The Merchant Navy pacifics: innovation ahead of their time

Article by Ian Crowder in 2005 (with minor updates)


The visit of SR Merchant Navy class pacific no. 35005 Canadian Pacific for the September 2005 steam gala weekend offered a tantalising glimpse of what is to be on the Honeybourne Line when sister locomotive, no. 35006 Peninsular & Oriental SN Co enters service after its long and thorough overhaul at Toddington. As of April 2010, No. 35006 is looking increasingly complete as the weeks progress, following return of the fully steam-tested boiler from Chatham to Toddington and re-assembly of the locomotive progressing well.  P&O returned to service in May 2016.  


35005 Canadian Pacific is owned by the Mid Hants 'Watercress' Line (where it is pictured, courtesy of Tony Wood the Mid Hants' webmaster). We're grateful to Colin Chambers at Alresford station for helping us with the arrangements for the engine to pay this visit.


This was the first visit by a working member of the class to the GWR. It made a star appearance just for the GWR's Gala over the weekend of 10th and 11th September 2005, but returned for a more extended visit the following year. Indeed, the old Stratford to Cheltenham route was well out of bounds for these class 8 locomotives - it is believed (unless someone can comment otherwise) that no. 35028 'Clan Line' is the only Merchant Navy to have run over the route, when heading south in a locomotive movement shortly before the line was closed.


'Space age' technology for the Southern

It's hard to imagine how people might have reacted when they saw the first member of the class emerge from Eastleigh works in 1941. 'Sensation' is probably an understatement - the locomotives were anything but conventional in appearance and engineering innovation. The Southern Railway's Chief Mechanical Engineer, O V S Bulleid, came from London & North Eastern Railway and although influenced by LNER practice, was probably far ahead of his time.


Three batches of 10 were completed, the last being delivered by British Railways following nationalisation.


The 30 Merchant Navy's were a three-cylinder design with a boiler featuring a wide firebox - but that's about as far as LNER comparisons go. Behind the unconventional 'air-smoothed' casing (possibly influenced by Gresley's semi -streamlined P2 class 2-8-2's) and American 'Boxpok' style wheels were a host of ideas never tried before. Not least of these was chain driven valve gear between the frames, the valve gear and middle motion totally enclosed in an oil bath, intended to eliminate the need for staff to get between the frames to 'oil up'. A steam reverser operated the valve gear and the whole assembly completely eliminated the hammer-blow associated with conventional locomotives. Another major innovation included an all-steel boiler equipped with thermic siphons within the firebox to promote better water circulation, and working at an unprecedented 280lb/ Rocking grate and hopper ashpan made for quick and clean disposal while the cab layout was ergonomically designed to simplify operation, this including steam-operated firehole doors worked by a treadle. An electric generator powered lighting for cab, gauges, inspection lights and head and tail train code lights.


The decision was taken to name the class after shipping companies serving Southampton Docks - an inspired choice that highlighted the SR's connections with the continent and international travel - even if it meant some extremely long names (such at 35006: Peninsular & Oriental Steam Navigation Co to give it its full name!).


Change for the better?

Although the Merchant Navy class (and the similar but smaller West country and Battle of Britain classes) proved fast, free running and powerful they were beset with a host of irksome maintenance problems. For example, the oil bath proved impossible to keep oil tight; the chains were prone to stretching and the steam reverser approximate. The air -smoothed casing, while easy to keep clean (the engines were designed to go through carriage washers) proved a nightmare for access when things went wrong. They spent much more time in the works than they should. However, the boiler was a triumph - it was free steaming and, if a little heavy on coal, would deliver whatever the driver demanded of it - provided the fireman could keep up! The class routinely ran at speeds well in excess of 80mph, 100mph not being uncommon.


In 1955, the British Railways Board gave authority for the first 15 members of the class to be rebuilt to more conventional design and the first, no. 35018, emerged later that year. The influence of Riddles (designer of the British Railways standard designs, including the 9F class 2-10-0) was clear and an obvious comparison was made with the BR 'Britannia' pacifics.


Gone was the air-smoothed casing and chain driven valve gear, replaced with three separate sets of Walschearts gear. Gone too, was the troublesome steam reverser. A new smokebox was fitted (but retaining the distinctive oval Bullied smokebox door); and an additional smokebox saddle fitted to strengthen the frames. A new superheater feeder and outside steam pipes were provided along with new pistons, piston rods and cylinder drain cocks. New mechanical lubricators were fitted, along with a new regulator and ashpan design. Finally, weights had to be fitted to the wheels to counteract the hammer-blow produced by the motion.


Success of the rebuild was such that all members of the class were rebuilt by 1959 and similar work immediately started on the 110 light pacifics. Although the rebuilt locomotives were expected to remain in service until 1987, the modernisation plan put paid to that - and like Riddles' Standard classes, had lamentably short lives. Nevertheless, the Merchant Navy's put in commendable and reliable performance with little, if any, loss in performance. Indeed, there are several authenticated examples of the rebuilt locomotive exceeding the magic 'ton' - no. 35003 'Royal Mail' topping 106mph with a Weymouth-Waterloo service between Basingstoke and Woking, just two weeks before the end of SR steam.


The SR was the last main line in the UK to operate express services with steam: the Waterloo - Southampton - Bournemouth - Weymouth expresses remaining almost exclusively Bulleid-pacific hauled right to the end. Appropriately, it fell to the last member of the class, 35030 'Elder-Dempster Lines' to haul the very last steam-hauled train to Waterloo: the 14.11 Weymouth-Waterloo on 9 July 1967. The next day, modern traction took over and there was not a breath of steam left to be seen. A sad day indeed and seemingly, the last rites of a remarkable class of locomotive had been performed.


Fortunately, 11 members of the class (just over a third of the total!) survived the cutter's torch and 35028 and 35005 have, for example, over recent years put in sterling performances on tour duty. Other members of the class are close to completion after long and expensive restorations ,so we may enjoy seeing these fine locomotives in action for many years to come - and not least of them our own resident 35006 which is now a regular performer on our line.