It a Panzerkampfwagen (Pz.Kpfw.) III 'Zugführerwagen' (not PanzerKampfWagon ). I believe it's an Ausf. G, but I'm not completely sure. Christian
Sometime it's a real pain telling the exact model of the Panzer III and IV. Between tanks being rebuilt,upgraded or modified,a particular vehicle could have features unique to several different original models.
It is definatley not an E or F - the mantlet is wrong. It is either an Ausf. G, H or early J. Looking closer at the photograph, the radio operators machine gun mount is circular, which makes it an early Ausf. J. It isn't really that difficult to tell the difference if you get a high-quality photograph, but the above only have the most obvious details. The largest problem is telling a Pz.Kpfw. III Ausf. E from a Pz.Kpfw. III Ausf. F, because there was no real difference on the exterior. 'Zugführerwagen' was simply the code name for the Pz.Kpfw. III, just like Begleitswagen was the code name for the Pz.Kpfw. IV.
It is Panzerkampfwagen, yes - but not PanzerKampfWagon, as first written. Panzerkampfwagen was the generic word for all the regular tanks, just like Panzerjäger was the generic temr for all tank destroyers. Zugführerwagen was a code name, just like Landwirtschaftlicher Schlepper and Begleitswagen (whereas Panther and Tiger were the actual names, i.e. Panzerkampfwagen Panther or Panzerkampfwagen Tiger).