I have read that the US Navy worked with P&W to come up with a two-stage supercharger that was used on the F4U Corsair (and probably others).
Did this make a big difference? I know that the USAAF wanted to put turbochargers on the P-70 (night fighter variant of A-20) but they were not available (higher priority for bombers, P-47s and P-38s). I was thinking that if the Army had access to the Navy's supercharger, maybe it would have been more successful, not to mention that it could have benefited other planes....