From the release:
Known officially as the Sd.Kfz 166 or Sturmpanzer 43, this heavy assault gun is better known by the nickname Brummbär (German for Grizzly Bear), supposedly given to it by Allied Intelligence.
Based on a modified Panzer IV chassis the Brummbär was armed with a 150mm StuH 43/1 L/12 gun. Deveeloped for close range fire support, especially in regards to supporting units street-fighting. It was very effective against dug-in infantry positions, buildings and almost any kind of stronghold. They were also used as support vehicles for panzergrenadier and infantry units.