War returned in September 1939 and Walter Kämpf was conscripted into the wartime army. Bizarrely, Nazi Germany was now unexpectedly on the same side as the Soviet Union which invaded Poland from the east sixteen days after the German invasion from the west (which according to mainstream anglophone historiography triggered the war). For many of those, such as Kämpf, who retained an active commitment to the illegal Communist Party, it was hardly possible to oppose unhesitatingly the alliances entered into by Stalin and the comrades in Moscow. Kämpf's attitude to the Stalin-Hitler alliance is unclear, but any unease would have been resolved when the Germans changed sides and, in June 1941, invaded the Soviet Union. A month later, in July 1941, Walter Kämpf switched to work as a paramedic, assigned to a military hospital for Luftwaffe casualties. His role was still essentially, a military one, however: by the time of his arrest he would have reached the rank of "Luftwaffenobergefreiter" ("loosely, "flight sergeant"").