The Sturmpanzer IV Brummbär (SdKfz 166) 150mm assault gun was introduced to provide fire support against heavily fortified targets and stronpoints. This vehicle was based on the Panzer IV chassis, was heavily armored, and was armed with a short-barreled low-velocity 150mm gun. While the initial production vehicles lacked any secondary armament, later Sturmpanzer IV's were fitted with a ball-mounted 7.92mm machine gun firing through the hull glacis, plus another machine gun on the hull roof for air defense. All production vehicles also had a pistol port on each side of the superstructure.