The Cessna O-2 Super Skymaster was ordered by the U.S. Air Force in 1966 to replace the Cessna O-1 until a purpose-built aircraft could be put into service as a Forward Air Control and light observation aircraft. Because the Skymaster was a two seater, one crewmember could be freed from piloting the aircraft to concentrate on the difficult mission of Forward Air Control, which included such diverse tasks as marking targets for air strikes, giving strike briefings to incoming attack pilots, and avoiding ground threats. This made the O-2 ideal for the FAC mission, even if low-and-slow FAC pilots had to wait until the appearance of its successor, the OV-10 Bronco, to be protected by armor plating.

Other information:

http://en.wikipedia.org/wiki/Cessna_Skymaster

http://users.ids.net/~qam/AircraftPages/o2askymaster.html

http://www2.hurlburt.af.mil/library/factsheets/factsheet.asp?id=3432

http://www.skymaster.org.uk/history.asp