In May 1948 the US Navy's Bureau of Aeronautics issued the OS-113 requirement for an interceptor fighter capable of achieving 691 miles per hour (1,110 km/h) in level flight and reaching 50,000 feet (15,240 km) in just six minutes, as well as being able to achieve controlled diving flight at supersonic speeds at both medium and high altitudes. Seven companies -- Douglas (El Segundo), Grumman, Lockheed, McDonnell, North American, Republic, and Vought -- submitted bids for the OS-113 specification, a handful equipped with auxiliary rocket propulsion.
 |
| Left: Three-view drawing of the North American D-85 Right: D-85 interior arrangement |
North American's design for OS-113 was given the company designation D-85. It drew heavily upon experience gained by North American in design of the YF-93 penetration fighter, featuring a pair of scoop-style side intakes, and power was provided by one Westinghouse J40-WE-8 turbojet as well as one 1,500 lb (6.7 kN) thrust RMI A600C4 rocket motor. The D-85 was 51 feet 6 in (15.70 meters) long with a wingspan of 40 feet 6 in (12.34 meters) (23 feet 8 in [7.21 meters] when folded), a wing area of 425.92 ft2 (39.61 m2), a gross weight of 20,823 lb (9,445 kg), and a top speed of 632 miles per hour (1,017 km/h). When using the jet engine only, the D-85 could reach a top speed of 637 miles per hour (1,025 km/h) and had a gross weight of 19,993 lb (9,069 kg).
The rocket motor of the D-85 was primarily designed for the climb from 35,000 feet (10,668 meters) to 50,000 feet (15,240 meters), and when used in level flight, the D-85 could achieve 668 miles per hour (1,075 km/h) in a dive at the operational altitude. Armament for the D-85 comprised 24 unguided air-to-air rockets housed in a streamlined lower fuselage package placed roughly level with the wing root trailing edge. The pilot could select how many rockets to fire, and the complete firing cycle would take about 1.5 seconds, and like other OS-113 submissions, the D-85 could fire all its rockets within half a second.
In late 1948, the McDonnell Model 58 was selected over other proposals (including the D-85) and ordered into full-scale development as the XF3H-1.
