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SR Merchant Navy class
The SR Merchant Navy class (originally known as the 21C1 class, and later informally known as Bulleid Pacifics, Spam Cans – which name was also applied to the Light Pacifics – or Packets) is a class of air-smoothed 4-6-2 (Pacific) steam locomotives designed for the Southern Railway by Oliver Bulleid. The Pacific design was chosen in preference to several others proposed by Bulleid. The first members of the class were constructed during the Second World War, and the last of the 30 locomotives in 1949.
Incorporating a number of new developments in British steam locomotive technology, the design of the Merchant Navy class was among the first to use welding in the construction process; this enabled easier fabrication of components during the austerity of the war and post-war economies. In addition, the locomotives featured thermic syphons in their boilers and the controversial Bulleid chain-driven valve gear. The engines were named after the Merchant Navy shipping lines involved in the Battle of the Atlantic, and latterly those which used Southampton Docks: a publicity move by the Southern Railway, which operated the docks at the time.
Due to problems with some of the more novel features of Bulleid's design, all members of the class were modified by British Railways during the late 1950s, losing their air-smoothed casings in the process. The Merchant Navy class operated until the end of Southern steam in July, 1967. A third of the class has survived and can be seen on heritage railways throughout Great Britain. They were known for reaching speeds of up to 105 mph (167 km/h); such speeds were recorded by examples including No. 35003 Royal Mail (since scrapped) and Nos. 35005 Canadian Pacific and 35028 Clan Line (both preserved).
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 ageing 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 20 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, 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 into 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.
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.
Three 18 inches (46 cm) diameter cylinders drove the centre coupled axle. The inside cylinder was steeply inclined at 1:7.5, but the outside cylinders were all 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.
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SR Merchant Navy class
The SR Merchant Navy class (originally known as the 21C1 class, and later informally known as Bulleid Pacifics, Spam Cans – which name was also applied to the Light Pacifics – or Packets) is a class of air-smoothed 4-6-2 (Pacific) steam locomotives designed for the Southern Railway by Oliver Bulleid. The Pacific design was chosen in preference to several others proposed by Bulleid. The first members of the class were constructed during the Second World War, and the last of the 30 locomotives in 1949.
Incorporating a number of new developments in British steam locomotive technology, the design of the Merchant Navy class was among the first to use welding in the construction process; this enabled easier fabrication of components during the austerity of the war and post-war economies. In addition, the locomotives featured thermic syphons in their boilers and the controversial Bulleid chain-driven valve gear. The engines were named after the Merchant Navy shipping lines involved in the Battle of the Atlantic, and latterly those which used Southampton Docks: a publicity move by the Southern Railway, which operated the docks at the time.
Due to problems with some of the more novel features of Bulleid's design, all members of the class were modified by British Railways during the late 1950s, losing their air-smoothed casings in the process. The Merchant Navy class operated until the end of Southern steam in July, 1967. A third of the class has survived and can be seen on heritage railways throughout Great Britain. They were known for reaching speeds of up to 105 mph (167 km/h); such speeds were recorded by examples including No. 35003 Royal Mail (since scrapped) and Nos. 35005 Canadian Pacific and 35028 Clan Line (both preserved).
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 ageing 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 20 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, 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 into 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.
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.
Three 18 inches (46 cm) diameter cylinders drove the centre coupled axle. The inside cylinder was steeply inclined at 1:7.5, but the outside cylinders were all 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.