[5] In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting they had detected the element barium after bombarding uranium with neutrons;[6] simultaneously, they communicated these results to Lise Meitner, who had in July of that year fled to The Netherlands and then went to Sweden.

[9] Flügge and Gottfried von Droste, an assistant to Meitner, independently also predicted a large energy release from nuclear fission.

Some with whom he collaborated were Carl Friedrich von Weizsäcker and Fritz Houtermans on the theoretical basis of the Uranmaschine (literally uranium machine, i.e., nuclear reactor).

After reading Flügge’s June 1939 paper[12] 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.

[14][15] 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.

[17] From 1956 to 1984, Flügge was editor of the 54-volume, prestigious Handbuch der Physik [de] (Encyclopedia of Physics) published by Springer-Verlag.

The reports were confiscated under the Allied Operation Alsos and sent to the United States Atomic Energy Commission for evaluation.