SR Merchant Navy Class - Background

Background

The Southern Railway was the most financially successful of the "Big Four", but this was largely based on investment in suburban and main line electrification . After the successful introduction of the SR Schools class in 1930 the railway had lagged behind the others in terms of modernising its aging fleet of steam locomotives. Following the retirement of the General Manager of the Southern Railway Sir Herbert Walker and Richard Maunsell the Chief Mechanical Engineer (CME) in 1937, their successors considered that the time had come to change this situation. In March 1938 the new General Manager Gilbert Szlumper authorised Oliver Bulleid, Maunsell's replacement, to prepare designs for twenty express passenger locomotives. The deteriorating international situation prior to the Second World War was an additional factor in this decision.

Bulleid's first suggestion was for an eight-coupled locomotive with a 4-8-2 wheel arrangement for the heavily loaded Golden Arrow and Night Ferry Continental express trains, although this was quickly modified to a 2-8-2 equipped with a Helmholtz "Bissel bogie" – a system already successfully applied on the Continent. However, both proposals for eight-coupled locomotives were resisted by the Southern Railway's Chief Civil Engineer, so a new 4-6-2 Pacific design was settled upon instead. The new design was intended for express passenger and semi-fast work in Southern England, though it had to be equally adept at freight workings due to the nominal "mixed traffic" classification Bulleid applied to the class for them to be built during wartime. Administrative measures had been put in place by the wartime government preventing the construction of express passenger locomotives due to shortages of materials and a need for locomotives with freight-hauling capabilities. Classifying a design as "mixed traffic" neatly circumvented this restriction.