^"Friedrichshafen FF.21". www.airwar.ru (in Russian). Retrieved 1 March 2019.
Bibliography
Herris, Jack (2016). Friedrichshafen Aircraft of WWI: A Centennial Perspective on Great War Airplanes. Great War Aviation Centennial Series. Vol. 21. Charleston, South Carolina: Aeronaut Books. ISBN978-1-935881-35-3.
Further reading
Kober, Theodor von; Borzutzki, Siegfried (1993). Flugzeugbau Friedrichshafen GmbH : Diplom-Ingenieur Theodor Kober (in German) (1. Aufl ed.). Burbach. pp. 98-99. ISBN978-3927513600.
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