Bad -ass of the Pacific February 10 2015
Since Pear Harbor in 1941 to the end of the war in 1945 the Japanese fielded one single fighter (other than the Oscar), that being the Mitsubishi Zero. By the end of WWII, the Americans in the Pacific Theater and in particular the Navy/Marines had fielded at least 4 different type of fighters; the most capable one (in my personal opinion) being the F-4U Corsair. The Corsair made use of the biggest engine available, the same one used by the P-47 Thunderbolt and by the F6 Hellcat (also in the Pacific Theater).
Let us not forget that from Pearl Harbor to May 1942 war against Japan was never a "sure thing", America did not know who was going to win. From Pear Harbor till The Battle of Coral Sea in May 7-8 of 1942, the Japanese had been victorious at each battle. It was at the Battle of Coral Sea that the tide turned (slightly, only, as one could argue that it was really a tie.) in favor of the Americans. From that point on, the Japanese never had a major victory. The newer planes as the Corsair and the Hellcat contributed greatly to that. By that time, naval battles were no more ships vs. ships, but airplanes vs. ships.
Airplanes had to go bomb the enemy's ships and in turn the enemy's fighter were defending their fleet. By the time the Hellcat and the Corsair were fully deployed, the Zero was at a great disadvantage. American planes were faster (but not more agile), had greater fire power, its pilots were better protected by armor, the tactics more effective (negating any advantage on agility) and more importantly, American pilots were actually more experienced and veterans from previous campaigns (no so the case with ill trained Japanese pilots).