UNITED STATES MILITARY AIRCRAFT by Jos Heyman Air Force O = Observation (1924-1942) Last update: 1 February 2015 O-1 Curtiss 37 Falcon Specifications: span: 38'. 11.58 m length: 27'9", 8.46 m engines: 1 Curtiss V-1150 max. speed: 143 mph, 230 km/h (Source: Gordon Hubbard, via 1000aircraftphotos.com photo #3375) Based on the Falcon series of aircraft, the XO-1 was fitted with a Liberty V-1650-1 engine and had a length of 28'7", 8.71 m. A single example was built with serial 23-1252 and was entered in the 1924 and 1925 design competitions. It was later fitted with a Packard 1A-1500. Eventually it was redesignated as ZXO-1. The first production version was the O-1, to which the specifications apply. 10 aircraft were ordered with serials 25-325/334. Of these aircraft 25-333 was converted with a Liberty V-1650-3 engine and was redesignated as O-1A . It was also known as XO-1A. 25 examples of the O-1B version were ordered with serials 27-263/287. They were basically similar to the O-1 but had a V-1150-5 engine and a length of 27'3", 8.31 m. Those remaining in service were eventually redesignated as ZO-1B . Four aircraft were converted as O-1C as staff transports with side by side seating in the rear cockpit. They had serials 27-264, 27-266/268. Those remaining in service were eventually redesignated as ZO-1C. A projected version of the O-1C, to be known as the O-1D , was to have a V-1150-7 engine but was not built. The O-1E version had a length of 28'4", 8.64 m and a V-1150-5 engine. 36 were built with serials 29-282/287 and 29-289/318 whilst a batch with serials 29-319/322 was converted to YO-13C and Y1O-26 before completion. In addition an A-3B with serial 30-001 was converted to this standard. One aircraft, with serial 29-288 was ordered as O-1E but was completed as the O-1F unarmed communications aircraft. One O-1E with serial 29-295, was tested as XBT-4 and yet later converted as XO-1G as Curtiss model 38. It was later redesignated as Y1O-G and eventually as O-1G . In addition 30 O-1Gs were built with serials 31-472/501. These were similar to the O-1E but had a length of 27'4", 8.33 m. Those remaining in service were eventually redesignated as ZO-1G. Several aircraft were flown with Wright Field serial numbers: 23-1252 as P-375, 25-325 as P-437, 25-333 as P-449, 25-334 as P-440, 27-267 as P-558, 27-268 as P-497, 27-276 as P-532, 27-277 as P-596, 29-282 as P-587 and an unknown aircraft as P- 484. Refer also to A-3, A-4, A-5, A-6, BT-4, O-11, O-12, O-13, O-16, O-18, O-26, O-39, F8C O-2 Douglas Specifications: span: 39'8", 12.09 m length: 29'7", 9.02 m engines: 1 Packard 1A-1500 max. speed: 150 mph, 241 km/h (Source: Pat Loop, via 1000aircraftphotos.com photo #5378) Based on the US Navy’s DT design a single XO-2 prototype was tested with both a long and a short span and was initially fitted with a Liberty V-1650-1 before the 1A-1500 engine was installed. It had a length of 29'3", 8.92 m. The serial was 23-1251. Some reference sources have suggested that the Dayton Wright XO-3 with serials 23-1254 was also an XO-2. The initial production version was the O-2, to which the specifications apply. 46 were built with serials 25-335/380 whilst O-7s with serials 25-406 and 25-407 were also converted to this standard. The O-2A version was fitted for night flying but was otherwise similar to the O-2, 18 were built with serials 25-387/404. O-2As with serials 25-405/407 were completed as O-7. In addition an O-2A with serial 25-408 was converted to O-8 before being converted back to O-2A. Finally, O-2C 25-409, which had been converted to O-9, was also converted to the O-2A standard. After having provisionally been designated as XO-2B , six O-2B dual control aircraft were built with serials 25-381/386. The O-2C version incorporated various improvements and 33 were built with serials 26-386/418 and 25-409. Also O-7 25-405 was converted to this standard. One of the aircraft, with serial 26-387 was