curtiss had developed the eagle in preparation for an anticipated post-war boom in civil aviation. in fact, this boom was far smaller than curtiss had been hoping for, and practically all of the demand for passenger aircraft was met by the conversion of war-surplus military aircraft that could be purchased extremely cheaply. as such, only around 20 machines were built. the original trimotor eagle design was followed by a single example of the eagle ii, with twin engines, and by three eagle iiis with only one engine. these latter aircraft were purchased by the united states army air service, which used them as staff transports and converted one example into an air ambulance.