I found this exerpt from Fire In The Sky :
The end product was the Nakajima Ki43 (Allied code name: Oscar; Peregrine Falcon to the Japanese). Although it followed the path of the successful Zero in many respects, the low-weight/high-maneuverability formula lost coherence in this design. Oscar was the lightest fighter used by any major combatant during World War II, weighing almost 800 pounds less than the delicate Zero. Like the Zero it was designed to maximize lift and maneuverability. Oscar was the most nimble fighter to serve in the war, superior to the Zero itself in this regard. Very maneuverable and possessing an excellent rate of steep climb, Oscar was a frustrating opponent. Like all fighters that served in the Pacific, the Ki43 was dangerous if the circumstances favored its pilot. While flying his powerful P 38 Lightning, American ace Perry Dahl had a confrontation with an Oscar in the fall of 1943 over New Guinea:
There were four of us one day that caught one little lone Oscar, and that was the lightest, most maneuverable fighter they made--it only had two .30-caliber guns on it--but we made passes on that Oscar for over forty minutes. I came home with a hole in my prop--we never touched him. It was just remarkable. This guy was so sharp. When you’d line up and start to fire he could turn into you, he could dance on the rudders, and just turn around and fly back almost underneath itself. And all four of us just gave up and flew back home.
Robert DeHaven, one of the top 5th USAAF aces, recalled the almost phenomenal maneuverability of the Oscar. The maneuver he describes, the Immelmann turn (named after World War I German ace Max Immelmann), was a challenging maneuver for any World War II fighter. It required that the aircraft go into a steep climb, change direction, and level out going on a different course (essentially a half-loop upward followed by a half-roll). Because of the steep climb, the gain in altitude was paid for by a sharp decrease in speed. As DeHaven recounts, the Oscar was so light and nimble that it could complete an Immelmann and then quickly do a second, even followed by a hammerhead stall, which requires a pilot to raise the nose, kick the rudder, and descend downward in a stall. This maneuver, following a double Immelmann, is the sort of thing that thrills modern airshow crowds observing featherlight acrobatic aircraft. No military aircraft during World War II was capable of this complicated move except the Oscar:
You’d be lucky to get one Immelmann out of a [Ki61] Tony starting from an initial flight attitude, whereas an Oscar, it really could do a double, and I saw it happen too many times. I’m not too sure that a Zero, unless he had proper conditions set up, maximum throttle, and all-out level flight, could do it. But I saw an Oscar do several double Immelmanns, even topped off by a hammerhead stall. That’s pretty fancy to watch. It was an enormously maneuverable airplane. The Oscar was designed to be an army fighter for the Manchurian and Chinese theaters. It had great maneuverability but with its armament of two machine guns, it wasn’t too far from the Sopwith Camel era in some ways.
Like Dahl, DeHaven led a flight four U.S. aircraft (P 40s) against a well-flown Oscar and came away empty: "There were four of us against an Oscar. The pilot was a master. As I made a pass he’d turn straight into me. I spread my flight out, so there was no possible place for him to turn, but he was too good. I got a snapshot and that was it. After the fourth attempt I broke off the attack. We were getting low and were near the Japanese base. The possibility of being jumped by Japanese from above argued for prudence."
