Regarding our volumes 19, 22, 26 and 43 there is one important vehicle missing sd.Kfz. 166 15cm SIG33 on Panzer IV "Brummbär." During the defensive battles on the eastern front, the need for a successor vehicle on a Kampfwagen IV chassis became noticeable, because the 2 small series of such vehicles on a Panzer Iii chassis were almost used up in the summer of 1943 and the following months. Therefore, in the second half of 1944, corresponding development orders were placed with German industry, which quickly ended in proposals for the Brummbär.