Merchant Navy Class

4-6-2

Design & Appearance

Inside and out, the new engines were full of novelties, included to improve the availability of the steam locomotive. Conversely, however, many of these new features were detrimental. Over the years, many commentators have suggested that given the SR was an apologist to electric traction, combined with the intervening war years, Bulleid was forced to innovate quickly. Of his MN Class, the most prominent external feature was the ‘’air-smoothed casing’’, which fully enclosed the boiler and was carried on the engine’s main frame. The reasons cited for the inclusion of such casing are numerous, although it is generally accepted that it allowed the engines to be cleaned simply by passing through an automatic carriage washer. In addition, it gave the steam locomotive a modern and revolutionary appearance, a welcomed up-to-date image as electric traction gradually took a hold of the SR network. The casing also concealed external boiler fittings and pipes, which meant a more relaxed approach could be taken towards the location of these components, for they would not spoil the overall aesthetics. Plenty of space within the casing existed for boiler expansion, and the latter itself was copiously lagged with fibreglass. The tapered boiler comprised 164 individual tubes, and was of welded construction, which reduced construction time. The air-smoothed lines of the engine were continued behind on a tender of 5000-gallon water capacity; the maximum coal load was 5-tons.

A new form of ‘’Boxpox’’ wheel was produced for the MN Class, favoured over the more conventional spoked wheel. This was devised jointly by Bulleid and Sheffield Steel Maker ‘’Firth Brown’’, the wheel type thus becoming known as ‘’Bulleid-Firth-Brown’’. The wheels were constructed by bridging together individual plates of steel, and overall they were 10% lighter than the equivalent spoked wheels. In addition, this was a stronger disc design which provided a more uniform support to the tyre. Conventional spoked wheel centres were more prone to distortion (leading to loose tyres) and cracking. Reciprocating balance weights within the driving wheels were dispensed with, in an attempt to tackle the ‘’hammer blow’’ effect on the track. In brief, these weights were part of a balancing mechanism used in locomotives to reduce the vibrations caused by the pistons. Furthermore, ‘’hammer blow’’ is the maximum vertical unbalanced force imposed upon the track by an engine’s driving wheels. Generally, the greater the ‘’hammer blow’’ effect, the more damage is potentially sustained by the track.

The trio of cylinders within the MN Class were of 18-inch diameter; two were externally located, whilst the third was positioned within the locomotive, suspended above the rear of the front bogie. All three were driven by separate valve gear, linked to the middle coupled axle by a series of chains running through a 40-gallon capacity 2-inch-deep oil bath. Yet another Bulleid innovation, a number of advantages were attached to this internal chain-driven system. Firstly, moving parts were now protected from the build-up of dirt associated with those engines comprising conventional outside valve gear. Secondly, running this system through an oil bath meant that other moving parts within the engine, which would otherwise have been relatively inaccessible, could be lubricated automatically. This was achieved by installing a series of reversible pumps within the bath, which distributed the oil around the locomotive through a network of pipes. Finally, the new arrangement also meant that patents associated with the more mainstream Walschaerts’ valve gear could be avoided. Ultimately aimed at reducing day-to-day maintenance, faults soon emerged from this rather untried novelty which, conversely, made the locomotives expensive to run. Metal sheets of varying thickness were welded together to produce a stiff oil bath which, with little flexibility, was prone to cracking. The chain-driven valve gear was indeed a clever concept, but it was also the result of building a locomotive during wartime. The original plan was to employ a propeller shaft system incorporating gears, but materials and components for this had become difficult to obtain.

Nationalisation

Under the Southern Railway, two MN batches were completed, a total of twenty engines. The final two locomotives, Nos. 21C19 and 21C20 (latterly named ‘’French Line C.G.T and ‘’Bibby Line’’ respectively), were deployed into service in June 1945, but already the days were numbered for the fleet. In November 1946, the war now over, the SR Board announced a £15 million (about £464,000,000 at 2008 prices) modernisation of those lines east of Portsmouth. All were to be converted to electric or diesel-electric operation. The Eastern Section main lines to Ramsgate and Dover via both Faversham and Tonbridge were to be electrified, and the Medway Valley and Hastings lines similarly treated. Haulage of heavy boat trains from Victoria, for which the MN Class had been specifically procured, would be undertaken by electric locomotives. Completion of the scheme was expected to occur in 1955, and steam would be completely eliminated from Central and Eastern Sections of the SR. At this time, the railways were still under Government Wartime Control, and the prospect of nationalisation loomed, vehemently opposed by Bulleid. ‘’British Railways’’ formally came into existence on 1st January 1948, and Bulleid was now able to enjoy little of the autocratic power he once had at the SR. In the following year, he left for Dublin, where he became Consulting Mechanical Engineer for Coras Iompair Eireann (Irish National Railways) – the third batch of ten MN Pacifics had not yet been fully completed.

