The U.S. armed forces expanded dramatically during World War II. The draft, reinstated in 1940, inducted thousands into service, while thousands more enlisted voluntarily. On July 28, 1942, President Franklin D. Roosevelt announced that four million Americans were serving in the military.

Throughout the war, the military remained segregated by race as well as gender. African American and Japanese American soldiers served in separate regiments, while women joined special units such as the Women's Army Auxiliary Corps (WAAC) and the navy's Women Accepted for Volunteer Emergency Service (WAVES), both created in 1942.