 Franck enlisted in the German Army soon after the outbreak of the First World War in August 1914 . In December he was sent to the Picardy sector of the Western Front . He became a deputy officer ( <unk> ) , and then a lieutenant ( <unk> ) in 1915 . He was awarded the Iron Cross , Second Class , on 30 March 1915 , and the city of Hamburg awarded him the Hanseatic Cross on 11 January 1916 . While in hospital with pleurisy , he co @-@ wrote yet another scientific paper with Hertz , and he was appointed an assistant professor in his absence by Frederick William University on 19 September 1916 . Sent to the Russian front , he came down with dysentery . He returned to Berlin , where he joined Hertz , Westphal , Hans Geiger , Otto Hahn and others at Fritz Haber 's Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry , working on the development of gas masks . He was awarded the Iron Cross , First Class , on 23 February 1918 . He was discharged from the Army on 25 November 1918 , soon after the war ended . 
