During the initial campaigns of World War II, Germany's light tanks, including the Panzer I, formed the bulk of its armoured strength. In March 1938, the German Army marched into Austria, experiencing a mechanical breakdown rate of up to thirty percent. However, the experience revealed to Guderian several faults within the German "Panzerkorps" and he subsequently improved logistical support. In October 1938, Germany occupied Czechoslovakia's Sudetenland, and the remainder of the country in March 1939. The capture of Czechoslovakia allowed several Czech tank designs, such as the Panzer 38(t), and their subsequent variants and production, to be incorporated into the German Army's strength. It also prepared German forces for the invasion of Poland.