BR Standard Class 6 - Background

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. 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. 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.