Lieutenant William Thomas Barnes was an English flying ace of World War I.
He served as an observer/gunner in Bristol F.2 Fighters, gaining, in conjunction with his pilots, nine confirmed aerial victories (6 destroyed, 3 'out of control') over German Fokker D.VII fighter planes.
Postwar he served in the Royal Irish Constabulary and was killed in the Kilmichael ambush of 28 November 1920.