An assault gun is a gun or howitzer mounted on a motor vehicle or armoured chassis, designed for use in the direct fire role in support of infantry when attacking other infantry or fortified positions. The term is a literal translation of the German word Sturmgeschütz. Nazi Germany introduced the first purpose-built assault gun, the StuG III, in 1940, thus establishing this category of armoured vehicles.
Historically, the custom-built fully armoured assault guns usually mounted the gun or howitzer in a fully enclosed casemate on a tank chassis. The use of a casemate instead of a turret limited these weapons' field of fire, but allowed a larger gun to be fitted relative to the chassis, more armour to be fitted for the same weight, and provided a cheaper construction. In most cases, these turretless vehicles also presented a lower profile as a target for the enemy.
The assault gun looks and works in the same way as the similar tank destroyer, the only difference in most cases being the gun. Assault guns generally used larger calibre, lower velocity guns, with their primary ammunition being that of high-explosive shells; these were meant for taking out soft targets as outlined in its infantry support role. This was contrasted with the tank destroyer, which utilized higher velocity, and therefore smaller calibre guns, firing armour-piercing shells as their primary ammunition. Therefore, these vehicles often sacrificed being able to fire a good high-explosive shell in exchange for maximal armour penetration characteristics. Towards the beginning of the war, a single vehicle could generally be used in both roles, but that changed as the classes became increasingly specialized as the war progressed....LESS