it is safe to assume neither adaptation was successful beyond the drawing board. Second World War 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. On 1 September 1939, Germany invaded Poland using seventy-two divisions (including 16 reserve infantry divisions in OKH reserves), including seven panzer divisions (1., 2., 3., 4., 5., 10., "Kempf") and four light divisions (1., 2., 3., 4.). Three days later, France and Britain declared war on Germany. The seven panzer and four light divisions were arrayed in five armies, forming two army groups. The battalion strength of the 1 Panzer Division included no less than fourteen Panzer I's, while the other six divisions included thirty-four. A total of about 2,700 tanks were available for the invasion of Poland, but only 310 of the heavier Panzer III and IV tanks were available. The Germans held some 1,400 of Panzer Is at the ready during the invasion. Furthermore, 350 tanks were of Czech design—the rest were either Panzer I's or Panzer IIs. The invasion was swift and the last Polish pockets of resistance surrendered on 6 October. The entire campaign lasted five weeks with Poland attacked from the East by the USSR from 17 September. and the success of Germany's tanks in the campaign was summed up in response to Hitler on 5 September: when asked if it had been the dive bombers who destroyed a Polish artillery regiment, Guderian replied, "No, our panzers!" The Poles suffered almost 190,000 casualties (including around 66,300 killed) in the campaign, the Germans around 55,000 (including around 35,000 wounded). However, some 832 tanks (including 320 PzI, 259 PzII, 40 Pz