World War II broke out in September, and Zapf's unit was to be taken into the Wehrmacht. However, because of his heart trouble, Zapf was not transferred to the Wehrmacht but was instead dismissed. On 1 April 1942, he was summoned again for the war effort. Zapf had been chosen for the Luftwaffe, but instead was sent to the artillery in Weimar. He did not perform well, confusing left and right during training and being too cautious and clumsy with his gun. His officers soon brought an unusually early end to his career in the artillery.