Light observation aircraft have had a role in major military powers of the world for over 100 years with their inherent ability to scan the battlefield. Qualities of such aircraft have always been simplicity, ruggedness, and operating weights that allow them to fly low-and-slow while maintaining a certain degree of survivability near contested zones. In the late-1960s, Cessna brought online an aircraft filling this description through its O-2 "Skymaster" series. The type went on to find success in the field, being produced in 513 examples from 1967 until 1975 and being operated by the likes of the United States Air Force (USAF) and others. The value of this aircraft was such that the service did not retire their final forms until 2010.
The O-2 was a direct military-minded offshoot of the civilian airspace Model 336 and Model 337 Skymaster / Super Skymaster, a lightweight aircraft intended for the "air taxi" role and produced to the tune of nearly 3,000 examples. The series was introduced in 1962 and enjoyed a long and healthy operating life for its time in the air with examples continuing to fly even today (2020).
The O-2 was developed from the Model 337 "Super Skymaster" form as a military platform for the Forward Air Control (FAC) role and other light duties. The USAF approached Cessna in 1966 to bring about the form as a successor to its aging fleet of O-1 "Bird Dog" light, high-winged aircraft in active service since the Korean War (1950-1953). Since the conversion would be relatively easy, cost control was central to the acquisition of the new aircraft and the Super Skymaster fulfilled the requirements needed by the service.
Like the Bird Dog, the Super Skymaster offered excellent low-and-slow control capabilities and short-field operation. This was aided by the shoulder-mounted wings braced along the top of the fuselage. The high-wing mounting also provided exceptional vision out-of-the-cockpit for the pilot and passenger. The airframe housed two engines, the first seated in the nose in the usual way and driving a simple two-bladed propeller while a second unit was buried in the aft-fuselage section to drive another propeller unit in "pusher" configuration. The tail unit consisted of twin booms extended from the wing mainplane members and joined together by a shared horizontal plane at the rear. Each boom was capped at its end by a vertical tail fin. A tricycle undercarriage, retractable, was used for ground running.
Power for the aircraft consisted of paired Continental IO-360C/D flat-six air-cooled engines, each developing 210 horsepower. This "push-pull" arrangement provided the aircraft with a maximum speed of 200 miles-per-hour, a cruising speed near 145 mph, a range out to 1,060 miles, and a service ceiling of just under 20,000 feet. Rate-of-climb reached 1,180 feet-per-minute.
Between the civilian version and militarized form, the O-2 differed in having foam-insulated fuel tanks (wing-mounted), special-mission equipment and navigational gear, additional viewing ports, and side-by-side seating for two (instead of six total). The changes resulted in an increase to weight by 1,000lb which, in turn, resulted in reinforcement being added to compensate.
First USAF examples were taken into service in 1967 and ex-USAF/ex-USN airframes arrived for the U.S. Army shortly thereafter. The type went on to see extensive service in the Vietnam War (1955-1975) where its FAC capabilities were truly put to the test. Some were specially-modified for the PSYchological OPerationS (PSYOPS) role. During the conflict, losses of O-2 platforms totaled 178 airframes. Before the end, some of the fleet (perhaps as many as 35 units) was transferred to the Republic of Vietnam Air Force.
The United States Navy also utilized the type from 1983 onwards where they were operated as range controllers. The fleet was eventually succeeded by the Beechcraft T-34 "Turbomentor" in same role.
Two major production models of the O-2 Skymaster series were realized, O-2A and O-2B. A-models were the initial forms and manufacture totaled 513 examples. For the FAC role, the aircraft could be outfitted with various light ordnance including gun pods, rocket pods, and flare dispensers. The B-model series were reserved for the aforementioned PSYOPS role used in Vietnam. These unarmed variants were outfitted with loudspeakers and leaflet dispensers for the role. At least 31 examples of the stock came directly from civilian market Model 337 airframes that underwent conversion.
Beyond the United States and its various military services, the O-2 was operated by the powers of Botswana, Costa Rica, the Dominican Republic, the Ivory Coast, Haiti, Iran, Namibia, El Salvador, the Solomon Islands, South Korea, South Vietnam, Thailand, Uruguay, and Zimbabwe. El Salvador deployed armed forms during the Salvadoran Civil War (1979-1992) for both direct-attack and observation.
Some ex-U.S. military models from the Vietnam Conflict were refurbished and placed into service with the California Department of Forestry and Fire Protection where they operated from 1976 until the mid-1990s.
The O-2's role was eventually taken up by the Rockwell OV-10 "Bronco" straight-winged platform which performed excellently for its own time in the air and is detailed elsewhere on this site.