During the initial campaigns of the Second World War, Germany's light tanks, including the Panzer I, formed the bulk of its armored strength. In March 1938, the German Army annexed 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. Germany also had some other tanks that were to prove useful in the early part of the war. In October 1938, Germany annexed the Sudetenland in Czechoslovakia, and parts of the remainder of the country in March 1939 to be limited to Bohemia and Moravia. The conquest 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.