MN 4-6-2 SR Bulleid Merchant Navy 35001 – 35030


Power Classification 7P reclassified 8P in 1951
Introduced 1941 – 1949
Designer Bulleid
Company SR
Weight – Loco 94t 15cwt – Rebuilt locomotives 97t 18cwt
               Tender 5,000 gallon – 47t 16cwt

5,100 gallon – 49t 7cwt

6,000 gallon – 52t 7cwt

Driving Wheels 6ft 2ins
Boiler Pressure 280psi superheated – Later reduced to 250psi
Cylinders Three – 18in x 24in
Tractive Effort 37,515lbf  – Later reduced to 33,495lbf
Valve Gear Bullied (piston valve)

Rebuilt locomotives Walschaert (piston valves)

The Chairman of the Southern board, Robert Holland-Martin was very aware of the prestige being earned by the LMS with their Coronation Locos, and the LNER with the A4. The Southern Railway was the most financially successful of the Big Four railway companies (GWR, LMS, LNER & SR), 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.

In 1937, Maunsell announced his retirement as he was 65 and was suffering from ill-health and Bulleid was invited to apply for the job as CME for the Southern. Bulleid had been Gresley’s right hand man since the GNR days, and at 54 years old had more than years to serve before retirement.

As the only candidate Bulleid got the job, and took up the post at Waterloo in 1937. He was the only candidate because he was approached by the Southern Railway General Manager (Sir Herbert Walker) who asked Bullied to apply for the post. Bullied at that time was working for the LNER as assistant to Gresley and was quite content with his role. Sir Herbert Walker told Bullied to consult with the Chief General Manager (Sir Ralph Wedgwood) of the LNER who told Bullied that the job with the Southern Railway was his.

Although not directly responsible for the design of a locomotives he had extensive experience in the testing and development of most of the LNER express engines.

On his appointment, and new to the Railway, Bulleid immediately reviewed the steam locomotive stock and became aware of the shortcomings in the steaming of the Lord Nelson’s.  He ordered a redesign of the cylinders to enable an enlarging of the valve diameter, and had a multiple jet blast pipe installed.  These changes plus enlarged steam pipes made the steaming much better, and the Nelson’s became good reliable work horses for the rest of their days.

Bulleid then started to think about a really powerful locomotive that would, once and for all, sort out the Southern’s express engine problems.  He had seen the benefits of the large engine policy on the LNER but saw many express trains leaving the Southern’s termini still being double-headed, so he got a team together at Eastleigh and started working on designs for something really spectacular.

In 1938 Bulleid was authorised to prepare designs for twenty express passenger locomotives. The requirement was that the locomotive who be capable of hauling a 550-600 ton train at an average speed of 60 mph on the eastern Section and 70 mph on the Western Section.

His 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. Bullied had been closely involved with the project to design a P2 2-8-2 express locomotive whilst working for Gresley whilst at the London and North Eastern Railway.

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. 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. At one point Bullied was called to account by the Ministry of Labour who accused him of wasting valuable resources during the war by building streamlined express passenger locomotives. Bullied managed to convince the authorities that they were mixed traffic engines even though they were later classified as 8P by BR.

The first 4-6-2 pacific type locomotive to run on the Southern Railway was the Merchant Navy class, which was introduced under conditions of some secrecy during the Second World War in 1941. 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.

Bold, imposing and radical, the new Merchant Navy class brought Southern Railway locomotives into the modern age.  The air-smoothed casing – a new direction for Southern Railway motive power – tied in perfectly with the clean Art Deco styling of many Southern stations.

From a time when travelling by train was still the norm, the Southern gained much prestige with titled trains like the Atlantic Coast Express, promoting holiday journeys from London to the South-West’s sunny sandy beaches;  – and the locomotive hauling the train – possibly one of the 30 powerful Merchant Navy class locomotives.

The prototype was completed in February 1941, numbered 21C1 (21C1 – where 2 and 1 refer to the number of unpowered leading and trailing axles respectively, and C refers to the number of driving axles, in this case three. The remainder were numbered 21C2-21C19.), and named Channel Packet at a ceremony at Eastleigh works on 10 March 1941. It underwent extensive trials and minor modifications before joining Southern Railway stock 4 June 1941. A second prototype, 21C2 Union Castle was completed in June. Both prototypes were found to be seven tons over the specified weight, and, at the insistence of the Southern Railway Civil Engineer, production of the remainder was halted until steps were taken to remedy this. This was achieved by using thinner steel plates for the frame stretchers and covering the boiler cladding, and enlarging the existing lightening holes in the main frames. The remaining eight locomotives in the batch were delivered between September 1941 and July 1942.

