The Panzer III was used in the campaigns against Poland, France, the Soviet Union and in North Africa. A handful were still in use in Normandy and at Arnhem in 1944.In the Polish and French campaigns, the Panzer III formed a small part of the German armored forces. Only a few hundred Ausf. A through F were available in these campaigns, most armed with the 37-millimetre (1.46 in) gun. They were the best medium tank available to the Germans and outclassed most of their opponents such as the Polish 7TP, French R-35 and H-35 light tanks.

The Panzer III was well designed in that it had a three-man turret crew (gunner, loader and commander), leaving the commander free to concentrate on commanding the tank and maintaining situational awareness. Although other medium tanks of the time also had this feature, most tanks of the late 1930s had fewer than three men in the turret crew, potentially providing the Panzer III with a "fightability" advantage over otherwise similar tanks, such as the French Somua S-35, which only had a one man turret crew.The Panzer III chassis was the basis for the Sturmgeschütz III assault gun, one of the most successful self-propelled guns of the war.
                                                                                                                                           -- Wikipedia