Bell P-39 Airacobra

Compromised from the start, this fighter found a unique niche

- Delwyn Mallett

DESPITE BEING largely derided by the US Army Air Corps and rejected as unsuitable by the RAF, the P-39 ended World War Two with the highest enemy kill tally of any US fighter.

In February 1937, recognising that its 'pursuit planes' were falling behind in development and were slower even than its own bombers, the United States Army Air Corps issued a directive for a new high-altitude interceptor. Power should come from the V-1710 Allison 28-litre supercharged V12 engine, with an additional General Electric turbocharger to endow it with high-altitude performance and a level flight speed of at least 360mph (marginally faster than the first Spitfire or Messerschmitt Bf 109.) Also specified was a tricycle undercarriage, then unusual in the fighter world, as well as a cannon as the main armament.

The recently established Bell Aircraft Corporation of Buffalo, New York (later famous for the Bell X-1, the first aircraft to break the sound barrier), submitted a radical proposal with a 'mid-engine' configuration. Rather than the 20mm cannon fitted to British and German fighters, the boys at Bell adopted a 'bigger is better' attitude and opted for the explosive stopping power of the massive Browning 37mm M4 cannon. And, because the Browning was a tad under 90in (2.27m) long, the only way to fit it into a single-engine fighter was to locate the engine behind the gun and the pilot.