Cessna O-1G Bird Dog The O-1G was a two-place observation and liaison aircraft developed from the commercial Cessna Model 170 in 1949. Originally designated L-19s, Bird Dogs were used by the U.S. Air Force, Army and Marine Corps for such tasks as artillery spotting, front-line communications, medical evacuation and pilot training. In Southeast Asia, the O-1s became a USAF forward air control aircraft. A forward air controller (FAC), often an experienced fighter pilot, flew in a specific geograph