The Douglas O-2 observation biplane, with its longer wings, had lower landing speeds, flew higher and was 22 mph faster than its competitors. The O-2, produced for the U.S. Army Air Service, was the first of a series that remained in production for nine years.

Douglas designed its first experimental observation aircraft, the XO-2, in 1923 and delivered 45 of the first production version, the O-2. An O-2BS, made for pilot James McKee, made the first single-aircraft, single-pilot flight across Canada. Because of the many Canadian rivers and lakes, twin floats were installed on the landplane. During the 1934 airmail emergency, Douglas biplanes flew the U.S. airmail routes for 78 days. Between 1923 and 1936, the company sold 879 in the series, one as a civil aircraft, 108 to foreign air forces and 770 to the U.S. military services.