German tank destroyers based on the Panzer III and later German tanks were unique in that they had more armor than their tank counterparts. One of the more successful German tank destroyers was actually designed as a self-propelled artillery gun, the "Sturmgeschütz III". Based on the Panzer III tank chassis, the "Sturmgeschütz III" was originally fitted with a low-velocity gun, and was assigned to the artillery arm for infantry fire support. Later, after encountering Soviet tanks, it was refitted with a comparatively short-barreled high-velocity anti-tank gun, usually with a muzzle brake, enabling it to function as a tank destroyer. The "Sturmgeschütz III" from its 1938 origin used a new casemate-style superstructure with an integrated design, similar to the later "Jagdpanzer" vehicle designs' superstructure, to completely enclose the crew. It was employed in infantry support and offensive armored operations as well as in the defensive anti-tank role. The StuG III assault gun was Germany's most-produced fully tracked armoured fighting vehicle during World War II, and second-most produced German armored combat vehicle of any type after the Sd.Kfz. 251 half-track.