 During the resistance he adopted the pseudonym Valrimont, among others.When arrested in Lyon on March 15, 1942, his knowledge of German as a native of Alsace allowed him to conceal his true identity from his interrogators, and he thus faced only minor charges.On May 24 he escaped from prison with several colleagues and resumed his activities, organising sabotage in factories and opposing the drafting of French labour for the German war effort.