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The Type 99 Mark 1 cannon and Type 99 Mark 2 cannon were Japanese versions of the Oerlikon FF and Oerlikon FFL. They were adopted by the Imperial Japanese Navy in 1939 and served as their standard aircraft autocannon during World War II.〔http://www.lonesentry.com/ordnance/tag/cannon〕 ==Adoption== In 1935, officers in the Imperial Japanese Navy began to investigate 20 mm automatic cannon as armament for future fighter aircraft.〔Robert C. Mikesh, ''Zero'', Motorbooks USA, 1994.〕 Their attention was drawn to the family of aircraft autocannon manufactured by Oerlikon, the FF, FFL and FFS. These all shared the same operating principle, the advanced primer ignition blowback mechanism pioneered by the Becker cannon, but fired different ammunition: 20×72RB, 20×100RB, and 20×110RB, respectively. Following the import and evaluation of sample guns, the Imperial Japanese Navy decided in 1937 to adopt these weapons. To produce the Oerlikon guns, a group of retired Navy admirals created a new arms manufacturing company, the Dai Nihon Heiki KK. In 1939 this started producing a Japanese version of the FF, initially known as the Type E (because the Japanese transliteration of Oerlikon was ''Erikon'') but from late 1939 onwards formally known as the Type 99 Mark 1. A Japanese version of the FFL was produced as the Type 99 Mark 2.〔Anthony G. Williams and Emmanuel Gustin, ''Flying Guns World War II'', Airlife UK, 2003.〕〔Robert C. Mikesh, ''Japanese Aircraft Equipment'', Schiffer USA, 2004.〕 The FFS was tested, but not put in production. The 99 in the designation derived from the Japanese imperial calendar year, 1939 corresponding to the Japanese year 2599. The formal designations were Type 99 Mark 1 machine gun and Type 99 Mark 2 machine gun (Japanese: Kyū-Kyū Shiki Ichigō Kizyū, Kanji: 九九式一号機銃) and Kyū-Kyū Shiki Nigō Kizyū, Kanji: 九九式二号機銃). The Japanese Navy classified 20 mm weapons as machine guns rather than cannon.〔 These weapons were never used by the Japanese Army—there was almost no commonality in gun types or ammunition between Army and Navy. The Type 99 Mark 1 and Mark 2 were not models of the same gun, instead they had parallel lines of development into several different models. Because of the close technical similarity, several modifications were adopted to both guns simultaneously. Because it fired a bigger cartridge than the Type 99 Mark 1, the Type 99 Mark 2 had a higher muzzle velocity but a lower rate of fire, and was heavier. In the first years of the war the IJN preferred the Type 99 Mark 1, and it did not operationally use the Type 99 Mark 2 until 1942. Towards the end of the war it developed a preference for installing the Type 99 Mark 2, presumably to counter the improving performance and ruggedness of US combat aircraft. The Type 99 cannon suffered from relatively low muzzle velocity and rate of fire compared to other 20mm cannons but the trade off was an extremely light cannon that did not hinder flight performance of the IJN's fighter aircraft. The close economic and political ties between the IJN and Dai Nihon Heiki KK ensured that the latter had little competition. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Type 99 cannon」の詳細全文を読む スポンサード リンク
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