04/30/2007. Remarks by Jack Mckillop: "This was a one of a kind aircraft. The aircraft was tested at Wright Field, Dayton, Ohio, in June 1929 as P-559 and then purchased by the USAAC and the assigned Army designation and s/n were printed in large on the aircraft fuselage, as seen in the 3-view.

There were numerous cooling problems with the Curtiss Chieftain H-1640-1 12-cylinder, two row, radial, air-cooled engine and in September 1930, it was re-equipped with a Pratt & Whitney Wasp SR-1340C nine-cylinder, single row, radial, air-cooled engine and redesignated XP-13A. With the new engine, the Viper was 15 mph (24 kmh) faster than the original aircraft however, the aircraft crashed and was destroyed during an inflight fire and no others were ever purchased."