The Panzer II, developed by Germany in the 1930s, was an improvement over the Panzer I, but it was still seen only as a stopgap measure in Germany’s goal of creating a powerful tank force. The Panzer II was widely used in early campaigns of WWII such as the invasion of Poland, the Low Countries and France, but by 1943 it had ceased production and the Panzer II chassis was being converted to other uses. At a maximum of only 16mm thick, the steel armor on early tanks proved inadequate. The main armament of most Panzer II variants was the 2cm Kw.K30 L/55 cannon and a coaxial MG34, although the main gun was mostly ineffective in the antitank role. A crew of three (commander, loader/radio operator and driver) operated the Panzer II. A 140hp six-cylinder Maybach HL 62 TRM engine powered the small tank to a maximum speed of 40km/h. The first series-production model was the Ausf.A, which appeared in July 1937. Sporting only superficial changes, the Ausf.B superseded it in December of the same year.