Henry Post Army Airfield (IATA: FSI, ICAO: KFSI, FAA LID: FSI) is a military use airport located at Fort Sill in Comanche County, Oklahoma, United States. This military airport is owned by United States Army. Established as Post Field in 1917, it was one of thirty-two Air Service training camps established after the United States entry into World War I in April 1917.