During the inter-war years, Schlemm served in a variety of staff, training and regimental posts until, in October 1937, he was attached to the Reich Air Ministry.

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.

On 6 October 1943, part of Schlemm's corps collapsed under a major Soviet attack, resulting in a 10-mile gap in the German lines and the abandonment of Nevel.

They were initially dispatched from Rome to bolster the Winter Line along the Garigliano River, but soon Schlemm's corps were urgently transferred to oppose the Allied beachhead at Anzio (Operation Shingle).

Schlemm led the German troops for three days until command formally passed to Generaloberst Eberhard von Mackensen, Commander-in-Chief of the 14th Army.

After the Winter Line was breached at Cassino and the Anzio bridgehead breakout, Schlemm's Corps joined the German withdrawal through central Italy.