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, a wheel arrangement associated with Nigel Gresley's P2 locomotives; Bulleid himself had worked with Gresley in the past. A second "Mikado" locomotive design was planned to have a Helmholtz pony truck – 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. Design Most of the detailed design for the Merchant Navy class was undertaken by the drawing office at Brighton works, but some work was also undertaken by Ashford and Eastleigh. This division of responsibility was possibly due to Bulleid's wish to restrict knowledge of the new class to a limited number of personnel. The design incorporated a number of novel features, compared to then-current steam locomotive practice in Great Britain. Cylinders, valve gear, wheels and brakes Three diameter cylinders drove the centre coupled axle. The inside cylinder was steeply inclined at 1:7.5 but the outside cylinders were horizontal. It was originally intended to use a gear-driven valve gear, but space restrictions within the frames and wartime material shortages led Bulleid to design his novel chain-driven valve gear. This component was unique amongst British locomotive design practices. It later gained a bad reputation, because it could cause highly irregular valve events, a problem compounded by the fast-moving Bulleid steam reverser. The entire system was located in a sealed oil bath, another unique design, providing constant lubrication to the moving parts. The locomotives were equipped with the unusual 6 ft 2 in (1.88 m) Bulleid Firth Brown (BFB) driving wheels which both lighter and