Scott Air Force Base is a United States Air Force base in St. Clair County, Illinois, near Belleville and O'Fallon, 17 miles (27 km) east-southeast of downtown St. Louis. Originally Scott Field, it was one of 32 Air Service training camps established after the United States entered World War I in April 1917. The present base serves as the headquarters of Air Mobility Command (AMC) and its showcase wing, and it is also the headquarters of the U.S. Transportation Command, a Unified Combatant Command that coordinates transportation across all the services.