The Mitsubishi Ki-83 was designed as a long-range heavy fighter. It was designed and built by a team led by Tomio Kubo, the designer of the highly successful Mitsubishi Ki-46 "Dinah". The design was a response to a 1943 specification for a new heavy fighter with great range. The first of four prototypes flew on 18 November 1944. The machines displayed remarkable maneuverability for aircraft of their size, being able to execute a 671 m (2,200 ft) diameter loop in just 31 seconds at a speed of over 644 km/h (400 mph). The Ki-83 carried a powerful armament of two 30 mm (1.18 in) and two 20 mm cannon in its nose. Plans for the Ki-83 to enter series production within the bomb-ravaged Japanese industrial complex were underway when Japan surrendered on 15 August 1945. The Ki-83 was a total surprise to the Americans who, unaware of its existence, had not given it a code name as they had to all other known Japanese World War II aircraft. Following the war, American aeronautical engineers and American Air Force officials evaluated the four prototype machines with great interest. In the evaluation flight, Ki-83 recorded 762 km/h (473 mph) top-speed at altitude 7000 m (23,000 ft) with American high-octane fuel. In fact, most of the known photographs of the Ki-83 show it wearing USAAF insignia.