The Thomas-Morse O-23 was a version of the successful O-19 observation aircraft that was powered by a Curtiss Conqueror engine, making it the first member of the O-19 family to be powered by an inline engine since the original O-6 prototypes.
Early in 1926 Thomas-Morse had been given a contract to produce two examples of the Douglas O-2 observation aircraft, but with a metal structure for the wing in place of the wooden one of the O-2. These aircraft, the O-6, were powered by the inline Liberty engine, and were completed during 1926, but no orders followed. Thomas-Morse decided to produce their own design, the XO-6B, which was purpose built to benefit from the all metal framework, and was powered by the Pratt & Whitney Wasp R-1340 radial engine. This time the USAAC was impressed, and on 16 June 1928 placed an order for four examples of the new aircraft, as the O-19.
On 3 November 1928 the USAAC placed a second order, for a single aircraft to be powered by the Curtiss Conqueror inline engine, with the designation O-23. This was in addition to the original four aircraft, and was given the USAAC serial number 29-352. In December 1928 another two engine test beds were ordered, but this time two of the original four aircraft were used as their basis.
The O-23 was powered by the 600hp Curtiss Conqueror V-1570-1, a water cooled inline V-12 engine. The Conqueror required a large air intake under the engine, and on the O-23 this was carried in a rather ungainly looking fairing that jutted out below the general lines of the fuselage. The Conqueror wasn’t a terribly successful engine, although it was used in a series of military aircraft of the late 1920s.
The O-23 was otherwise similar to the standard O-19, with an all metal framework, a corrugated metal covering for the fuselage and fabric covered sings. It carried a crew of two in separate cockpits, each with a small windscreen. In September 1929 it underwent tests at McCook Field as the P-562.