The primary German assault gun was the "Sturmgeschütz III" (StuG III). At about the same time (March 1942) as the howitzer-like KwK 37 gun was dropped from the Panzer IV's use, its "Sturmkanone" equivalent in the StuG III up to that time, was likewise replaced with a longer-barreled, high-velocity dual-purpose 75mm gun that had also been derived from the successful PaK 40 anti-tank towed artillery piece. The Germans also built a number of other fully armoured turretless assault guns, including the StuG IV, StuIG 33B, "Brummbär" and "Sturmtiger". The latter two were very heavy vehicles, and were built only in small quantities.