While awaiting his commission he was appointed as a Fähnrich (junior non-commissioned officer) in the 66th Field Artillery Regiment of the 39th Division.

The regiment was deployed to Kolmar in Alsace-Lorraine and at the outbreak of World War I they saw action along the eastern border of Germany known as the Battle of the Frontiers.

In April 1915, Bader was promoted to Hauptmann (captain) and was appointed as the adjutant to the commander of the 39th Field Artillery Brigade.

Following the successful end of the Polish campaign, Bader's division was transferred to the west to prepare for the invasion of France.

In May and June 1940, Army Group A thrust through the Ardennes, across the Meuse and towards the Channel Ports of Dunkirk and Calais then south to outflank the Maginot Line.

Bader ordered on January 3 1942 that admitting Jews into their homes and hiding their things and value papers is punishable by death.

[6] On 26 August 1943 he was transferred to command the newly created XXI Mountain Corps in Albania, however he was only in this position for a few months before he was placed on the Führerreserve list in October 1943 then retired on 31 March 1944, having served in the German Army for 41 years.