Being commissioned to traffic under BR auspices, the last ten MN engines were never numbered in the Bulleid series. Instead, they received more conventional BR numbers from the outset. The first of the BR batch was No. 35021 ‘’New Zealand Line’’, which entered traffic in September 1948 and formally received its name on 24th of the following month. Over the three batches, tender water capacities varied: Nos 21C1 to 21C10 (Nos. 35001 to 35010) were coupled to 5000-gallon tenders; Nos. 21C11 to 21C20 (Nos. 35011 to 35020) had 5100 gallon tenders; and finally, Nos. 35021 to 35030 were eventually equipped with 6000-gallon tenders. Tenders for the first two batches were built at Ashford, whilst those for the last ten engines were Brighton-built. With reference to the latter, many were completed later than the locomotives, thus these engines initially ran with 5500-gallon tenders built for the Light Pacifics (more of later). Furthermore, the 6000-gallon tenders did not stay their entire careers with their intended engines. The trend of increasing tender capacity was set to continue when consideration was given to producing an eight-wheel 8000-gallon variant, but nothing ever came of this idea. The third batch of ten MN engines were fitted with TIA (Traitement Integral Armand) water treatment equipment, first used on the continent by SNCF. In brief, this involved feeding a mixture of carbonate of soda, phosphate of soda, caustic soda, and tannin into the water supply by means of a distributor. This aimed to purify the water, therefore increasing heat efficiency and slowing down boiler corrosion. As a result, it was hoped that maintenance costs would fall.

MN engines had a tare of 84 tons 14 cwt, which barred them from numerous secondary routes on the SR system where they were deemed too heavy. For those lines where the MN Class were out of gauge, particularly the ‘’Withered Arm’’ west of Exeter, a lighter and, ultimately, more numerous breed of ‘’Light Pacific’’ was produced. This type eventually totalled 110 engines and was literally a scaled-down Merchant Navy. A reduced tare of 77 tons gave these engines, dubbed ‘’Lightweights’’, a much wider route availability, and more details concerning this type can be found in the Bulleid Light Pacific section.

Mention should also be made of the 1948 Locomotive Exchange Trials, a prelude to the design and production of what later became the ‘’BR Standard Engines’’. The trials were designed to take the main line express locomotives of the erstwhile ‘’Big Four’’ railway companies, and run them on foreign territory, to see how they fared. For instance, ex-LMS and ex-LNER engines were run on the metals of the former GWR and SR companies, and the reverse was also true. Through this process, the best design characteristics of each major Grouping design could be identified and incorporated into the proposed range of BR Standard Classes. Three MN engines, Nos. 35017 ‘’Belgian Marine’’, 35019 ‘’French Line CGT’’, and 35020 ‘’Bibby Line’’, were equipped with ex-LMS Stanier tenders for the exchanges. These tenders featured water pick-up apparatus for use on those BR Regions that featured water troughs. In addition, No. 35020 was fitted with extra long smoke deflectors but, as it transpired, this engine was subsequently not used in the trials. Ex-LMS Stanier Pacifics which came to the SR were paired with ‘’Austerity’’ eight-wheel tenders, which featured a large water capacity to compensate for the lack of troughs. During this year, the MN engines received a ‘’7P’’ power classification (‘’P’’ for ‘’Passenger’’). This was revised to ‘’8P’’ in January 1951.

On 24th April 1953, No. 35020 was fronting the 4:30 PM Exeter Central to Waterloo service when its driving axle fractured. Running at an estimated 70 MPH through Crewkerne station, the locomotive shed a brake block, which subsequently flew into one of the canopy stanchions on the ‘’up’’ side platform. The canopy partially collapsed, but fortunately no injuries on the platforms or within the train were sustained. Indeed, the carriages remained completed on the rails, and only the centre driving wheels of the engine were derailed. As a result, the entire thirty-strong MN Class was removed from service, to permit inspection of all members for similar faults. To deputise for the class, a fleet of engines comprising ‘’Britannias’’, ex-LMS Class Fives, ex-LNER ‘’V2s’’ and ‘’B1s’’, were despatched to both South Western and South Eastern Divisions of the Southern Region.
 

21C14/35014: Nederland Line

On the ''home run'', No. 35014 is seen passing through Vauxhall with an express from Bournemouth in November

1966. In typical grimy condition for the period, this locomotive remained in service until March 1967. Subsequently

towed to the scrap yards of South Wales, it was cut up in Newport in September of the same year. It had a career

of over two decades, having entered traffic with the SR in February 1945. The engine had existed in its rebuilt

form since July 1956. © David Glasspool Collection

21C17/35017: Belgian Marine

It is 23rd May 1965 and No. 35017 ''Belgian Marine'' has just taken over from No. 34051 ''Winston Churchill''

at Salisbury on a Stephenson Locomotive Society rail tour. This had come in from Birmingham Snow Hill via

Oxford, Basingstoke, and Andover. No. 35017 took the train onwards to Exeter St David's, and then up to

Westbury via the ex-GWR main line. No. 35017 remained in service until July 1966, and within two months

was scrapped in Newport, South Wales. It had begun life in April 1945 as No. 21C17, and was latterly rebuilt

by BR in March 1957. © David Glasspool Collection

35021: New Zealand Line

With eight carriages (two of which are BR Mk 1 Full Brakes) and a parcels van in tow, No. 35021 is seen on the

approaches to Weymouth on 27th August 1959. The engine had been in its rebuilt form for just two months,

having re-emerged from Eastleigh Works in its new form during the previous June. A nine-vehicle loading

would have been light for a Merchant Navy: much of the very heavy traffic, for which they had originally

been built, never materialised. No. 35021 was the first of the BR-built batch, entering traffic in September

1948, thus it did not receive a Bulleid number. It also went straight to Malachite Green livery when new,

this being replaced two years later by the attractive Experimental Blue scheme. BR Lined Green was the

order of the day in February 1952, a scheme the engine wore in both original and rebuilt forms until the

end. No. 35021 was one of the earlier Merchant Navy withdrawals, being taken out of service in August

1965. It was despatched to Swansea, South Wales, for scrapping, and had been reduced to bits within

two months. © David Glasspool Collection

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