The 9th Aero Squadron was an Air Service, United States Army unit that fought on the Western Front during World War I. The squadron was assigned as an Army Observation Squadron, performing long-range, strategic night reconnaissance over the entire length of the United States First Army sector of the Western Front in France. It was the only night reconnaissance squadron of the Air Service stationed on the Western Front, and the squadron's emblem reflects an aircraft, flying at night with searchlights searching for it in a IX pattern.