The Douglas O-38 was numerically the most important in the family of biplane observation aircraft that began with the Douglas O-2. The O-2 began life as a single bay biplane with un-staggered equal span wings in 1925. It was followed by the O-2H, with staggered unequal span wings, and the O-25, which saw the Liberty engine of the O-2 replaced with the Curtiss Conqueror inline engine.
The O-38 was similar to the O-25, with the same staggered unequal span wings, steel tube structure for the fuselage, wooden wings and fabric covering, but it was the first major production model in the series to be powered by a radial engine, in this case the Pratt & Whitney R-1690.
The O-38 was unusual in that there was no prototype. The first twelve O-38s were produced in a block in 1930, and production for the US Military continued into 1934. The O-38 was also the base for the most numerous export models - six O-38Ps that went to Peru and 82 O-2MC produced for China.
The O-38 was actually a little slower than the O-25A (top speed of 150mph, down from 156.6mph) and had a lower service ceiling (19,000ft down from 22,180ft).
The O-38 began to enter service in 1931, supplementing the earlier O-2 and O-25. The National Guard was a major user of the type, receiving forty-five O-38s, one O-38A, thirty-three O-38Bs, one O-38D, thirty-seven O-38Es and eight O-38Fs from their own orders as well as a number of ex Air Corps aircraft. From 1929 each National Guard squadron was meant to have five standard observation aircraft and the O-38 was one of the most common types issued. This rose to eight aircraft in 1933, with the O-38E playing a major part.
The O-38 was used in the 1931 air manoeuvres, which took the form of a series of demonstrations for the public. The Air Corps only just had enough aircraft for an impressive demonstration and so three squadrons of O-38s were pressed into service as bombers!
In February 1934 the Air Corps temporarily took over the delivery of Air Mail within the United States. Both the O-38B and O-38E were used to carry the mail. The O-38E, with its enclosed cockpit, wasn't popular in this role as the canopy was believed to restrict the pilot's view at night and in the difficult country around Cheyenne, where many of them were operating. The O-38E also suffered two fatal accidents at Cheyenne, on 9 March and 16 March. The weight of the mail had disrupted the balance of the aircraft too much, and the O-38E was withdrawn from the mail run.
The Chinese O-2MCs had a short service career. Once conflict broke out between Japan and China they were overwhelmed by superior Japanese fighters.
Forty five O-38s were produced in 1930 and 1931. They were armed with one fixed forward firing machine gun and one flexibly mounted machine gun. All forty five aircraft went to the US National Guard. They were powered by the 525hp Pratt & Whitney R-1690-3 radial engine, with a Townend ring and two-blade metal propeller.
One O-38A was produced for the National Guard in 1930. It was an unarmed staff transport version of the basic O-38.
The O-38B was identical to the O-38 apart from a minor change to the engine - the R-1690-3 of the O-38 was replaced by a similar R-1690-5. Thirty were produced for the Air Corps in 1931 and another thirty-three went to the National Guard in 1932-33.
One of the National Guard aircraft was later given a 600hp Pratt & Whitney Hornet C engine and the canopy used on the O-38S. Two of the Air Corps aircraft went to the Bureau of Air Commerce.
In 1932, at the end of the Air Corps' five year expansion plan, the O-38B was one of several types judged to be of 'standard' quality - good enough for front line service.
The O-38C was a single example of the O-38B that was ordered for the US Coast Guard in 1931. Minor equipment changes resulted in the change of designation. It was the ninth aircraft to reach the Coast Guard, and was originally given the serial number CG9. In 1936 this was changed to V108.
The O-38S was a private venture development of the aircraft. It had a wider and deeper fuselage, streamlined wing struts and a sliding canopy that covered both cockpits. It was powered by a 575hp Wright R-1820-E radial engine with a smooth cowling. Douglas tested it with a variety of propeller, and it was also tested by the Material Division of the War Department. In October 1932 it was purchased by the War Department and became the O-38D.
The O-38D was the designation given to the private venture O-38S after it was bought by the US War Department in October 1932. It was then used by the Militia Bureau, which ran the National Guard.
The O-38E was the main production version of the private venture O-38S. It had the same wider and deeper fuselage used on that aircraft, and the same modified wing struts. The main differences were the use of a 625hp Pratt & Whitney R-1690-13 radial engine which required a modified cowling and powered a three bladed propeller. The canopy was cut down to only cover the front cockpit, and the normal flexibly mounted machine gun was installed on the rear cockpit.
Thirty seven O-38Es were ordered in two batches (aircraft 33-002 to 33-016 and 34-001 to 34-022), all for the National Guard. The second of these contracts, No.5991, issued on 10 August 1933, was the last War Department for Douglas biplane observation aircraft (the O-38F was ordered between the two batches of O-38Es).
The O-38E could use twin Odo floats, and at least one aircraft from the Indiana National Guard was operated in that configuration.
The O-38F was an unarmed version of the O-38E. Eight were ordered between the two batches of O-38Es. The O-38F was powered by a Pratt & Whitney R-1690-9 radial engine, and because it was unarmed could be equipped with a canopy that covered both cockpits.
Six O-38Ps were exported to Peru in 1932. These were similar to the O-38E with the larger fuselage, and could use either wheels or floats. They were operated by the Aviacion Naval Peruana.
China was the main export customer for the O-38 and purchased 82 of them over six years.
The O-2MC was powered by an un-cowled 525hp Pratt & Whitney Hornet A radial engine. Ten were produced.
They were followed by twenty O-2MC-2s, which had the same engine but with a Townend ring.
Five O-2MC-3s were produced, powered by the 575hp Hornet BG1 radial.
Next were twelve O-2MC-4s
They were followed by twelve O-2MC-5s, which used the 420hp Pratt & Whitney Wasp C1 engine.
The last large order was for 22 O-2MC-6s, powered by the 575hp Wright R-1820-E radial engine.
One O-2MC-10 was produced, powered by a 670hp Wright R-1820-F21 radial engine.
Engine: Pratt & Whitney R-1690-3
Span: 40ft 0in
Length: 31ft 0in
Height: 10ft 8in
Empty weight: 3,080ft
Maximum take-off weight: 4,343ft
Max speed: 150mph
Service ceiling: 19,000ft
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