Douglas O-2 Series
What was wanted was a “good general utility ship” for the observation squadrons, and speed was not a major objective. The Liberty engine would be the power plant, although the airframe should be adaptable to more recent units like the Packard. As stated in the board’s report, the new type should have these characteristics:
“This airplane with Liberty engine proved to be without doubt the logical successor to the DH-4B. Its flying qualities appeared to be perfect, it was very maneuverable and controlled beautifully, it could not be made to spin from a stall and when attempts were made to force it in, it brought itself out immediately. It appeared to have no tricks, landed very easily and handled well on the ground. An outstanding characteristic was that each one who flew it felt perfectly at home in it from the first moment. For observation work, the plane was exceptionally good. The angles of vision and of flexible gun fire were excellent, the cockpit location nearly ideal and the arrangement very well worked out. The flexible guns were operated at high speed in dives and zooms with very pleasing results, the slipstream not affecting the accuracy of fire. The pilot’s angles of vision were very good for cross-country. In construction, the plane is a very simple and straightforward chrome molybdenum steel tube, wire-braced, fuselage, with single-bay wire-braced wings and wide tread axle less landing gear....”
Douglas had already won Army favor with their successful “World Cruiser” planes of 1924, and the new XO-2’s simple and neat proportions seemed to fit its role. Ordered in July 1924, the XO-2 was built by the Santa Monica firm in time for McCook Field tests to be completed December 11. A second airframe for static tests was supplied in May 1925. Fabric covered the usual steel tube fuselage and wood wing structure, and the new Clark Y airfoil was used.
The prototype had a Liberty with a smoothly shuttered chin radiator, but was also tested on January 12, 1925, with the 500-hp Packard lA-1500 and shorter wings. Top speed rose from 137 mph to 150 mph due to the reduced weight and size. That engine seemed unready for service adoption, however, so Liberty engines were specified for 75 production aircraft ordered February 16, 1925. It was the largest contract Douglas had received to date, and the largest Army two-seater contract since 1918.