The 155mm assault gun M53 was developed with components taken from M47 Patton medium tanks during the Cold War. The M53, with its 155 mm primary gun, delivered long range support to allied positions, and its self-propelled design enabled it to travel great distances. The M53 eventually saw action with both the United States Army and Marine Corps. Pacific Car & Foundry Company was responsible for assembly. Beginning in 1956, the United States Army upgraded its M53 line to the M55. The M55 was a fully armored self-propelled artillery based on the M53 155mm assault gun. It had a 203.2 mm howitzer which could traverse 30 left or right, carrying only 10 rounds of ammunition. The gun had a maximum range of 16,916 meters with a rate of fire of one round every two minutes. The engine was mounted in the front and drove through a front-drive sprocket. The driver's cupola is visible on the front left of the turret, and spare track blocks were stored on the turret front. The M55 saw action during the Vietnam War, and was then withdrawn from US military service. Created in 1957, this field manual reveals a great deal about the M53's design and capabilities. Intended as a commander's manual for training crew members, it details many methods of attaining effecient teamwork while operating the gun. Drills are described in detail, with the ultimate goal being the successful operation of the M53 and M55 on the battlefield. Originally labeled restricted, this manual was declassified long ago and is here reprinted in book form. Care has been taken to preserve the integrity of the text."