The Cessna O-1 Bird Dog is a liaison and observation aircraft that first flew on December 14, 1949, and entered service in 1950 as the L-19 in the Korean War. It went to serve in many branches of the U.S. Armed Forces, was not retired until the 1970s in a number of variants, and also served in the Vietnam War. It was also called the OE-1 and OE-2 in Navy service, flying with the Marine Corps, and in the 1960s it was re-designated the O-1. It remains a civilian-flown warbird aircraft, and there are examples in aviation museums. It was the first all-metal fixed-wing aircraft ordered for and by the United States Army following the Army Air Forces' separation from it in 1947. The Bird Dog had a lengthy career in the U.S. military as well as in other countries, with over 3400 produced.

The SIAI-Marchetti SM.1019 is an Italian STOL liaison monoplane built by SIAI-Marchetti for the Italian Army. It is a turboprop-powered derivative of the Cessna O-1 Bird Dog.