The prototype TP-1 was built as the XTP-1 and tested at McCook Field in 1923. A biplane, the upper wing had a smaller span and narrower chord than the lower wing. The XTP-1 was armed with five .30 in (7.62 mm) machine guns and fitted with a 423 hp (315 kW) Liberty 12 engine. A second prototype was completed as an observation/reconnaissance aircraft with the designation XCO-5.
The XCO5 needed a high-lift wing suitable for high-altitude work. New wings were prepared. The aerofoil was Joukowsky StAe-27A, a heavily cambered wingshape with a thick leading edge. The upper and lower wings had a pronounced stagger, with a total wing area of 600 ft2. As well as lining and insulating the cockpit, heat was taken from the engine exhaust. A cover over the top of the cockpit kept the heat in; a clear panel in the cover allowed the pilot to see his instruments.
On October 10, 1928, Bill Streett and Albert William Stevens achieved an unofficial altitude record in the XCO-5 for aircraft carrying more than one person: 37,854 ft (11,538 m); less than 1,000 ft (300 m) short of the official single-person altitude record. At that height they measured a temperature of −78 °F (−61 °C), cold enough to freeze the aircraft controls. With frozen controls, Streett was unable to reduce altitude or to turn off the engine until some 20 minutes later when it ran out of fuel, after which he piloted the fragile experimental biplane down in a gentle glide and made a deadstick landing.