P 40F and the Pacific.

[shooshoobaby]

It was the lack of a 2 Stage SuperCharger that prevented the P - 40
from being a High Altitude Fighter.
Cheers

[Graham Boak]

Although the Merlin in the P-40F was only fitted with a single-stage supercharger, it did (I believe) have a higher full throttle height than the equivalent Allison. It is my understanding that for this reason the P-40F was preferred for fighter units, whereas the Allison-engined variant was more used as a fighter-bomber. When such differentiation was possible, of course. Although not the best fighter in theatre, the Merlin P-40F did a respectable job.

One reason for using it in the western theatres is that Merlin-trained engine fitters were not common in the USAAF, and it made sense to concentrate their use where expertise and spares were most readily available.