III, 76 PzIV, 77 Pz35(t), 13 PzBef III, 7 PzBef 38(t), 34 other PzBef and some Pz38(t)) were lost during the campaign, approximately 341 of which were never to return to service. This represented about a third of Germany's armor deployed for the Polish campaign. During the campaign no less than a half of Germany's tanks were unavailable due to maintenance issues or enemy action, and of all tanks, the Panzer I proved the most vulnerable to Polish anti-tank weapons. Furthermore, it was found that handling of armored forces during the campaign left much to be desired. During the beginning of Guderian's attack in northern Poland, his corps was held back to coordinate with infantry for quite a while, preventing a faster advance. It was only after Army Group South had its attention taken from Warsaw at the Battle of Bzura that Guderian's armor was fully unleashed. There were still lingering tendencies to reserve Germany's armor, even if in independent divisions, to cover an infantry advance or the flanks of advancing infantry armies. Although tank production was increased to 125 tanks per month after the Polish Campaign, losses forced the Germans to draw further strength from Czech tank designs, and light tanks continued to form the majority of Germany's armored strength. The occupation of Czechoslovakia in March 1939 had provided the German military with large amounts of high quality weapons at no cost, from the arsenal of the Czech military. There was enough equipment for about 40 army divisions. The Germans integrated the Czech industry, mainly the Skoda factories, becoming part of the German military production machine and continued to produce tanks and other weapons for Germany. So when Germany invaded France, three full German Panzer divisions were equipped with Czech tanks. One division was equipped with the Czech type 35 light tank (10 tons) known as Panzer 35(t), and two divisions were equipped with the type 38 light tank (10 tons) renamed Panzer 38(t). The Panzer 35 had a crew of four and carried a Czech 37mm gun (with 72 rounds) and two machine guns, one coaxial and remained in front line service until 1942, when they were converted for other roles. The Panzer 38 had a crew of four and carried a Czech 37mm gun (with 90 rounds) and two machine guns, one coaxial and one in the front (with 2550 rounds). 1400 tanks were produced for the