If we are looking at combat records, then all 4 listed fighters (P-51D, P-47N, F4U-4, or F6F-5) have one year or less in which to be considered.

The P-51 had a much smaller combat record in the PTO, with only P-51B/C models, and only in Burma… until the P-51D finally arrived in late 1944, which were first flown from re-captured Philippine bases. By that stage of the war, Japanese fighter opposition was rare, and Philippine-based Mustangs mostly performed close-support work. The only consistent fighter work the P-51D saw was during the B-29 escort missions (which it shared with the P-47N).

I agree with most of that, however P-51B/C’s were used a fair amount in China from 1944 (part of China-Burma-India theater but to distinguish from use of P-51A’s in Burma proper from 1943). And it met the Japanese Type 4 (aka Ki-84 Frank) there, the Japanese Army sent the Type 4 to China first in part to counter P-51’s.

Also PI based P-51’s did missions to Formosa, China coast etc at one way ranges up to ~800 miles. This is another point: range. The longest US fighter missions were flown by long range P-38’s up to ~900 mile radius, but 51’s and 47N’s came close (for example P-47N’s from Ie Shima to the Seoul area, that’s almost 800). There were remarkable ranges, however the Japanese themselves noted the greater persistence of USN fighters, especially over Japan, less of an eye on the fuel gauge (Iwo Jima based P-51’s were still ~600 over-water miles from home when they dropped tanks and started burning fuel at max throttle rate).

Also re: earlier comment P-38L’s flew some missions from Ie Shima/Okinawa base complexes to Japan proper in the final days of the war.

Another factor to consider is use by P-51D’s in very late war of very high octane fuel and high boost settings; they could considerably exceed the published P-51D stats or real performance experienced in ETO.

But as was said ‘best’ in WWII usually naturally focuses on ‘last’, what got in under the wire to fly a few missions at the end v what was just too late. It’s of limited meaning. Overall the P-38 was by far the most *important* USAAF fighter in the Pacific, and the F6F likewise for the USN, F4U for the USMC (USN F4U’s were also a quite late war thing, and even regular USMC F4U ops from carriers only began in January 1945).

Joe