The Ki-84 Type 4 Hayate (Gale) was "the most outstanding Japanese Army Fighter and far ahead of the Oscar, Tony and Tojo... potentially the most dangerous Japanese army fighter plane," according to a mid-1945 U.S. AAF evaluation. The Frank was one of the most formidable Japanese aircraft of the war, being able to out climb and outmaneuver both the US P-47N Thunderbolt and the P-51H Mustang fighters. It was also employed as a fighter-bomber.

The Frank made its combat debut in Aug. 1944 against AAF aircraft over Hankow, China. The aircraft was also flown extensively in the 1944-1945 Philippines campaigns, and in the Okinawa operation. The plane was initiated during a period of "easy victories," according to aviation historian William Green, because the Japanese Army Air Force "was sufficiently realistic to see that its ascendancy could not be maintained indefinitely unless superior warplanes were introduced." The Nakajima prototype flew in April 1943, fifteen months after design had started. The first production model, the Ki-84-I, totaled 3,510 aircraft, including 100 built by the Manchurian Aircraft Manufacturing Co. US air attacks against the engine and airframe plants severely reduced production, but it continued until almost the end of the war. A variety of advanced models were developed, most with improved engines, but they were developed too late to go into production.

The Frank, which resembled the Oscar, was a low-wing monoplane with bubble canopy. The aircraft was well liked and simple to fly, although taxing and ground handling were generally poor. The Ki-106 was an effort to produce the Frank largely of wood. Flown for the first time in July 1945, the plane was heavier and more sluggish than the metal Ki-84. Only three prototypes were built.

The Ki-84-Ia was capable of 388 mph and had a maximum range of 1,025 miles with internal fuel tanks and 1,815 miles with drop tanks. Armament of the Ia consisted of two 20 mm cannon and two 12.7 mm machine guns; the Ic had two 20 mm and two 30 mm cannon. In the fighter-bomber role, two 551 lb bombs could be carried on the wing racks