Flügge also extended Niels Bohr’s and J. A. Wheeler’s theory of nuclear fission published in 1939. The papers by Flügge on the exploitation of nuclear energy were an impetus for action. For example, the Auergesellschaft had a substantial amount of “waste” uranium from which it had extracted radium. After reading Flügge’s paper in Die Naturwissenschaften on the technical use of nuclear energy from uranium, Nikolaus Riehl, the scientific director at Auergesellschaft, recognized a business opportunity for the company. In July 1939, he went to the "Heereswaffenamt" (HWA, Army Ordnance Office) to discuss the production of uranium. The HWA was interested. In 1940, on the initiative of Rudolf Tomaschek, despite Wilhelm Müller’s objection, Flügge lectured at the "Technische Hochschule München" on theoretical physics during the winter semester. From 1941, he was a lecturer at the "Friedrich-Wilhelms-Universität" (today, the Humboldt University of Berlin). In 1944, Flügge was an ordinarius professor at the University of Königsberg. From 1945 to 1947, he took a position at his "alma mater", the University of Göttingen. From 1947 to 1949, he had a position at the "Philipps-Universität Marburg". From 1949 to 1950, he was a visiting professor at the University of Wisconsin–Madison and in 1953 at the Carnegie Institute of Technology. Later, he was at the "Albert-Ludwigs-Universität Freiburg". From 1956 to 1984, Flügge was editor of the 54-volume, prestigious "Handbuch der Physik" ("Encyclopedia of Physics") published by Springer-Verlag. The following reports were published in "Kernphysikalische Forschungsberichte" ("Research Reports in Nuclear Physics"), an internal publication of the German "Uranverein". The reports were classified Top Secret, they had very limited distribution, and the authors were not allowed to keep copies. The reports were confiscated under the Allied Operation Alsos and sent to the United States Atomic Energy Commission for evaluation. In 1971, the reports were declassified and returned to Germany.