The M55 was an American fully enclosed and armored self-propelled artillery based on the M53 155 mm 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 (10.51 miles) with a rate of fire of one round every two minutes. The M55 armor was light, 25 mm maximum, but sufficient to protect the crew from indirect artillery hits or small arms fire.