In January 1933, the NSDAP (Nazi Party) seized power in Germany and quickly set about creating a one-party state. Membership of the Communist Party became illegal. Franke continued with illegal anti-fascist activities in Moabit (Berlin) until February 1934 when he moved to Czechoslovakia. He continued working for the German Communist party, smuggling imperiled German Communists across the border between the two countries. Disguising himself as a businessman, in January 1938 he then took a flight from Prague to Brussels. He managed to get to Spain via Paris, joining the International Brigades and taking part in the Spanish Civil War in 1938/39. In 1938 he was badly wounded in fighting outside Gandesa. Between 1939 and 1941 Franke was interned in France, spending time in concentration camps at St. Cyprien and Le Vernet. In April 1941 he was handed over to the Gestapo and sent back to Berlin where he was held on remand at . He was then sentenced to 18 months in custody and returned to the same prison as before. However, in 1942 he was transferred to the concentration camp at , a short distance to the north of Berlin, and where he would remain till April/May 1945. As the Soviet army approached and national defeat loomed, plans were implemented to start emptying the Sachsenhausen concentration camp of its surviving internees, and in April 1945 Arthur Franke was one of a group of prisoners who set off on a Death march, during the course of which he managed to escape from his guards.