Decker was appointed commander of the XXXIX Panzer Corps that was attached to the 3rd Panzer Army and promoted to General der Panzertruppe on 1 January 1945. After his unit was relocated to the Western Front, his corps fought the Americans at Uelzen and in the Alsace. Here the 5th Panzer Army was subordinated to Army Group B. Decker committed suicide on 21 April 1945 after the defeat and encirclement of the Army Group in the Ruhr Pocket in April.
