SR Merchant Navy class

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SR Un-rebuilt Merchant Navy Class[1]
Official Southern Railway photograph of 21C1 Channel Packet as built, 1941.
Type and origin
Power typeSteam
DesignerOliver Bulleid
BuilderSR Eastleigh Works
Build date1941–1949
Total produced30
Specifications
Configuration:
​
 • Whyte4-6-2 (Pacific)
GaugeTemplate:4ft8.5in
Length69 ft 8 in (21.85 m)
Fuel typecoal
Fuel capacity5 tons (5.1 tonnes)
Water cap.5000 imp. gal (22700 litres)
Boiler pressure280 lbf/in² (1,930 kPa)
Cylinders3
Cylinder size18 in × 24 in (41.6 cm × 61 cm)
Performance figures
Tractive effort37,513 lbf (166.86 kN)
Career
LocaleGreat Britain

The SR Merchant Navy Class, also known as Bulleid Pacifics, Spam Cans or Packets, was a class of air-smoothed 4-6-2 Pacific steam locomotive 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 Packets were amongst the first British designs to utilise welding in the construction process, and to use steel fireboxes with thermic syphons, which allowed for efficient steam production and meant that components could be more easily constructed during the wartime austerity and post-war economy.[2] The class members were named after Merchant Navy shipping lines involved in the Battle of the Atlantic, and latterly those which used Southampton Docks. This was an astute publicity masterstroke for the Southern Railway.

Due to problems with some of the more novel features of Bulleid's design, all members of the class were subsequently rebuilt by British Railways during the late 1950s, losing their air-smoothed casings in the process. The Packets operated until the end of Southern steam in July 1967. One third of the class avoided being scrapped, and they can be seen on heritage railways throughout Great Britain.

Background

The gestation of the Merchant Navy Class Pacifics began in 1938, when Sir Eustace Missenden, the Director of the Southern Railway, realised that the company lagged behind in terms of pioneering locomotive design.[3] Bulleid, who had been brought in from the LNER to replace Richard Maunsell as Chief Mechanical Engineer (CME) believed that it was time for the Southern to lead the field with the construction of an eight-coupled machine (an engine with four driven axles). This was due to the fact that the newest locomotive class on the railway was an 0-6-0 Q Class that was built to Victorian design principles.[4] The first suggestion was for an eight-coupled locomotive of the 4-8-2 wheel arrangement, although this was quickly modified to a 2-8-2, equipped with a Helmholz "Bissel-Bogie"[3], a system already applied with some success on the continent, where a leading pair of carrying wheels shared a frame pivoted frame similar to that of a bogie; in a curve this compensated the radial movement of the carrying wheel by sliding the leading coupled wheel laterally over to the opposite side [5]. However, both of these proposals were resisted by the Southern Railway's Chief Civil Engineer, so a new 4-6-2 Pacific design was settled upon instead.[6] Intended primarily for express passenger and semi-fast work in Southern England, the new class was also designed to be equally adept at freight workings due to the nominal mixed traffic classification Bulleid applied to the class for them to be built in wartime. This was because administrative measures had put in place by the wartime government, preventing the construction of express passenger locomotives due to the lack of materials and a need for more locomotives with freight-hauling capabilities.[7]

Design features

The distinctive Bulleid-Firth-Brown wheels, seen here on 35010 Blue Star. Note the balance weight on the lower right, a feature not present on the MNs as-built.

The Merchant Navy Class design was originally intended to used gear-driven valve gear, though space restrictions for the inside motion and wartime material shortages led Bulleid to designed his novel chain-driven valve gear.[8] This component was unique amongst British locomotive design practices.[9] It gained a bad reputation because it could cause highly irregular valve movements, a problem compounded by the fast-moving Bulleid steam reverser. The entire system was located in a sealed oil bath, another unique design, that provided constant lubrication to the moving parts;[10] however it was difficult to access when things went wrong.[8] A number of other features were unusual when compared to other contemporary designs. The inner firebox was constructed with Bulleid's revolutionary use of welding, as opposed to the rivetting that was more common practice. This made for cheaper construction and easier maintenance, whilst thermic syphons were implemented to improve the efficiency of water flow in the boiler.[8] Maximum boiler pressure was higher than any other regular service locomotive, at 280psi.

