The 27th Aero Squadron was a United States Army Air Service unit that fought on the Western Front during World War I. The squadron was assigned as a Day Pursuit (Fighter) Squadron as part of the 1st Pursuit Group, First United States Army. Its mission was to engage and clear enemy aircraft from the skies and provide escort to reconnaissance and bombardment squadrons over enemy territory. It also attacked enemy observation balloons, and perform close air support and tactical bombing attacks of enemy forces along the front lines.