The M55 self-propelled howitzer was an American development of the 1950s. The vehicle was developed based on the commonality of automotive parts with the existing series of M46 and M47 Patton medium battle tanks, which were in service with the United States during the Cold War. The M55 was similar in scale and function to the earlier M53 self-propelled assault gun, armed with a 155mm main barrel. However, the M55 used the much larger 203.2 mm M47 howitzer, which limited the total amount of ammunition due to the heavier shells. During the 1950s, the M55 was produced by the Pacific Car & Foundry Company. Many US Army M53 systems were then upgraded to the M55 standard. Some M55s were used during the American involvement in the Vietnam War (1955-1975), although they were withdrawn from the inventory over time.