used for experimental purposes with designation XO-2C . The designation O-2D was assigned to an unarmed staff transport and two were built with serials 26-419/420. In 1927 a single O-2C with serial 26-418, was fitted with a different tail arrangement and was redesignated as XO-2E . On completion of tests it was redesignated as O-2E . The O-2F and O-2G designations were reserved for projected versions which were cancelled. The O-2H version had a span of 40', 12.19 m, a length of 30', 9.14 m, a Liberty V-1650-1 engine and a max. speed of 133 mph, 214 km/h. 141 were built of this version with serials 27-288/297, 28-128/187, 28-349/358, 29-158/178, 29-342/351 and 29-375/404. One of these aircraft, 29-164, was later converted as O-25. Another aircraft was flown as XO-2H . A staff transport version of the O-2H was designated as O-2J and three were built with serials 28-127, 28-188 and 29-209. The O-2K version was based on the O-2H but had minor improvements. 59 were built with serials 29-179/208, 29-210/218 and 29-413/432. 40 of these were later converted to BT-1. The O-2M version was supplied to Mexico and was not ordered through US military agencies. Several aircraft were flown with Wright Field serials: 23-1251 as P-374, 23-1251 as P-519, 25-350 as P-441, 25-353 as P-465, 26-387 as P-458, 26-418 as P-466 and unknown aircraft P-467, P-468, P-481, P-482, P-492, P-512, P-514, P-521, P-525 and P-529. Refer also to A-2, BT-1, BT-2, O-7, O-8, O-9, O-14, O-22, O-25, O-29, O-32, O-34, O-38, OD O-3 Dayton Wright Specifications: span: 45', 13.72 m length: 31', 9.45 m engines: 1 Wright V-1950 max. speed: 146 mph, 235 km/h (Source: D. Abel, via Aerofiles.com) One XO-3 was ordered with serial 23-1254. It was also flown with Wright Field serial P-376 but was returned to the manufacturer on 30 April 1925, presumably cancelled. Some references show this as a Wright design. It seems that after the demise of Dayton Wright, the XO-3 was completed by Wright Aeronautical. Other reference sources have suggested that 23-1254 was a Douglas XO-2. O-4 Martin 71 Specifications: span: length: engines: 1 Liberty V-1650-1 max. speed: One XO-4 was ordered with serial 23-1255 but was subsequently cancelled. O-5 Douglas Specifications: span: 50', 15.24 m length: 38'11", 11.86 m engines: l Liberty V-1650-1 max. speed: 107 mph, 172 km/h (Source: TKnl, via Aerofiles.com) Based on the DT design, six XO-5s were ordered as Douglas Observation Seaplane (DOS) but were designated as O-5 before delivery. The serials were 24-002/007. O-6 Thomas Morse Specifications: span: 39'9", 12.12 m length: 28'8", 8.74 m engines: 1 Liberty V-1650-1 max. speed: 129 mph, 208 km/h (Source: USAAC McCook) The XO-6 was a metal version of the O-2 design and two were built against an order which had been placed on 21 April 1926. The serials were 25-435/436 and they were also flown with Wright Fields serials P-439 and P-456 respectively. Three examples of the O-6 were built with serials 25-437/439. Whilst the O-6A designation was not assigned, the XO-6B designation was used for an extensively redesigned version with a Pratt & Whitney R-1340 engine. Although the aircraft, with serial 25-440, was not accepted, it was tested with Wright Field serial P-503 and eventually evolved into the O-19 design. Refer also to O-2, O-19 O-7 Douglas Specifications: span: 39'8", 12.09 m length: 29'6", 8.99 m engines: 1 Packard 1A-1500 max. speed: 137 mph, 220 km/h (Source: Gordon Hubbard, via 1000aircraftphotos.com photo #3405) Three O-2As were completed as O-7. Of these two were later further converted to O-2 standards and one to O-2C standards. The serials of these aircraft were 25-405/407. Aircraft 25-405 and 25-407 were also flown with Wright Field serials P-432 and P-459 respectively. 25-405 was eventually converted as an O-2C whilst 25-406 and 25-407 were converted to O-2 standards. Some reference sources claim that only one aircraft (25-409) was involved.