The Bell P-39 Airacobra originally flew with excellent performance but by the time the aircraft reached the front lines the Army Air Corp had changed so many features that the plane was far from what Bell had originally designed. They added weight, removed the supercharger from the Allison engine that didn't have the power it claimed. What could have been and should have been one of the best aircraft of WWII turned out to be much less. Even with all its flaws they still produced 9,584 P-39s.