The concept was to mount a high-calibre, high-explosive weapon on a fully enclosed superstructure, the gun chosen was the potent 150mm SIG-33 heavy infantry gun on a Pz Kpfw III chassis, the resultant armoured fighting vehicle first put the crew of the 150mm heavy infantry gun under armoured protection and provided a nearly optimal solution for the situation. The uniqueness and strength of the “Heavy escort artillery†as an assault vehicle in armoured units was a successful solution.