A second batch of ten followed, beginning in December 1944 and culminating in June 1945. These were entirely constructed at Eastleigh and equipped with 5,100-imperial-gallon tenders. The Merchant Navy class spawned the design and construction of a lighter version of the same locomotive with consequently increased route availability – West Country and Battle of Britain class.

Just prior to the nationalisation of the railways in 1948, the Southern Railway placed an order for ten more Merchant Navy locomotives, with larger 6,000-imperial-gallon tenders. A shortage of materials meant that delivery was delayed until September 1948, and completed in 1949; the batch never carried Southern Railway numbers. Eastleigh was responsible for the assembly of the final batch, which were in the series 35021–35030. Construction was undertaken in-house by Eastleigh works, with the boilers and tenders constructed at Brighton, the frames at Ashford and the rest at Eastleigh. These were equipped with wedge-shaped cab fronts from the outset, and greater use of welding ensured lighter locomotives. The batch was also fitted with the TIA (Traitement Integral Armand) chemical feed-water equipment which precipitated scale-forming constituents in the hard-water of southern England into a non-adhesive mud that could be cleared from the locomotive using a manual blow-down valve. A delay in the construction of the new larger tenders for the new locomotives meant that some were fitted with the smaller tenders which were intended to be used for the West Country and Battle of Britain class locomotives being constructed at the same time.

Bullied fitted a modified type of Walschaert valve gear which was driven by a chain and was completely enclosed in an oil bath. A steam hydraulic reverser was fitted. The engine was fitted with BFB Boxpok cast steel wheels with holes and recesses on their discs (as also used on the Q1, Battle of Britain and West Country classes).

A modern, powerful boiler was fitted with welded steel firebox and two thermic syphons. The boiler pressure was originally 280psi but it was later reduced to 250psi. A multiple-jet blastpipe was fitted and an air-smoothed casing enclosed the boilers and cylinders.

In operation it was found that the corrosion of a water side of the inner firebox plates was more rapid than desirable and in 1947 a comprehensive and fully controlled water treatment was introduced. This was based on a French system which provides for water treatment in the tender which by adding compounds provides a sludge instead of scale and maintain in the water sufficient alkalinity to avoid ordinary corrosion.

All the engines carried the name of famous shipping lines, and they were known as the Merchant Navy class. Because of their air-smoothing casing they were irreverently known as Spam Cans.

The Merchant Navy locomotives were restricted in their route availability and the West Country and Battle of Britain classes were designed as a lighter version with wider route availability.

For its day the enclosed cab of the Merchant Navy was very comfortable, and well laid out for the driver and fireman. This included a steam operated fire-hole door, and turbine powered electric lighting for the headlamps, cabs, controls, and even under the casing; and the valve gear was encased in a sealed oil bath reducing the amount of oiling around that had to be done by the crew prior to a journey.  Though prone to slipping when starting, the powerful locomotives also gave a very smooth ride, and complementing the locomotives was new Bulleid designed passenger coaching stock.

The locomotives were introduced in matt finish Malachite green, with broad yellow lines, a matt black roof, and distinctive name and number plates made from brass castings with a red painted background.  Two variations of experimental blue were also tried, but Wartime black livery did this class no favours, giving them a very slug like appearance.

As the class appeared during the War, there were no heavily laden Continental Boat Trains from Dover and Folkestone, for which they had been designed. They were however used on express trains on the South Western Main Line to Southampton, and Exeter. In August 1945 a series of test runs were made between London Victoria and Dover and from October the class were used on the resumed Continental expresses. The prestigious Bournemouth Belle Pullman train was reinstated in October 1946 and entrusted to the class for the next two decades. However, their heavy axle loading and length meant that they were banned from many areas of the Southern Railway, and later, the British Railways Southern Region network.

As mentioned, the main production batch of Southern-built locomotives differed from the two prototypes, Channel Packet and Union Castle. The steam-operated firehole door treadle was removed, and a new type of boiler cladding was utilised in response to the worsening supply situation during the Second World War. Modification was also made to the air-smoothed casing surrounding the smokebox after reports were made of drifting smoke obscuring the locomotive crew’s vision ahead. Initially, the only form of smoke deflection was a narrow slot in front of the chimney, intended to enable air to lift the smoke when the locomotive was travelling. This proved inadequate because of the relatively soft exhaust blast that came from the multiple-jet blastpipe, which failed to be caught by the air flow. After several trials, the air flow was increased by extending the casing roof over the front of the smokebox to form a cowling whilst side smoke deflector plates were also incorporated into the front of the air-smoothed casing. The latter added to the poor visibility from the footplate and the expedients combined never fully solved the smoke drift problem.

