Early in development the Heer settled on the concept of the tank having a commander who was in radio communication with his superiors. Thus the basic design of the main battle tanks called for a larger turret that would house the tank commander, gunner and loader, while a driver and a machine gunner were down in the hull. Guderian insisted on the tank commander being in radio communication with both his platoon and with the members of his own tank crew. Though the Panzer III was conceived as the main battle tank of the Wehrmacht, the Wehrmacht did not anticipate being at war with Europe's major powers in 1939, and few were available at the start of the war. Excluding Czech-built tanks, on 1 September 1939 the invasion of Poland was undertaken with the German armoured force of 3,195 tanks evenly split between the Pz I training tank and the Pz II light tank; of the main battle tanks, only 98 Pz IIIs were in service during the invasion of Poland, along with 211 Pz IVs, with 215 tanks of various models also available as command tanks after being modified by having their main armament removed and extra communications equipment installed.