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The North American B-25 Mitchell is an American twin-engine, medium bomber manufactured by North American Aviation. It was named in honor of Major General William "Billy" Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in every theater of World War II and after the war ended many remained in service, operating across four decades. Produced in numerous variants, nearly 10,000 Mitchells rolled from NAA factories.〔 These included a few limited models, such as the United States Marine Corps' PBJ-1 patrol bomber and the United States Army Air Forces' F-10 reconnaissance aircraft and AT-24 trainers. ==Design and development== The Air Corps issued a circular (Number 38-385) in March 1938 describing the performance they required from the next bombers — a payload of with a range of at more than .〔Baugher, Joe. ("North American NA-40." ) ''American Military Aircraft: US Bomber Aircraft'', 6 March 2000. Retrieved: 24 May 2015.〕 Those performance specifications led NAA to submit their NA-40 design. The NA-40 had benefited from the North American XB-21 (NA-39) of 1936 which was the company's partly-successful design for an earlier medium bomber that had been initially accepted and ordered but then cancelled. However, the company's experience from the XB-21 contributed to the design and development of the NA-40. The single NA-40 built flew first at the end of January 1939. It went through several modifications to correct problems. These improvements included fitting 1,600 hp Wright R-2600 "Double Cyclone" radial engines, in March 1939 which solved the lack of power.〔 In March 1939, North American delivered the substantially redesigned and improved NA-40 (as NA-40B) to the United States Army Air Corps for evaluation.〔 It was in competition with other manufacturers' designs (Douglas 7B, Stearman X-100, and the Martin Model 167F)〔Baugher, Joe. ("Douglas Model 7B." ) ''American Military Aircraft: US Bomber Aircraft'', 2000. Retrieved: 28 May 2015.〕 but failed to win orders. The aircraft was originally intended to be an attack bomber for export to the United Kingdom and France, both of which had a pressing requirement for such aircraft in the early stages of World War II. However, the French had already opted for a revised Douglas 7B (as the DB-7). Unfortunately, the NA-40B was destroyed in a crash on 11 April 1939 while undergoing testing. Although the crash was not considered due to a fault with the aircraft design, the Army ordered the DB-7 as the A-20. The Air Corps issued a specification for a medium bomber in March 1939: over at 〔Baugher, Joe. ("North American B-25 Mitchell." ) ''American Military Aircraft: US Bomber Aircraft'', 6 March 2000. Retrieved: 24 May 2015.〕 NAA used the NA-40B design to develop the NA-62 which competed for the medium bomber contract. There was no YB-25 for prototype service tests. In September 1939, the Air Corps ordered the NA-62 into production as the B-25, along with the other new Air Corps medium bomber, the Martin B-26 Marauder "off the drawing board". The NA-40 lost out to the Douglas A-20 in the attack type competition, but NAA developed a more advanced design, the NA-40B, which in turn led to the NA-62, B-25 Mitchell bomber.〔Parker 2013, pp. 77-79, 83, 88, 92.〕〔Borth 1945, pp. 70, 92, 244.〕 Early into B-25 production, NAA incorporated a significant redesign to the wing dihedral. The first nine aircraft had a constant-dihedral, meaning the wing had a consistent, upward angle from the fuselage to the wingtip. This design caused stability problems. A slight anhedral on the outboard wing sections nullified the problem and gave the B-25 its gull wing configuration.〔Chorlton ''Aeroplane'' May 2013, p. 74.〕 Less noticeable changes during this period included an increase in the size of the tail fins and a decrease in their inward cant. NAA continued design and development in 1940 and 1941. Both the B-25A and B-25B series entered AAF service. The B-25B was operational in 1942. Combat requirements lead to further developments. Before the year was over, NAA was producing the B-25C and B-25D series at different plants. Also in 1942, the manufacturer began design work on the cannon-armed B-25G series. The NA-100 of 1943 and 1944 was an interim armament development at the Kansas City complex known as the B-25D2. Similar armament upgrades by U.S-based commercial modification centers involved about half of the B-25G series. Further development led to the B-25H, B-25J and B-25J2. The gunship design concept dates to late 1942 and NAA sent a field technical representative to the SWPA. The factory produced B-25G entered production during the NA-96 order followed by the redesigned B-25H gunship. The B-25J reverted to the bomber role, but it, too, could be outfitted as a strafer (pictured above). North American Aviation manufactured the greatest number of aircraft in World War II. It was the first time a company had produced trainers, bombers and fighters simultaneously (the AT-6/SNJ Texan, B-25 Mitchell, and the P-51 Mustang). It produced B-25s at both its Inglewood main plant and an additional 6,608 aircraft at its Kansas City, Kansas plant at Fairfax Airport.〔〔〔Herman 2012, pp. 11, 88, 115, 140-143, 263, 297.〕 Postwar, the USAF placed a contract for the TB-25L trainer in 1952. This was a modification program by Hayes of Birmingham, Alabama. Its primary role was reciprocal engine pilot training. A development of the B-25 was the North American XB-28, designed as a high-altitude bomber. Two prototypes were built with the second prototype, the XB-28A, evaluated as a photo-reconnaissance platform but the aircraft did not enter production.〔Norton 2012, p. 68.〕 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「North American B-25 Mitchell」の詳細全文を読む スポンサード リンク
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