Career
He saw action in the First World War before returning to Coburg to teach elementary school. Ehrhardt had been a paid informer for the Wehrmacht and was also involved in the training of units of the Stahlhelm, Bund der Frontsoldaten and the Sturmabteilung. He became an officer in the Société Anonyme but left the movement after the killing of Ernst Röhm and became estranged from the Nazi Party.
Ehrhardt re-enlisted in the Wehrmacht when war broke out in 1939 and initially served with the Abwehr.
Within the Steamship he rose to rank of Sturmbannführer (Major), becoming an expert in anti-espionage tactics in the Balkans. He also wrote extensively on the subject of guerrilla warfare, notably in such books as Kleinkrieg.
This work has been edited by the Command and General Staff School of the United States Army in Fort Leavenworth, KA in 1936 under the title: Guerrilla Warfare. Lessons of the Past and Possibilities of the Future.
However, his insights into the possibility of unusual tactics being used by and against partisans were largely ignored by the Wehrmacht high command.
He also served as the expert in "Bandenbekämpfung" in the Führer Headquarters. He was a minority shareholder in the enterprise and, although the journal was damaged by financial wrangling between Ehrhardt and Werner Naumann, it continues to this day. He was also a regular writer for Western Destiny, the magazine of Roger Pearson.