During the brief time they operated under the Southern Railway, further modifications were applied to the class, such as the reduction in boiler pressure to 250 psi and the redesign of the footplate spectacle plates. These are the small windows on the front face of the cab, which were redesigned to a wedge-shaped profile, a feature to be seen on all Bulleid-designed locomotives post-nationalisation. They had been introduced in Britain in 1934 with the Gresley designed Cock o’ the North. Originally, the spectacle plates of the Bulleid pacifics were at the conventional right-angle to the direction of the locomotive, and offered limited vision ahead along the air-smoothed casing. The Southern-built batches also had variations in the material used for the air-smoothed casing with a change from sheet steel to an asbestos compound, forced upon the manufacturer by wartime expediency. This resulted in several class members having a horizontal strengthening rib running down the length of the casing. The final Southern Railway-initiated experiment involved equipping 21C5 Canadian Pacific with a Berkeley mechanical stoker imported from Canada. Little improvement in performance was seen when trialled under British Railways auspices in 1948 and the locomotive was re-converted to hand-firing.

As mentioned, the British Railways batch had detail differences to previous versions. The most significant modification was the reduction of weight using lighter materials unavailable during wartime. From 1952 the air-smoothed casing ahead of the cylinders was removed to ease maintenance and lubrication. This coincided with the removal of the tender raves on all locomotives, as they obstructed the packing of coal into the bunker and restricted the driver’s view when reversing the locomotive. The resultant cut-down tender included new, enclosed storage for fire-irons, revised step ladders and glass spectacle plates to protect the crew from flying coal dust when running tender-first.

The new locomotives demonstrated that they could generate enormous power using mediocre quality fuel, due largely to Bulleid’s excellent boiler. They also ran very smoothly at high speed. Partly as a result of having so many novel features, the first few years of service by the Merchant Navy class were beset by a variety of technical problems. Some of these were merely teething troubles, but others remained with the class throughout their working lives. At their best the Merchant Navy class engines were as strong and fast as any engines in the country, at their worst they were a nightmare. These may be summarised as follows:

  • Adhesion problems. The locomotives were often prone to wheelslip, and required very careful driving when starting a heavy train from rest, but once into their stride they were noted for their free running, excellent steam production and being remarkably stable when hauling heavy expresses.
  • Maintenance problems. The chain driven valve gear proved to be expensive to maintain and subject to rapid wear. Leaks from the oil bath onto the wheels caused oil to splash onto the boiler lagging in service. Once saturated with oil, the lagging attracted coal dust and ash which provided a combustible material, and as a result of the heavy braking of the locomotives, sparks would set the lagging on fire underneath the air-smoothed casing. The fires were also attributed to oil overflowing from axlebox lubricators onto the wheels when stationary to be flung upwards into the boiler lagging in service. In either case, the local fire brigade would invariably be called to put the fire out, with cold water coming into contact with the hot boiler, causing stress to the casing.
  • High fuel consumption. This became very apparent in the 1948 Locomotive Exchange Trials and at trials at the Rugby locomotive testing plant in 1952.
  • Restricted driver visibility due to the air-smoothed casing. The exhaust problem was never adequately resolved, and continued to beat down onto the air-smoothed casing when the engine was on the move, obscuring the driver’s vision from the cab.
  • As a result of these problems serious consideration was given to scrapping the class in 1954, and replacing them with Britannia class locomotives. However, the locomotives had excellent boilers and several other good features and so the decision was taken to rebuild them removing several of Bulleid’s less successful ideas.

On 24 April 1953 the crank axle on the central driving wheel of 35020 Bibby Line fractured whilst approaching Crewkerne station. 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 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.

The incident resulted in the withdrawal of all Merchant Navy class locomotives from service whilst the cause was ascertained. An examination of other class members showed that the fracture, caused by metal fatigue, was a common fault. To cover the motive power shortage caused by the mass withdrawal of thirty locomotives, classes from other British Railways regions were drafted in to deputise (Britannias, ex-LMS Class Fives, ex-LNER V2s and B1s, were despatched to both South Western and South Eastern Divisions of the Southern Region).

Partially because of the Crewkerne incident, and due to the incessant modification of Bulleid’s original design, British Railways took the decision to rebuild the entire class to a more conventional design by Jarvis, adopting many features from the BR Standard locomotive classes that had been introduced since 1950. The air-smoothed casing was removed and replaced with conventional boiler cladding, and the chain-driven valve gear was replaced with three separate sets of Walschaerts valve gear. The rebuilds were provided with a completely revised cylindrical smokebox, a new Lord Nelson-type chimney and LMS style smoke deflectors. Together with the lack of air-smoothed casing, these helped reduce the problem of smoke and steam obscuring the driver’s vision of the line.

