Vahlen had studied under Frobenius and written his dissertation on additive number theory. He had been published in mathematical journals like "Crelle's Journal" and "Acta Mathematica". Vahlen's mathematical interests included partition theory, non-Euclidean geometry and differential equations. His published works on applied mathematics included papers on ballistics, aerodynamics, the magnetic compass and celestial mechanics. By 1911 Vahlen was teaching in Greifswald. Between 1914 and 1915 he served on the Western Front of World War I. He was wounded during his service on the Eastern Front (1916-1919) and left the army a decorated, high-ranking officer. He joined the Nazi Party after the failed Beer Hall Putsch and visited Hitler at Landsburg prison in 1924. He lost his teaching position after taking down the Weimar flag at the University of Greifswald. After living in Vienna for a time, Vahlen returned to Germany only after Hitler became Chancellor in 1933. Bernhard Rust had become the Reich education minister and supported Vahlen's return.