After 1939, Müller and Karl-Heinz Höcker collaborated with Carl Friedrich von Weizsäcker at the Kaiser-Wilhelm Institut für Physik, in Berlin-Dahlem, on the theory behind the Uranmaschine. Many at the KWIP and those working on the Uranmaschine had the classification of unabkömmlich and were exempt from being drafted into armed service. Both Müller and his colleague Höcker had the classification uk, but their fates were quite different. As the war raged on, the demand for men to provide armed service resulted in Höcker and Müller being drafted in late 1940 or early 1941. Not even Kurt Diebner, managing director of the KWIP, could stop the call-up. Höcker was returned to the KWIP in 1942 due to poor health; Müller had died at the Russian front. It was not until 1944 that Werner Osenberg, head of the planningboard at the Reichsforschungsrat, was able to initiate calling back 5000 engineers and scientists from the front to work on research categorized as kriegsentscheidend. By the end of the war, the number recalled had reached 15,000. Many of the scientists called for military service were at institutes under the Kaiser-Wilhelm Gesellschaft.
Internal reports
The following reports were published in Kernphysikalische Forschungsberichte, 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. The reports are available at the Karlsruhe Nuclear Research Center and the American Institute of Physics.
P. O. Müller Der Wirkungsquerschnitt der Uranspaltung G-7
Paul MüllerDie Energiegewinnung aus dem Uranspaltungsprozess durch schnelle Neutronen G-49
Paul Müller Eine Bedingung für die Verwendbarkeit von Uran als Sprengstoff G-50
Paul Müller Die Neutronenabsorption in Kugelschalen aus Uran G-51
Paul Müller Über die Temperaturabhängigkeit der Uranmaschine G-52
Paul Müller Berechnung der Energieerzeugung in der Uranmaschine. III Schweres Wasser G-53
Carl-Friedrich von Weizsäcker, Paul Müller, and Karl-Heinz Höcker Berechnung der Energieerzeugung in der Uranmaschine G-60