The fast-moving and unpredictable Bulleid steam reverser was replaced with a screw-link version, whilst the mechanical lubricators were moved to the footplates along the boiler sides. Sanding was also added to the leading driving axle, whilst rearward application was incorporated to the middle driving axle. The first rebuilt member of the class to be released from Eastleigh was 35018 British India Line in 1956. The final example, 35028 Clan Line, was completed in 1960. The success of the modification programme for the Merchant Navy class was also to influence the design of the future modification of 60 West Country and Battle of Britain class.

The rebuilding of the class solved most of the maintenance problems whilst retaining the good features, thereby creating excellent locomotives. One minor drawback was that the rebuilt locomotives put greater loads on the track as a result of hammerblow, caused by the balance weights for the outside Walschaerts valve gear, whereas the original valve gear design was largely self-balanced.

On 26 June 1967, 35003 Royal Mail recorded the highest speed ever for the class. Hauling a train comprising three carriages and two parcels vans (164 tons tare, 180 tons gross) between Weymouth and Waterloo, the mile between milepost 38 and milepost 37 (located between Winchfield and Fleet) was covered in 34 seconds, a speed of 105.88 mph. This was also the last authenticated speed in excess of 100 mph achieved by a steam locomotive in the United Kingdom.

As of 1959, three MN class engines were allocated to the South Eastern Division, all based at Stewarts Lane. In addition, ten were based at Nine Elms, seven at Bournemouth, seven at Exmouth Junction, and finally, three at Salisbury. The start of full-accelerated electric timetables on Kent Coast Lines (first the Chatham main line to Dover in 1959, followed by the ex-SER trunk route via Tonbridge and Ashford in 1962), meant that steam became virtually extinct on the South Eastern Division. The remaining Bulleid pacifics were transferred to the South Western Division, where steam traction had yet to be fully ousted. A large blow to the SR Pacific fleet came on 15th September 1962, when all Southern Region lines west of Salisbury were brought under the control of Paddington and the Western Region introduced the Warship class diesel-Hydraulic. Thus, all those engines based at Exmouth Junction, including the seven MNs, were absorbed into the Western Region fleet. Of those MN locomotives, just one, 35009 Shaw Savill, was withdrawn by the WR during the elimination of steam traction in the Exeter area, in September 1964. The other six members made their way back to the Southern Region, all but one (35011 General Steam Navigation) remaining in service until summer 1967.

In September 1964, the Minister of Transport authorised the electrification of the South Western Division main line from Brookwood to Branksome, Dorset (just west of Bournemouth), on the familiar third rail system. This completely eliminate steam from the SR; beyond Bournemouth, diesel-electric traction was used.

Full electric working to Bournemouth was planned to commence on 10th June 1967, but was put back by exactly a month following delays in the delivery of electric rolling stock. 9th July 1967 was the final day of steam working from Waterloo, by which time seven MN engines were still in service: 35003, 35007, 35008, 35013, 35023, 35028, and 35030 but only one of these (35028 Clan Line which was the last to be rebuilt) was subsequently preserved.

The rebuilt locomotives were therefore withdrawn relatively soon after their rebuilding, whilst still in excellent condition. When they were rebuilt it was anticipated that steam would remain on BR until 1990 when it would be replaced by electric traction.

The first two to be withdrawn were the second prototype 35002 Union Castle and 35015 Rotterdam Lloyd in February 1964. Nearly half of the class had been withdrawn by the end of 1965, but seven survived until the end of steam on the Southern Region in the summer of 1967.

Number in Service.

Built Rebuilt Withdrawals No. in Service
BR Numbers Quantity As Built


1941 35001-6



1942 35007-10



1944 35011-12



1945 35013-20



1948 35021-28



1949 35029-30


































Allocation of locomotives in service as at 1st of January.


1948 1955 1960 1965




  2   8


Dover Marine


Exmouth Junction


  8   7


Nine Elms


12 12




  3   3


Stewarts Lane






30 30 23


The locomotives allocated to work on the Eastern Section were transferred to the Western Section following the electrification of the Kent coast line in 1961.

Accidents and Incidents

On 17th December 1942 21C6 Peninsular & Orient Oriental S. N. Co. was hauling an Exeter to Salisbury goods train near Honiton when one of its valve gear chains broke and thrashed around in the oil bath, setting fire to the boiler lagging and lineside vegetation.


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