The Invasion of Poland had shown that the towed sIG 33 guns assigned to the infantry gun companies of the motorized infantry regiments had difficulties keeping up with the tanks during combat. The easiest solution was to modify a spare tank chassis to carry it into battle. A SIG 33 was mounted on the chassis of the Panzer I Ausf. B, complete with carriage and wheels, in place of the turret and superstructure.
