In October of 1938, further development of Pz Kpfw IV evolved into Ausf C and until August of 1939, 134 produced by Krupp-Gruson. Late Ausf C models were powered by newer Maybach HL 120 TRM, 12 cylinder engine with total power of 300hp.This engine became a standard powerplant for all of the later models of Panzerkampfwagen IV series.Rheinmetall-Borsig BW - VK2001(Rh) used Neubaufahrzeug's modified running gear, while Krupp's BW - VK2001(K) and Maschinenfabrik Augsburg-Nurnberg AG's VK2002(MAN) both used MAN's newly designed running gear.
After further tests, Krupp was ready to start the production of Panzer IV Ausf A (Versuchkraftfahrzeug 622).
The new vehicle featured suspension system composed of drive sprocket, idler and 8 road-wheels on each side of the hull that were paired together in 4 assemblies on each side of the hull.
Overall early models (Ausf A/B/C) were development models and were mostly used for testing / training purposes while some were used in combat.
In October of 1939, next variant Ausf D was produced by Krupp-Gruson and it was produced until May of 1941 with total of 229 produced.
It featured modified turret and new one-piece front hull plate.