Early aircraft of Ad Astra Aero. In the background is CH-2, a LVG C.V. The Kondor E.3 fighter was a design of the Kondor Flugzeugwerke in Essen. It received the German army designation D.I but only a few examples were delivered before the Armistice. The E.3a was apparently a single aircraft powered by a Goebel Goe III engine. Mattenhof airfield was in the Schwamendingen suburb of Zürich. Photo by: Walter Mittelholzer / ETH-Bibliothek Zürich