The M103 was the only US heavy tank that entered service in the Cold War and like its British counterpart, the Conqueror, was designed to take on the Soviet Il-3 and T-10s. Teething troubles with the prototypes delayed its introduction until the early 1950s but these continued thereafter, prompting US authorities to declare it unfit for service until 1957. Many of its problems stemmed from being underpowered, giving it short range and making it prone to breaking down. Nevertheless, it's 120-mm gun was the most powerful used on a US tank until the M1A1 Abrams and could fire various armor piercing and high explosive ammunition. Given the delay in its introduction, it was only in service briefly with the US Army and the US Marines (its main user) before it was replaced by the M60, by which time the heavy tank category was retired. It was never used in combat.

The prototype T43 was one among many heavy tank designs developed after the end of World War II, and the only one to eventually be placed in production as the T43E1. These were eventually retired in order to resolve its mechanical deficiencies. The result of as many as 150 modifications was the M103, which was further upgraded with a new fire control system into the M103A1. Later versions, known as the M103A2 were fitted with the same engine as the M60 (most of these being conversions). Due to the size and weight of the tank, a new recovery vehicle based on its chassis was necessary, and this was known as the M51.