From 1889 to 1895, Oehler was a student at Pforta. He then joined the Prussian Army, although he also showed considerable interest in literature and especially music. He would often express to his cousin Elisabeth Förster-Nietzsche a wish to work at her "Nietzsche-Archiv" someday. Nevertheless, his main interest was his career in the army, whose values he deeply admired. He was made Oberleutnant in 1908, Hauptmann in 1912, and was allowed to call himself Major when he left the army in 1919. For a long time, he was stationed in Deutsch Eylau, today Iława.