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The Mitsubishi Ki-21 (or "Type 97 Heavy Bomber") (九七式重爆撃機 ''Kyūnana-shiki jūbakugekiki'') (Allied reporting name: "Sally" /"Gwen") was a Japanese bomber during World War II. It began operations during the Second Sino-Japanese War participating in the Nomonhan Incident, and in the first stages of the Pacific War, including the Malayan, Burmese, Dutch East Indies and New Guinea Campaigns. It was also used to attack targets as far-flung as western China, India and northern Australia. ==Design and development== In 1936, Imperial Japanese Army Air Service issued a requirement for a new heavy bomber to replace both the Ki-20 (Army Type 92 Heavy Bomber) and the Ki-1 (Army Type 93 Heavy Bomber). The design called for a crew of at least four, top speed of , endurance of at least five hours, and a bombload of . The design parameters were very ambitious, and few twin-engine bombers anywhere in the world could exceed such performance at that time. Both Mitsubishi and Nakajima were asked to build two prototypes each, a further proposal from Kawasaki being rejected. The Mitsubishi design was an all-metal mid-wing cantilever monoplane with retractable landing gear, ventral bomb bay and two radial engines. The first prototype flew on 18 December 1936, with the second prototype, which differed in replacing the dorsal turret of the first prototype with a long greenhouse canopy, following later in the month. In the resulting competition Mitsubishi's Ki-21 and Nakajima's Ki-19 were found to be similar, with the Ki-21 having better performance while the Nakajima design was a better bombing platform and had more reliable engines. In order to make a final decision, two further prototype were ordered from both Mitsubishi and Nakajima, with Mitsubishi instructed to change its own Mitsubishi Ha-6 radial engines for the Nakajima Ha-5 engines used by the Nakajima design and vice versa, while the Ki-21 gainied a revised glazed nose similar to that of the Ki-19 and revised tail surfaces. Thus modified, the Ki-21 proved superior, and was ordered into production as the "Army Type 97 Heavy Bomber Model 1A", being ordered into production in November 1937. Production aircraft began to enter service in August 1938, supplementing and then replacing the Fiat BR.20 bombers which had been purchased as an interim measure. Several improved versions followed (see below) before the production of the type ended in September 1944. A total of 2,064 aircraft were built, 1,713 by Mitsubishi and 351 by Nakajima. 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「Mitsubishi Ki-21」の詳細全文を読む スポンサード リンク
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