[rmlew]

One of the things about the Flying Tigers unit was they discovered how to defeat the Mitsubishi A6M "Zero"--just out-dive them. And it was this unit that discovered the "Zero" was extremely vulnerable to gunfire from any well-armed fighter.
1. The AVG flew against few Zeros. They ran up against Oscars all the time. Of course AVG vets like Pappy Boyington later dealt with Zeros all the time.
2. Chennault figured the flaws in Japanese Aircraft designs flying 2 years before. He trained the AVG not to dogfight and to use two-plane formations.
3. The person who really taught the Navy and Marines how to defeat the Zero, or at least match it in Wildcats was Lt. Commander James Thach with his eponymous "Thach Weave". He tested it with Lt. Edward "Butch" O'Hare. Everyone remembers O'Hare because of the airport and his unrelated Medal of Honor. Few remember Thach, but he saved that lives of hundreds of American aviators and sailors with this and with his later work in developing the defenses against Kamikaze attacks. Having an Arleigh Burke flight III air defense destroyer named after him would be fitting.

[RayChuang88]

The biggest problem with both the Ki. 43 "Oscar" and the A6M "Zeke" was the complete lack of armor protection, not to mention even the P-40 could out-dive both planes. That's why once the Grumman F6F Wildcat became widely available the Japanese suffered very heavy combat losses in air combat.