The important family of Douglas observation aircraft sprang from two XO-2 prototypes, the first of which was powered by the 420 hp (313 kW) Liberty V-1650-1 V-engine and test-flown in the autumn of 1924. The second XO-2 was powered by the 510 hp (380 kW) Packard 1A-1500 Vee engine, which proved unreliable. The US Army ordered 45 O-2 production aircraft in 1925, these retaining the XO-2's welded steel tube fuselage, wooden wings and overall fabric covering but at the same time introducing aluminium panels on the forward fuselage. The XO-2 had been flown with short and long-span wings, the latter giving improved handling and therefore being specified for the production aircraft. The fixed tailskid landing gear included a main unit of the divided type, the horizontal tail surface was strut braced, and the engine was cooled by a tunnel radiator.
The O-2 proved to be a conventional but very reliable biplane which soon attracted orders for 25 more aircraft: 18 O-2A machines equipped for night flying and six O-2B dual-control command aircraft for the US Army, plus one civil O-2BS modified specially for James McKee, who made a remarkable solo transCanada flight in September 1926. In 1927 the O-2BS was adapted as a threeseater with a radial engine.
The O-2Hs were an entirely new design but continued the same basic model number. Major differences were heavily staggered wings, a more compact engine installation, and clean landing gear secured to the fuselage.
Up to 2011 there were no O-2's known to exist. However in 2011 the wreckage of O-2H 29-163 that crashed out of Kelly Field Texas on March 16, 1933 has been positively identified. The rear and central/forward portion of the fuselage behind the firewall, wing attachments and landing gear parts, tailplane and many engine parts and eight of the twelve pistons are now recovered. Research is continuing on this aircraft. It is known it was flown by Aviation Cadet Charles D. Rogers on a night recon advanced training mission. Apparently flying low, the aircraft hit a hill and burned after the crash leaving only the found wreckage today. Weather was not considered a contributing factor. Cadet Rogers was instantly killed in the crash by the impact. His body was recovered but the wreckage was abandoned due to the airframe and engine both being a write-off.
The only similar aircraft known to exist are a restored Douglas M-2 mailplane and a follow-on derivative of the O-25 variant, an O-38.
These differed from the O-2 in having frontal radiators for their Liberty engines and modified oleo-strut landing gear. The USAAC took delivery of 18 aircraft, while the remaining 27 went to reserve National Guard units - 45 built and one later conversion from O-9.
Unarmed staff transport versions of the O-2C - two built.
A one-off aircraft which replaced the wire link between upper and lower wing ailerons of production aircraft by rigid struts.
The fuselage was redesigned and a new tailplane was fitted, with staggered wings of unequal span. The O-2H incorporated the rigid-strut aileron interconnections of the O-2E. An improved split-axle landing gear was standard. The USAAC received 101 O-2Hs between 1928 and 1930, and the National Guard a further 40 - 141 built.
Unarmed dual control version of the O-2H for service as USAAC staff transports - three built.
A slightly modified version of the O-2J for US Army staff transport and liaison duties. 30 built for the USAAC and 20 for the National Guard - 50 built.
The 46th aircraft of the original O-2 contract was completed as an attack machine with the powerplant of one 420 hp (313 kW) V-1410 Liberty inverted-Vee engine, and with a total of eight machine-guns (two in the engine cowling, two each in the upper and lower wings, and two on a ring-mounting operated by the observer). It was remarkably well armed for its day, and competed against the Curtiss A-3 in 1926 but was not selected for production.
First production model, 146 built. 58 later converted to BT-2BI instrument trainers. Two converted to BT-2BR and 15 to BT-2BG radio-controlled aerial target drones.
Second production model, 20 built. 13 converted to BT-2CI instrument trainers. Seven became BT-2CR drone controllers.
Seventeen BT-2BRs and BT-2BGs converted in 1940 as radio-controlled aerial target drones. These had tricycle gear (a steerable nosewheel was added) with main gear moved aft, faired-over rear cockpit, and single controls, allowing the aircraft to be test-flown.