Ranke was a member of the Weimar Republic paramilitary Stahlhelm organization, which was dissolved and integrated into the Sturmabteilung (SA) from 1934 to 1935, and was a member of the National Socialist Teachers League. In 1935, Ranke joined the Aviation Medical Research Institute of the Military Medical Academy in Berlin, where Hubertus Strughold worked. Ranke was appointed in 1936 to außerplanmäßiger (extraordinary) professor at the University of Berlin.