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The AGO S.I was a German prototype ground-attack aircraft built in October 1918 but possibly never flown before the end of World War I. It was a single-seat biplane armed with a downwards-firing 20 mm cannon.
Herris, Jack (2012). German Armored Warplanes of WWI: A Centennial Perspective of Great War Airplanes. Great War Aviation Centennial Series. Vol. 4. Charleston, South Carolina: Aeronaut Books. ISBN978-1-935881-11-7.
Taylor, Michael J. H. (1989). Jane's Encyclopedia of Aviation. London: Studio Editions. p. 40.