The onset of World War II created a significant shortage of professional baseball players, as more than 500 men left MLB teams to serve in the military. Many of them played on service baseball teams that entertained military personnel in the US or in the Pacific. MLB teams of this time largely consisted of young men, older players, and those with a military classification of 4F, indicating mental, physical, or moral unsuitability for service. Men like Pete Gray, a one-armed outfielder, got the chance to advance to the major leagues. However, MLB rosters did not include any black players through the end of the war. Black players, many of whom served in the war, were still restricted to playing Negro league baseball.