USN official A/c characteristics booklet for F6F-5 dated November '45* gave top speed as 378mph at combat power=WEP at 18,000ft. However, AFAIK 409mph at 21,600ft (presumably at WEP) was a real number obtained by a production F6F-5 in trials v a captured Zero Model 52 and F4U-1D (which topped out at 413mph at 20,400, much closer to the F4U-1D's official max of 409 at 19.9k ft, per ACP dated Jan '45). As with some Japanese fighters, USN fighter official top speeds may have been considerably conservative in some cases. I suppose zero-length rocket rails or other pertuberances fitted or not also affected these numbers.409 mph is very fast for a F6F-5 (for the USN the F-5 with racks go to 330 knts and for FAA go to 392 mph (probably w/o racks))
Tillman said in "Hellcat" that some units believed the -5 was both faster and climbed better than the -3, though according to official stats (comparing to F6F-3's ACP dated Oct '45), -5's best speed was only 6mph higher than -3's, and time to climb to both 10k and 20k ft definitely longer. Tillman himself quotes yet again different speed for the two versions, 388mph @ 25k ft for -3, 400mph @ 20k ft for -5, but gives no original source.
*by then the standard armament of F6F-5 was 4*.50 cal and 2*20mm but this weight and drag (of the barrels and fairings of 20mm) difference would not explain such a speed difference by itself.
Joe
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