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|boilerpressure = |cylindercount = Three |cylindersize = |tractiveeffort = |operator = |operatorclass = SECR / SR: N1 |powerclass = BR: 4P5FB |withdrawndate = 1962 |disposition = All scrapped }} The SECR N1 class was a type of 3-cylinder 2-6-0 ('mogul') steam locomotive designed by Richard Maunsell for mixed traffic duties, initially on the South Eastern and Chatham Railway (SECR), and later operated for the Southern Railway (SR). The N1 was a development of the basic principles established by the Great Western Railway's (GWR) Chief Mechanical Engineer (CME) George Jackson Churchward and by Maunsell's previous N class design.〔Scott-Morgan (2002), p. 18〕 The N1 prototype was the result of modifications made to N class No. 822 during construction in 1922. The locomotive became operational in 1923 and used parts interchangeable with other Maunsell locomotive classes. The prototype N1 was the only member of the class constructed before the SECR became part of the Southern Railway at the Grouping in 1923, and featured a variant of the Gresley conjugated valve gear designed by Harold Holcroft. The class set the precedent for the Southern Railway's subsequent 3-cylinder designs. The N1s compared favourably with the N class, although the type showed little improvement in performance. More of the class were built when it became clear that the type's smaller cylinders provided greater route availability.〔 A total of six engines were built. The N1 class was primarily used on the Eastern section of the Southern Railway network, and used by the Southern Region of British Railways (BR) from 1948. The N1s gave valuable service until they were withdrawn in 1962. None were preserved. == Background == Richard Maunsell's N class mixed-traffic 2-6-0 prototype for the South Eastern and Chatham Railway (SECR) was completed in 1917.〔 It showed a marked improvement in performance over his predecessor Harry Wainwright's 0-6-0 and 4-4-0 designs when tested on freight and local passenger trains.〔 The success of the prototype encouraged the SECR management to order a batch of 15 in 1919 after government restrictions regulating locomotive production during the First World War were relaxed.〔 Ashford locomotive works was already committed to undertaking deferred repair work however, which temporarily slowed construction of new locomotives.〔 This resulted in the gradual completion of the 1919 N class order as works capacity permitted between 1920 and 1923.〔 Operational experience with the N class prototype demonstrated that it was capable of coping with peacetime passenger and freight traffic on the mainline between London and Ramsgate, but Maunsell anticipated an increase in traffic that would require a more powerful locomotive capable of hauling longer trains. The use of larger engines was prevented by low permitted axle loadings on parts of the SECR network,〔 caused by economies in track construction by using flint beach pebbles as track ballast; this material failed to hold the track in place when under strain and could not support heavy locomotives.〔Bradley (1961), p. 47〕 In the meantime Maunsell settled upon producing a 3-cylinder version of the N class 2-6-0, which provided the opportunity to test a variant of the Gresley conjugated valve gear developed by his assistant, Harold Holcroft.〔 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「SECR N1 class」の詳細全文を読む スポンサード リンク
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