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BR Standard Class 6
The Standard class 6, otherwise known as the ''Clan'' Class, was a class of 4-6-2 ''Pacific'' tender steam locomotive designed by Robert Riddles for use by British Railways. Ten locomotives were constructed between 1951 and 1952, with a further 15 planned for construction. However, due to acute steel shortages in Britain, the order was continually postponed until it was finally cancelled on the publication of the 1955 Modernisation Plan for the re-equipment of British Railways.
The ''Clan'' Class was based upon the ''Britannia'' Class design, incorporating a smaller boiler and various weight-saving measures to increase the route availability of a ''Pacific''-type locomotive for its intended area of operations, the west of Scotland. The ''Clan'' Class received a mixed reception from crews, with those regularly operating the locomotives giving favourable reports as regards performance. However, trials in other areas of the British Railways network returned negative feedback, a common complaint being that difficulty in steaming the locomotive made it hard to adhere to timetables. Reports exist that suggest a degree of the disappointment with these locomotives was attributable to their being allocated to Class 7 work where they were only a Class 6 in reality; a problem put down to their very similar appearance to the BR Standard Class 7.
Some of the ''Clan'' Class locomotives took their names from the Highland Railway Clan Class which was being withdrawn from service at the time, indicating further their intended area of operations.〔 The class was ultimately deemed a failure by British Railways, and the last was withdrawn in 1966. None survived into preservation, although a project to build the next locomotive in line, number 72010 ''Hengist'', is progressing. The frame plates are presently at Riley & Son Ltd. at Bury awaiting further parts to commence assembly of the frame structure.
==Background==
Under the initial scheme for the creation of a series of British Railways standard locomotives, larger passenger and mixed traffic types were intended to be of the 4-6-2 ''Pacific'' wheel arrangement, the main advantage of which was that it could be fitted with a wide firebox capable of burning a range of coal types (and qualities). The ''Pacifics'' were originally intended to be produced in four power groups: 8, 7, 6, and 5, according to the system of power ratings inherited from the L.M.S. constituent company. Power groups 7, 6 & 5 were to be for mixed traffic (MT) service. The whole standardisation programme was launched with the building of the 7MT Britannia design in 1951; in the event, the 5MT proposal was dropped in favour of an updated version of the highly successful Stanier mixed traffic 4-6-0.〔Haresnape, Brian: ''Loco profile no. 12: BR Britannias'', p. 270〕 It was further appreciated that a ''Pacific'' of 6MT power could be built with a high enough route availability to fulfil all remaining requirements; this had been amply demonstrated by Oliver Bulleid, Chief Mechanical Engineer of the Southern Railway, who had developed a lighter version of his large 3-cylinder ''Merchant Navy'' Class in 1945. H.A.V. Bulleid, Oliver Bulleid's son, advocated that the resultant ''Light Pacifics'' had "almost 90%" route availability on the Southern railway network.〔Bulleid, H. A. V.: ''Bulleid of the Southern'', p. 68〕 The advantages of such a locomotive for use on some of the heavily restricted main lines in Scotland, such as the Dumfries to Stranraer line, had been further demonstrated by the remarkable performance of ''Light Pacific'' number 34004 ''Yeovil'' on the ex Highland Railway line to Inverness during the British Railways 1948 Locomotive Exchange Trials. During these trials the locomotive showed that a ''Light Pacific'' had the potential to revolutionise the timetable over this difficult trunk route. As the general policy of the Railway Executive was to eliminate as far as possible the perceived complication of multi-cylinder locomotives, an equivalent 2-cylinder ''Pacific'' was produced by mounting a smaller and lighter boiler on the standard 7MT chassis.〔Haresnape, Brian: ''Loco profile no. 12: BR Britannias'', p. 271〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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