The Battle of France, the German invasion of France and the Low Countries, began on 10 May 1940. On 18 May 1940, he engaged in aerial combat with eight French Curtiss P-36 Hawk fighter aircraft and was shot down west of Rethel. His victor may have been "sous lieutenant" Camille Plubeau. Wilcke bailed out and was taken prisoner of war. Following the armistice with France, he and Mölders, who had also been a prisoner of war, returned to the unit on 30 June 1940. Wilcke was promoted to "Hauptmann" the next day and again took command of 7. "Staffel". On 11 July 1940, he was awarded the Iron Cross 1st Class ().