Douglas O-2

Introduction and Development
Service Record
O-2 Variants
O-2 Derivatives

Introduction and Development

The Douglas O-2 was the first in a long series of observation biplanes that with nearly 900 produced were amongst the most important American military aircraft of their era.

Towards the end of the 1923 fiscal year the US War Department issued a series of contracts for prototypes of new observation aircraft to replace the First World War era DH-4Bs and DH-4Ms that were then in use with the Air Service. Douglas received two of those contracts, each for one aircraft - the first to be powered by the 420hp Liberty V-1650-1 engine and the second by a 510hp Packard 1A-1500 engine. Apart from the engines the aircraft were to be identical. Both aircraft were given the designation XO-2.

The Liberty powered XO-2 was the clear winner in its competitive trial, and on 25 February 1925 Douglas were awarded with a contract for seventy-five aircraft. This would eventually cover the O-2 (45 aircraft), O-2A (18 aircraft), O-2B (six), O-7 (three), O-8 (one), O-9 (one) and XA-2 (one) models.

The Packard powered XO-2 took part in its competitive trials at McCook Field early in 1925, but lost out to the Curtiss XO-1 Falcon. The Curtiss aircraft also entered production. Problems with the Packard engine meant that smaller numbers of the Curtiss machines were ordered, but the Falcon family did become more famous than the more numerous Douglas machines.

The XO-2 was a conventional biplane. It had a welded steel tube fuselage, wooden wings and was fabric covered. The wings were of equal span and were un-staggered and were connected by a mix of struts and bracing wires. Both prototypes had a tunnel radiator mounted under the engine, a divided main landing gear and rear tail skid. The horizontal tail plane was strut braced. Production aircraft had aluminium panels on the forward fuselage. Two sets of wings were tested on the Liberty powered aircraft, a 39ft 8in long span wing and a 36ft 3in short span wing. The long span wing was more successful, with better handling, lower landing speed and a higher ceiling, and was used on the production aircraft. 

Service Record

The O-2B was the first to enter service, arriving late in 1925. It was soon followed by the armed O-2 and O-2A, which were issued in the first part of 1926 to Observation Squadrons scattered across the United States. They were followed by the O-2C later in 1926 and the O-2H in 1928.

The O-2 took part in the air force manoeuvres of 1926, forming part of the attacking force. At this time it was serving with the 3rd Attack Group, after the failure of the purpose built GA-1 attack aircraft.

The O-2 also took part in the 1927 air exercise, an attack on a fictional enemy, once again as an attack aircraft with the 3rd Attack Group.

In 1928 the Air Corps carried out a series of aerial displays at Army service schools. Sixteen O-2s and nine A-3s made up the attack squadron for this display.

In 1930 one O-2K took part in an experimental deployment to Spokane, Washington, to test the ability of the Air Corps to operate in winter conditions. The O-2 was too slow to keep up with the fighters that made up the main force and had to abandon the trip.

In mid-1926 the Militia Bureau funded the purchase of fourteen O-2s for service with the National Guard. Later in the year eleven National Guard squadrons received two O-2Cs and another five received one each. This was the start of a long association between the O-2 family and the National Guard, which lasted into 1942. Fifty O-2Hs, twenty O-2Ks and a large number of O-38s went straight to the Guard, while the Air Corps passed a number of surplus aircraft to them.

O-2 Variants


The first forty-five aircraft were delivered as the O-2. This used the longer equal span un-staggered wings and the Liberty engine. It was similar to the first XO-2 but with a modified engine installation and tunnel radiator and aluminium panels on the forward fuselage. A jettisonable 30 US gallon fuel tank was mounted in the centre section of each lower wing. The O-2 had tripod main landing gear, each wheel being carried on an outer oleo leg and two struts that were hinged on the fuselage centre line. The O-2 was armed with one fixed forward firing 0.3in machine gun and one flexibly mounted 0.3on machine gun in the observer's position. It could also carry up to four 100lb bombs on wing racks.


Eighteen aircraft from the first order were completed as the O-2A, which carried night flying equipment.


Six more were completed as the O-2B, with dual controls but not guns. They were intended for use as command aircraft.


In 1926 Douglas built one civil O-2. This was ordered by James McKee, a pilot and business man from Pittsburgh who was planning to make the first float plane flight across Canada. The aircraft was given the designation O-2B Special, or O-2BS. It had all military equipment removed. McKee wanted the aircraft fitted with twin floats, as he would be crossed areas with many lakes and major rivers but few airfields. This meant that Douglas had to move the radiator from its normal position in a tunnel below the engine into a new position above the engine. This new vertical radiator would be adopted on the O-2C. The flight itself successfully took place in September 1926. Sadly McKee was killed in the following year while attempting to land a Vickers Vedette floatplane.


In 1926 Douglas received a second production order, this time for 46 O-2C aircraft. These used the vertical radiator of the O-2BS, and a slightly modified undercarriage and the gun fittings were different.

Nineteen of the forty-six aircraft went to the Air Corps while twenty-seven went to the National Guard. Eight more were ordered by Mexico, and two by the Navy, where they served with the Marine Corps as the OD-1.


The O-2D was an unarmed staff transport based on the O-2C. Two were built.


On earlier entries in the series the wings were linked by two struts per side while the ailerons were linked by a steel wire. On the single O-2E this was replaced with another strut, so the wings were now linked by three struts on each side. This change was adopted on the O-2H.


