Zone libre
Rosenthal's musical career was interrupted by World War II when, as a corporal in the 300th infantry regiment stationed in 1939 in Alsace near the Rhine, he was taken prisoner by the Germans in May 1940. Still musically active even as a POW, he not only organized concerts in the camp he was interned in but even composed an operetta based on a play by Georges Courteline. Included in a POW exchange, he was sent back to the occupied zone, arrived back in Paris in March 1941 and escaped to Marseille in the Zone libre (free zone) with the help of Roland-Manuel. But he was arrested in Besançon in September 1941 while trying to see his son and sentenced to six months forced labor. With the assistance of a German officer, however, he got the necessary papers to escape back to Marseille. Later in 1942, he returned to Paris and courageously joined the Resistance, working with eminent musical colleagues Désormière, Durey, Delvincourt, Charles Munch and others.