The Bell P-39 Airacobra was one of the primary American fighter aircraft in service when the United States entered World War II. Also used by the Soviet Air Force to devastating effect, the P-39 scored the highest number of individual kills attributed to any U.S. fighter type in the Eastern European theatre
Conceived as a single-engine high-altitude "interceptor" having "the tactical mission of interception and attack of hostile aircraft at high altitude, its lack of an efficient turbo-supercharger, preventing it from performing high-altitude interception. As such it was rejected by the RAF for use over western Europe but adopted by the USSR where most air combat took place at medium and lower altitudes.
Designed by the Bell Aircraft Corporation, the P-39had an unusual and innovative layout, with the engine installed in the centre fuselage, behind the pilot, and driving a tractor propeller via a long shaft. It was also the first fighter fitted with a tricycle undercarriage.
The main reason for the unusual positioning of the P-39’s Allison V-1710 liquid-cooled V-12 engine behind the cockpit was to free up space for the heavy main armament, a 37mm Oldsmobile T9 cannon firing through the centre of the propeller hub for optimum accuracy and stability when firing.
A secondary benefit of the mid-engine arrangement was that it created a smooth and streamlined nose profile. Much was made of the fact that this resulted in a configuration “with as trim and clean a fuselage nose as the snout of a high velocity bullet”. Entry to the cockpit was through side doors (mounted on both sides of the cockpit) rather than a sliding canopy. Its unusual engine location and the long drive shaft caused some concern to pilots at first, but experience showed this was no more of a hazard in a crash landing than with an engine located forward of the cockpit.
Whilst most fighter aircraft design was based around specific mission performance, the P-39 was the first aircraft to be designed around a weapons system - the 37mm Oldsmobile T9 cannon which fired a 1.3 lb projectile capable of piercing 2 cm of armour at 450 m with armour-piercing rounds. Due to its size and weight, it was impossible to mount the cannon on the wingtips so the engine was moved back behind the cockpit leaving the nose section to house the weapon.
The tractor propeller was driven via a 3m long drive shaft made in two sections, incorporating a self-aligning bearing to accommodate fuselage deflection during violent manoeuvres. This shaft ran through a tunnel in the cockpit floor and was connected to a gearbox in the nose of the fuselage which, in turn, drove the three - or (later) four-bladed propeller via a short central shaft.
The Airacobra saw combat throughout the world, particularly in the Southwest Pacific, Mediterranean and Soviet theatres with the most successful and numerous use of the P-39 by the Red Air Force.
Receiving the considerably improved N and Q models via the Alaska-Siberia ferry route, the tactical environment of the Eastern Front did not demand the high-altitude performance the RAF and USAAF did. The comparatively low-speed, low-altitude nature of most air combat on the Soviet Front suited the P-39's strengths: sturdy construction, reliable radio gear, and significant firepower.
The first Soviet Airacobras had a 20 mm Hispano-Suiza cannon and two heavy Browning machine guns, synchronised and mounted in the nose. Later, Cobras arrived with the M4 37 mm cannon and four machine guns, two synchronised and two wing-mounted.
Soviet pilot Nikolai G. Golodnikov, recalling his experiences of the P-39 said "We immediately removed the wing machine guns, leaving one cannon and two machine guns," That modification improved roll rate by reducing rotational inertia. Soviet airmen appreciated the M4 cannon with its powerful rounds and the reliable action but complained about the low rate of fire (three rounds per second) and inadequate ammunition storage (only 30 rounds).
The last plane shot down by the Luftwaffe was a Soviet P-39, with the last Soviet air victory was in a P-39 on May 9 when Kapitan Vasily Pshenichikov scored against a Focke-Wulf Fw 189, in the sky over Prague. Five of the 10 highest scoring Soviets aces logged the majority of their kills in P-39s. Pokryshkin scored 47 of his 59 victories in P-39s, making him the highest scoring P-39 fighter pilot of any nation, and the highest scoring Allied fighter pilot using an American fighter.
23 reconditioned Airacobras were also loaned to the RAAF as a stop-gap measure during the opening months of the Pacific War when the Australian’s were only able to obtain enough Curtiss Kittyhawks to equip 3 squadrons destined for front line duties in Papua New Guinea. Eventually the RAAF were able to secure the upgraded Spitfire for home defence duties.
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