The O-2H saw such a major redesign of the aircraft that it really deserved a new number. The fuselage and tail were both modified. A new streamlined main undercarriage, with a single main leg and bracing replaced the tripod arrangement of earlier aircraft. Most dramatically the wings were totally redesigned. The equal span un-staggered wings of the original O-2 were replaced with unequal span staggered wings (with a 40ft 10in span on the upper wing and 38ft 6in span on the lower wing).

The inter-wing struts sloped forward and the third strut introduced on the O-2E was adopted as standard. The O-2H was powered by the Liberty engine, with the vertical radiator above the engine as used on the O-2C. The wing mounted fuel tanks were removed and a new tank was installed in front and below the pilot's cockpit. The O-2H has a two-blade metal propeller, replacing the wooden prop used on earlier models.

These changes meant that the O-2H was lighter than the O-2, 6mph faster, had a slightly better service ceiling and a much improved range, up from 360 miles to 512 miles.

The O-2H was produced in large numbers for the period, with ninety built for the Air Corps and fifty for the National Guard, for a total of 140 aircraft. Later in the production run the vertical tail surface was made shorter and wider, and the horizontal tail surfaces were also modified. All 140 aircraft were delivered in 1928-30.


The O-2J was an unarmed staff transported based on the O-2H. It was built in 1928, and at least one was used by General Fechet, Chief of the Air Corps. In order to increase safety the entire engine compartment could be flooded with pyrene to smoother any engine fire. Three were built.


The O-2K was based on the later version of the O-2H with the modified tail. Fifty seven were produced and given 1929 serial numbers. Thirty seven of these aircraft went to the Air Corps and twenty to the National Guard. They were intended to serve as staff transports and on liaison duties. In 1930 forty of the O-2Ks were turned into basic trainers, as the Douglas BT-1.

O-2 Derivatives

Thomas-Morse O-6

In 1926 Thomas Morse was asked to build two O-2s with an all-metal structure. Eventually they built five O-6s, which were O-2s with metal wings while the XO-6B was a smaller, lighter aircraft that served as the prototype for the Thomas-Morse O-19.


Three aircraft from the original order were completed with Packard 1A-1500 engines, as the O-7. They were later converted back into O-2s by giving them Liberty engines.


The O-8 was to have used an inverted Packard engine but the sole example was completed with a Curtiss radial engine. It was later converted to the O-2A standard.


The single O-9 was powered by a geared Packard 1A-1500 engine. It was later converted to the O-2A standard.


The O-14 was a scaled down version of the O-2H, with almost half of the gross weight and a less powerful Curtiss radial engine. It was sold into private hands in 1933.


The O-22 was an experimental development of the O-2H. The upper wing was swept back and N struts replaced the separate struts of the earlier aircraft. The two O-22s were powered by a Pratt & Whitney R-1340-9 radial engine and a number of different cowlings were tested on them.


The O-25 was an important production version of the family, and was similar to the O-2H but was powered by the Curtiss Conqueror V-1570 engine in place of the Liberty engine used on the O-2. Fifty were built with water cooled engines and thirty with Prestone-cooled engines.


The O-29 was a single staff transport, similar to the O-2K but powered by Wright radial engines, first the R-1750 and later the R-1820.


The O-32 was similar to the O-29, but with a 450hp Pratt & Whitney R-1340-3 Wasp radial. One O-32 and thirty O-32As were produced, but were soon converted into basic trainers as the BT-2 and BT-2A.


The O-34 was a single experimental aircraft with the N struts and swept back upper wing of the O-22, but with a Curtiss Conqueror engine in place of the Pratt & Whitney radial engine used on the earlier type.


The O-38 was the most numerous and final production version of the aircraft. It was similar to the O-25 and O-2H, but with a 525hp Pratt & Whitney R-1690 radial engine. The O-38 was also the basis of two export versions - Peru's O-2P and China's O-2MC.


One aircraft from the original contract for 75 was completed as an attack aircraft armed with eight machine guns. It competed against the Curtiss A-3 in 1926 but wasn't selected for production.


The OD-1 was the designation given to two O-2Cs ordered by the US Navy. They served with the US Marine Corps from 1929, briefly as observation aircraft but for most of their career as general utility aircraft.



Mexico ordered two batches of O-2s. The first batch consisted of eight O-2Cs. The second, which was produced in 1929, also consisted of eight aircraft, this time the O-2M which was based on the O-32A but with a 525hp Pratt & Whitney Hornet radial engine.


Peru ordered six O-2Ps, which could be equipped with floats or wheels and were used by their Naval Air Arm.


China was the main export customer for the O-2 family, buying 82 aircraft between 1930 and 1936. These aircraft were designated the O-2MC, but were based on the O-38.

Engine: Liberty V-1650-1 V-12
Power: 420hp
Crew: 2
Span: 39ft 8in
Length: 28ft 9in
Height: 10ft 6in
Empty weight: 3,032lb
Maximum take-off weight: 4,785lb
Max speed: 128mph
Service ceiling: 16,270ft
Range: 360 miles
Armament: One fixed forward firing 0.3in machine gun, one flexibly mounted 0.3in machine gun in rear position
Bomb load: Up to four 100lb bombs

Engine: Liberty V-1650-1 V-12
Power: 420hp
Crew: 2
Span: 40ft 10in
Length: 30ft 0in
Height: 10ft
Empty weight: 2,857lb
Maximum take-off weight: 4,550lb
Max speed: 134.5mph
Service ceiling: 16,900ft
Range: 512 miles
Armament: One fixed forward firing 0.3in machine gun, one flexibly mounted 0.3in machine gun in rear position
Bomb load: Up to four 100lb bombs

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How to cite this article: Rickard, J (2 March 2013), Douglas O-2 ,

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