As the son of a Jewish anti-Nazi activist, Oscar Cahén experienced Nazi oppression first hand. After fleeing Prague and arriving in England in 1939, however, he was soon detained because of his German citizenship. He was then sent to Canada where he was interned at Sherbrooke, Quebec as a prisoner of war. His talent led to his release. Cahén then found work designing war graphics with the National Film Board's designer Harry Mayerovitch, and with the art studio Rapid, Grip and Batten.