 In October 1939, he became Chief of Staff of Luftgau [Air Zone] XI, under Generalleutnant Ludwig Wolff and in December 1940, Schlemm was appointed Chief of Staff of the XI Air Corps under General der Flieger Kurt Student.The Corps was the headquarters staff of Germany's parachute and air landing forces which, on 20 May 1941, the Germans used for Operation Merkur, the airborne invasion of Crete.At least 6,000 airborne troops were lost and the conquest of Crete effectively ended all plans for large-scale German airborne operations.