The 91st Aero Squadron was a Air Service, United States Army unit that fought on the Western Front during World War I. The 91st was one of the first five American flying squadrons to arrive in France, arriving at Chaumont Aerodrome on 15 November 1917. The current United States Air Force unit which holds its lineage and history is the 91st Network Warfare Squadron, assigned to the 67th Network Warfare Wing, Kelly Field Annex, Lackland Air Force Base, Texas.