 was larger than that of the M48 or the M60 to make room for the huge 120 mm gun and the two loaders assigned to it , in addition to the gunner and the commander . The driver sat in the hull . The gun was capable of elevation from + 15 to - 8 degrees . Armor . The armor is made from welded rolled and cast homogeneous steel of varying thickness . Service . In Europe , the US Army fielded only one battalion of heavy tanks , from January 1958 , originally assigned to the " 899th " Armor , later redesignated the " 2 / 33rd 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 M103 ' s , 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 3 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 tank s 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 . Although the 21st century ' s M1 Abrams main battle tank utilizes the same caliber of main gun , the 120 mm , the M103 ' s cannon was a rifled gun firing a fixed round , ejecting a lengthy brass shell casing ( 34 . 69 inches in length for the armor - piercing rounds ) . The M1 tank ' s 120 mm main gun is a smooth bore firing a semi - caseless round , ejecting only a back cap of the original loaded round ; the bulk of the 120 mm shell ' s casing is consumed during firing . Ammunition fired by the M103 ' s M58 cannon included : Surviving examples . M103 at Ft . LewisThere are several M103s in existence including the late M103A2 version .