The O-1 was developed from the commercial Cessna Model 170 (originally designated L-19s) and were used by the USAF, Army and Marine Corps for such tasks as artillery spotting, front-line comms, medivac and pilot training. In SE Asia they were also deployed on FAC duties but they were slow, lacking range and proved vunerable to ground fire. This led eventually to their replacement with O-2 Skymaster and OV-10 Bronco. This Bird Dog came to the National Museum of the USAF for display in 1971.