The self-propelled gun is essentially a 100-mm to 200-mm artillery piece (either field artillery, antitank gun, or antiaircraft gun) mounted in a turret on a medium or light tracked or wheeled vehicle that is armored to varying degrees. During World War II it was a useful antitank weapon, though a highly vulnerable one. After the war, the general trend among the remaining self-propelled guns was either toward lightly but completely armored models with guns mounted in turrets capable of all-around traverse, like most tanks, or toward partially armored models that were essentially tracked chassis with guns mounted on top. 