But then the Allison finally turned into a great engine. It was an attempt to go to high technology, and the war demanded it be put into service before it was fully developed. Those lousy performing aircraft with early Allisons were dogs at high altitude because they lacked the originally intended turbocharger.
A bit of history on that. By the mid thirties the performance of fighter aircraft had evolved so that a single stage supercharger was inadequate. But with two-stage chargers there was a real problem overboosting the engine at low altitude. So controls were added so that pilot could manage boost pressure. However, if pilot got into a dogfight, especially one that involved changes of altitude, that was just one more task for a very busy pilot. The original Allison concept included a fixed speed primary blower and an automatically (pneumatically) controlled turbocharger. Development of that turbocharger with constant boost pressure took awhile, so initial engines just did away with second charger and were intended for low altitude use. Eventually it became a good fighter engine and the turbocharger worked as planned.