The O-40 "Raven", offered by American aeroplane-maker Curtiss-Wright, began life as a biplane in its prototype stage. The aircraft was drawn up to fulfill a light-class, over-battlefield observation role for the United States Army Air Corps (USAAC) during the Inter-War period (that is, the period "between the wars"). The aircraft appeared as this single prototype example under the designation of YO-40 (Curtiss company Model 62) and sat a pilot and an observer in inline open-air cockpits (back-to-back) with construction of the aircraft being largely all-metal. Power was from a single Wright R-1820E "Cyclone" engine carried at the nose, driving a two-bladed propeller. A traditional over-under biplane wing arrangement (known as a "Sesquiplane", with the lower wing member considerably shorter than the upper member) was used while the undercarriage was made to be retractable. Of note was slight sweepback given to the upper wing member.
The first-flight of YO-40 was recorded in 1932 but this specimen was involved in a crash that May. The airframe was, for the most part, salvaged and this delay gave engineers the opportunity to enact changes to improve the design. Work resulted in a reinforced, stronger aircraft that now showcased enclosed cockpits for the crew and the changes were substantial enough to warrant the follow-up designation of "YO-40A". Additional work evolved the design even more, resulting in the complete deletion of the lower wing members and making the YO-40 a true monoplane (though it still retained its high-mounted upper wing member). The aircraft was now reborn through the "Y10-40B" line and this version was powered by a Wright R-1820-27 "Cyclone" 9-cylinder, air-cooled radial engine of 670 horsepower. The USAAC saw enough promise in the reworked design to order four examples based on the new standard.
As completed, the aircraft had an overall length of 28.9 feet, a wingspan of 41.7 feet, and a height of 10.7 feet. Empty weight measured 3,755lb against a Maximum Take-Off Weight (MTOW) of 5,180lb. Power from the Wright engine provided the aircraft with a maximum speed of 188 miles-per-hour, a range out to 325 miles, and a service ceiling up to 23,100 feet. Rate-of-climb was reported at 1,660 feet-per-minute.
Lightly armed by the design, the O-40 carried only two medium machine guns: 1 x 0.30 caliber Browning air-cooled machine gun in a fixed, forward-firing mounting (for the pilot) and a 1 x 0.30 caliber Browning air-cooled machine gun on a trainable mounting in the rear cockpit (for the observer and mainly intended for self-defense).
The aircraft were taken into Army service during June of 1933 and carried the formal designation of O-40B "Raven" for their time in the sky. The line served primarily with the 1st Observation Squadron (established March 1913 and, rather amazingly, still existing today as the "1st Reconnaissance Squadron"). Due to their limited inherent range, only these four models were procured by the service and the line was only operated into 1939. The aforementioned salvaged YO-40A prototype, post-revision, was destroyed back in 1938. As such, no Raven aircraft managed to survive by the time of World War 2 (1939-1945).