With the U.S. Army during World War II, he was a war correspondent starting in 1943 for the North American Newspaper Alliance and Fawcett Publications, publisher of "True". He followed Allied forces to Algeria as part of Operation Torch, and accompanied the Allied troops during their invasion of Sicily and their subsequent invasion of mainland Italy. Together with Fred Rosen, Stern entered Rome on June 3, 1944, one day before the American forces, under General Mark Wayne Clark, took control of the city from the retreating German Army.