The Bronco began with a specification approved by the U.S. Navy, Air Force and Army, a "tri-service" specification called "LARA" (the Light Armed Reconnaissance Aircraft), issued at the end of 1963. LARA was based on a perceived need for a new type of "jungle fighting" versatile light attack and observation aircraft. Existing aircraft (the O-1 Bird Dog and O-2 Skymaster) were perceived as obsolescent, with too small a cargo capacity for this flexible role.
The specification called for a twin-engined, two-man aircraft that could carry at least 2,400 lb (1,100 kg) of cargo, six paratroops or stretchers, and be stressed for +8 and -3 Gs (basic aerobatic ability). It also had to be launchable from an aircraft carrier, fly at least 350 mph (560 km/h), take off in 800 feet (240 m) and convert to an amphibian.
Various armament had to be carried, including four 7.62 mm machine guns with 2,000 rounds, and external weapons including a 20 mm gun pod and Sidewinder missiles.
Eleven proposals were submitted, and seven made the first cut: the Beech PD 183, Douglas D.855, General Dynamics/Convair Model 48 Charger, the Helio 1320, the Lockheed CL-760, a Martin design and the North American/Rockwell NA300.
In August 1964, the NA300 was selected. A contract for seven prototype aircraft was issued in October 1964.
General Dynamics/Convair protested the decision and built a prototype of the Model 48 Charger anyway, which first flew on November 29, 1964. This was also a twin-boom aircraft that had a broadly similar layout to the Bronco. The Charger, while capable of outperforming the OV-10 in some respects, crashed on October 19, 1965 after 196 test flights. Convair dropped out of contention.
From Wikipedia