The boiler was enveloped by Bulleid's air-smoothed sheet steel casing, whilst the locomotive sat on the unusual Bulleid-Firth-Brown wheels, which were lighter, yet stronger than the spoked equivalent. The air-smoothed casing was not regarded as streamlining, a fact demonstrated by the extremely flat front end, but as an aid to cleaning the locomotive via the use of a carriage washer, representing another attempt to reduce labour during the post-war period.[11] Electric lighting was also provided, powered by a steam generator below the footplate, as well as a steam-operated treadle that used steam pressure to open the firehole doors as an aid to the fireman.[8] The tender could carry 4,500 gallons of water and featured streamlining panels, or "raves", that gave the top of the tender a similar cross-sectional outline to the carriages hauled by the locomotive.[10]

The footplate was frequently regarded by crewmen as ergonomically superior to other express passenger locomotives of the period, as the controls required for operation were grouped according to the needs of both fireman and driver.[8] Other innovations provided on the footplate included electric lighting and gauges lit by ultra-violet light, which enabled clearer night-time vision of the boiler steam pressure gauge and the brake pipe vacuum pressure gauge whilst eliminating dazzle, thus making it easier to spot signals.[8] The footplate was also entirely enclosed, improving crew working conditions in winter, and the supporting trailing wheels gave the smoothest of rides; their design was utilised in the future BR Standard Class 7.

Exhaust problems and early modifications

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.[12] 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 deflection was a narrow slot in front of the chimney, which enabled air flow to lift the smoke when the locomotive was traveling. This proved inadequate because of the relatively soft exhaust blast that came from the multiple-jet blastpipe, which failed to be adequately caught by the air flow.[13] After several trials, the best solution was to extend the casing roof over the front of the smokebox to form a cowling, which caught the rush of air, directing it up towards the chimney, lifting the exhaust clear. Smoke deflectors were also incorporated into the front of the air-smoothed casing, though these added to the problem of the lack of visibility from the footplate.[14]

Further modifications were applied to the class during the brief time they operated under the Southern Railway, such as the redesign of the footplate spectacle plates. These are the small windows in the front face of the cab, which were redesigned to the angled profile that all Bulleid-designed locomotives depict post-Nationalisation. Originally, the spectacle plates were at right-angles to the air-smoothed casing, offering limited vision ahead for the driver.[15] 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.

Construction history

The Southern Railway initially constructed ten Packets at Eastleigh Works: the first to be completed in March 1941 was number 21C1 Channel Packet. A second batch followed, beginning in 1944 with 21C11 General Steam Navigation, and culminating with 21C19 French Line C.G.T. in September 1945, and were equipped with 5,100 gallon tenders.[16] The final ten engines in the class were constructed after the nationalisation of the railways in 1948.[10] This meant that they never carried Southern Railway numbers. The British Railways batch had detail differences to previous versions, the most significant being the tender, which had an increased water capacity of 6,000 gallons.[17] The Merchant Navy Class spawned the design and construction of the West Country and Battle of Britain Classes, from 1945, constituting a lighter version of the same locomotive, which helped increase the route availability. They were required for use on the Southern's "Withered Arm" west of Exeter, as the heavier Merchant Navy Class locomotives were banned from this section due to weight restrictions.[8]

Naming the locomotives

The Southern Railway considered naming the locomotives after victories of the Second World War, to the extent that a mocked-up nameplate River Plate was produced.[18] In the event, the chairman of the Union Castle Line suggested naming them after shipping companies which had called at Southampton Docks in peacetime.[19] This idea had more suitability in 1941 due to the fact that the shipping lines were heavily involved in the Atlantic convoys to and from Britain during the Second World War.[18] A new design of nameplate was created, featuring a circular plate with a smaller circle in the centre, which carried the colours of the shiiping company on a stylised flag on an airforce blue backgroung. Arount the centre circle was the name of the locomotive, picked out in gilt lettering. Two horizontal rectangles were attached to the edge of the neamplate, with "Merchant Navy Class" in gilt lettering. This acted as a class plate. During their operational career, the Packets gained several nicknames; the most obvious, Bulleid Pacific, simply denoted the designer and wheel arrangement. The colloquial name Spam Can arose from their utilitarian appearance, enhanced by the flat, boxy air-smoothed casing, and the resemblance of this to the distinctive tin cans that SPAM was sold in. The nickname Packets was also adopted by locomotive drivers, as the first member of the class was named Channel Packet.

The British Railways engines

The final batch of ten locomotives constructed after the nationalisation of Britain's railways never carried a Southern Railway number.[10] The British Railways standard numbering system placed this batch in the series 35021–35030, with all locomotives completed at Eastleigh between 1948–1949.

BR Rebuilt Merchant Navy Class[1]
Rebuilt 35024 East Asiatic Company at Exeter St Davids, 1962 with Atlantic Coast Express headboard.
Type and origin
Power typeSteam
DesignerR. G. Jarvis after Oliver Bulleid
BuilderSR Eastleigh Works
Build date1956–1960
Total produced30
Specifications
Configuration:
​
 • Whyte4-6-2 (Pacific)
GaugeTemplate:4ft8.5in
Length71 ft 7 in (21.85 m)
Fuel typecoal
Fuel capacity5 tons (5.1 tonnes)
Water cap.6000 imp. gal (27240 litres)
Boiler pressure250 lbf/in² (1,723 kPa)
Cylinders3
Cylinder size18 in × 24 in (41.6 cm × 61 cm)
Performance figures
Tractive effort33,495 lbf (148.99 kN)
Career
LocaleGreat Britain

