The M55 was a standard U.S. Army motorized howitzer used during the 1950s and early 1960s, until it was replaced by the M110. It was largely deployed in NATO areas and was used extensively during the Vietnam era. This howitzer was designed to provide general artillery support to ground troops and close general support to armored columns. A crew of six was required to operate the vehicle. The crew was protected from both enemy fire and radioactive fallout.Serious Firepower, Serious ArmorDesigned to complement and later replace the M53 self-propelled 155MM gun, the M55 is a 203MM variant based on the Patton tank. Fitted with 25 millimeters of armor, the M55 was designed to protect the crew from indirect artillery shells, small arms fire, and radioactive fallout. The armor was designed to be light enough so it would not impede the speed of the traversing vehicle, but strong enough to withstand enemy fire.The M55 was built on the same platform as the M53 gun. The only difference between the two systems was the size and length of the barrel.The M55 was designed and manufactured by the Pacific Car and Foundry Company. Production began in the 1950s, with the first systems deployed at the end of the Korean War. The howitzer saw its first real action during the Vietnam War, and continued in service until 1969. The howitzer weighed a hefty 48.5 tons, allowing it to easily make its way through heavy brush and dense forests.By the 1970s, the howitzer had become obsolete. It began to slowly be replaced with the M107 self-propelled howitzer. Some units in Belgium continued to use the howitzer in a limited capacity through 1975, when all M55s were replaced by the M107 or M110 weapon systems.