The problem with the P-40 was lack of horsepower. Had it been equipped with a 1700HP engine, it'd be a whole different plane. The Allison, as spec'd by the U.S. military, was equipped with a single speed single stage crank driven supercharger. For the P-38, a GE turbocharger was added. Originally, the same turbocharger was spec'd for the P-39, but the USAAF had it deleted. So it hadn't a prayer above 15,000 feet. But one of the fastest prop planes in the air after the war was a P-39 with a P-38 engine. Curtiss requested both turbochargers and two stage two speed superchargers for the P-40, but to no avail.