Bell P-39 Airacobra

One of the most advanced American fighters at the start of World War II, the Bell P-39 Airacobra was still inferior to other Allied and Axis types by the beginning of American involvement in 1941.  Although not especially well-remembered in the United States as a dogfighter, the Russians put it to good use as a tank cracker.  Its heavy 37mm autocannon nose armament dictated that the engine be placed behind the pilot, with a long and heavy extension shaft driving the propeller.  This made room for the cannon to shoot through the propeller spinner.  Other notable features included nosewheel landing gear instead of the more conventional tailwheel type, as well as a side-opening car-style door instead of a sliding or hinged canopy.  In the opinions of many pilots, the Airacobra had only one major flaw:  It lacked a turbosupercharger, which severely limited its altitude performance.  Had Bell worked out the reliability issues, the Allied air forces may have found a superb high-performance air-to-air combat machine.