Je m'étais posé cette question:
Pourquoi les avions américains pendant la seconde guerre mondiale ont si peu été équipés de canons type 20mm ou plus alors que les autres pays ont tous utilisés ce calibre plus ou moins massivement, ce calibre supérieur permettant des dégâts plus importants.
Les américains préférant multiplier le nombre de mitrailleuse de 12.7mm embarquées: 8 sur le P47, 12 fixes à l'avant du B25J...
Seuls les P38, P61, B29 et certaines versions du P39 et F4U ont été équipés de canons de 20mm.
Outre les qualités de la mitrailleuse M2 0.50 (12.7mm), une des meilleures mitrailleuses lourdes du conflit, ayant un calibre suffisant pour s'attaquer aux bombardiers mais aussi aux véhicules blindés légers, l'explication tient surtout au fait que la version du canon Hispano-Suiza HS404 de 20mm produite sous licence par les américains n'était pas fiable contrairement à la version produite et utilisé par les anglais...des fois ça tient à peu de choses...
Ci-dessous un extrait de wikipedia :
The British version was also licensed for use in the United States as the M1, with both the United States Army Air Corps (USAAC) and U.S. Navy planning to switch to the 20 mm caliber as soon as the gun could be produced in sufficient numbers. A very large building program was established, along with production of ammunition, in 1941. When delivered, the guns proved to be extremely unreliable and suffered a considerable number of misfires due to the round being lightly struck by the firing pin.[10] The British were interested in using this weapon to ease production in England, but after receiving the M1 they were disappointed. British wing-mounted fighter weapons by this period were cocked on the ground by the aircraft armourers before flight, the built-in pneumatic cocking mechanism used previously being regarded as unnecessary weight and detrimental to aircraft performance, so any stoppage in flight made the gun unusable until it could be cleared on the ground. The misfires also had the tendency to cause aircraft with wing-mounted guns to yaw towards the wing with the failed gun when the guns were fired, due to the unequal recoil, thus throwing-off the pilot's aim.
In April 1942 a copy of the British Mk.II was sent to the U.S. for comparison. The British version used a slightly shorter chamber and did not have the same problems as the U.S. version of the cannon.[10] The U.S. declined to modify the chamber of their version, but nonetheless made other modifications to create the unreliable M2. By late 1942 the USAAF had 40 million rounds of ammunition stored but the guns remained unsuitable. The U.S. Navy had been trying to go all-cannon throughout the war but the conversion never occurred. As late as December 1945 the Army's Chief of Ordnance was still attempting to complete additional changes to the design to allow it to enter service.[10] Some variations of the 20 mm guns used on the Lockheed P-38 Lightning aircraft were produced by International Harvester.[11] The P-38's nose-mounted M2 featured a built-in cocking system, and could simply be re-cocked in flight after a misfire, which made the misfires less of a problem than with other aircraft.[12]
The U.S. followed the British development closely and when the Mk.V was designed, the Americans followed suit with the A/N M3 but unreliability continued. After World War II the United States Air Force (USAF) adopted a version of the M3 cannon as the M24, similar in most respects except for the use of the addition of electrical cocking, allowing the gun to re-cock over a lightly struck round.[7] The problems of the American weapons led to most US fighters being equipped with the AN/M2 .50 cal Browning light-barrel HMG throughout the war.
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