In the late 1940s the US Army issued a specification for a two-seat liaison and observation monoplane. From the submissions received from manufacturers that of the Cessna Aircraft Company was declared the winner and in June 1950 an initial contract was awarded for 418 examples of the aircraft, which the company identified as the Cessna Model 305A.
Cessna's design was based upon the successful Model 170, a light-weight strut-braced high-wing monoplane, powered by a 108kW Continental flat-six engine, which provided accommodation for a pilot and three passengers. The Model 305A differed by having the aft fuselage redesigned to give a clear view to the rear and by the provision of transparent panels in the wing centre-section, which formed the cabin roof. A wider access door gave room to load a standard stretcher, for which support brackets were installed.
Deliveries of production aircraft began in December 1950, under the designation L-19A and with the name Bird Dog, and by October 1954, 2,486 had been delivered, of which 60 where diverted to the US Marine Corps which designated them OE-1. An L-19A-IT instrument trainer version was developed in 1953, TL-19D trainers with constant-speed propellers appeared in 1956 and improved L-19E, of higher gross weight, was the final version to bring total production of Bird Dogs to 3,431. With rede-signation in 1962, the US Army's L-19A, TL-19D and L-19E aircraft became O-1A, TO-1D and O-1E respectively. The US Marines' OE-1 became O-1B and this service also acquired 25 of the higher-powered O-1C. US Army trainers, derived from standard production aircraft, had the designations TO-1A and TO-1E.
Bird Dogs were operated in small numbers during the Korean War, but the US Air Force acquired many of the US Army's O-1s for use by forward air controllers in Vietnam; former TO-1Ds and O-1As were redesignated O-1F and O-1G respectively when equipped for this role. In addition to being supplied to many nations, O-1s were also built under licence by Fuji in Japan.
