When the United States entered World War II, many Hollywood actors put their careers on hold to enlist in the armed forces and serve their country. But did you know that some male stars actually served in World War I before they become famous? Here are 10 of them. 1. Humphrey Bogart Bogart joined the U.S. Navy in May 1918. After four months of boot camp at the Pelham Bay Naval Training Station in New York, he was assigned as a helmsman to the transport ship SS Leviathan . Just as the crew was about to be shipped off to Europe, Germany surrendered and the war came to an end. However, he still sailed with the Leviathan from Hoboken, New Jersey to Liverpool, England. In the six months that followed the armistice, the ship was tasked with ferrying U.S. servicemen back from France and England. Reportedly, it was during this time that Bogart got the scar on his lip, which gave him his iconic lisp. He was discharged in June 1919. LEFT: Humphrey Bogart in his Navy uniform. He was a Seaman