He was a dental assistant before World War I, and earned a private pilot's license by Summer 1914.

He then transferred to the air service as a dental assistant before being accepted for military pilot training.

Bäumer joined Jagdstaffel 5 on 30 June 1917, scoring three victories as a balloon buster in mid-July before going to the elite Jasta Boelcke.

He was one of the few pilots in World War I whose lives were saved by parachute deployment, when he was shot down in flames in September.

He received the Pour le Mérite shortly before the Armistice and was finally credited with 43 victories, ranking ninth among German aces.