Rebuilding

Between 1956 and 1960, British Railways rebuilt the entire class to a more conventional design by R. G. Jarvis, adopting many features from the BR 'Standard' locomotive classes that had been introduced.[20] The air-smoothed casing was removed and replaced with conventional boiler cladding, and the chain-driven valve gear was replaced with modified Walschaerts valve gear, whilst the boiler pressure was reduced from 280 to 250psi. The first to be released from Eastleigh was 35018 British India Line in 1956. The final example, 35028 Clan Line, was completed in 1960. The rebuilt Merchant Navy Class was also to influence the design of the future rebuilding of 60 Light Pacifics.

As a result of the rebuilding and the implementation of Walschaerts valve gear, the rebuilts were prone to hammerblow on the track due to the balancing required to operate the valve gear.[10], a complaint that was not evident with as-built locomotives. The rebuilt locomotives were scrapped relatively soon after their rebuilding, an indication of the waste in resources made by British Railways, as some engines such as 35014 Rotterdam Lloyd were withdrawn as early as 1964.[8] The last few engines in traffic survived until the end of steam on the Southern Region in the summer of 1967.

Operational details

The utilisation of welded steel construction and several innovations that had not previously been seen in British locomotive design meant that the class earned Bulleid the title 'Last Giant of Steam'.[21] The constant concern for ease of maintenance and utility had not previously been seen on locomotives of older design, whilst their highly efficient boilers represented the ultimate in British steam technology, the hallmark of a successful locomotive design.[22] The locomotives were largely successful, though their heavier axle loading meant that they were banned from certain areas of the Southern Railway, and later, the British Railways Southern Region network. 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.[8]

A perennial problem with the un-rebuilt Merchant Navy Class locomotives lay with the leaks from the oil bath onto the wheels that in turn splashed oil 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.[23] 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 casings. Many photographs show an un-rebuilt with "cockled" (warped) casings, a result of a lagging fire.[10]

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.[24] The rebuilts were provided with LMS-style smoke deflectors and the lack of air-smoothed casing also helped reduce the problem.[25]

Livery and numbering

Southern Railway

Livery was Southern Railway Malachite green with Sunshine Yellow horizontal lining and lettering. All class members that operated during the Second World War were eventually repainted in Southern Railway Wartime Black livery, with green shaded 'Sunshine' lettering. However, this was reverted back to Malachite Green upon the ending of hostilities.

21C1 Channel Packet originally had an inverted horseshoe on the smokebox door, indicating its Southern origin, however, locomotive crews believed this to be unlucky. A resultant re-design meant that this became a roundel, the gap being filled by the date and place of construction, therefore acting as a builder's plate. The background was painted red. Early members of the class had cast iron numberplates and gilt 'Southern' plates on the tender, however these were subsequently replaced by transfers.

Bulleid advocated a continental style of locomotive numbering, based upon his experiences at the French branch of Westinghouse Electric before the First World War, and those of his tenure in the rail operating department during that conflict. The Southern Railway numbers followed an adaptation of the UIC classification system 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. All the locomotives of Pacific wheel arrangement therefore carried the prefix 21C, followed by the number in the group.[26]

Post-1948 (nationalisation)

Initial livery after nationalisation in 1948 was modified Southern malachite green and sunshine yellow with British Railways on the tender, and the Bulleid numbering system was temporarily retained with an "S" prefix such as S21C1. The second livery carried was the British Railways Experimental Express Passenger Blue with red or white lining, and was carried until 1952. From then on, the locomotives carried British Railways Brunswick Green livery with orange and black lining, and this livery was perpetuated after rebuilding. The locomotives were renumbered under the British Railways standard system in the series 35001–35030 from 1949.[27] Rebuilt locomotives were also outshopped in BR Brunswick Green, with the BR crest on the tender sides.

Preservation

Many of the class have survived into preservation thanks to the famous Barry Scrapyard in South Wales, where steam engines bought from British Railways for scrapping were stored, rather than immediately cut up. One engine, 35028 Clan Line, was bought by the Merchant Navy Locomotive Preservation Society direct from British Railways in 1967, and has since been regarded as the 'flagship' of the class.[10] A third of the Packets have survived into the preservation era, although it is very likely that many will never steam again, with only three having been restored to working order thus far. This is due to the fact that the class is too large and heavy for use on most of today's heritage railways. As the entire class was rebuilt from 1956 onwards, no Merchant Navy Class locomotives exist in as-built condition.

Preserved Merchant Navy Class locomotives

Number 35010 Blue Star on Static display awaiting restoration at the Colne Valley Railway
For location details of the preserved locomotives, see: List of SR Merchant Navy Class locomotives

Footnotes

  1. ^ a b Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class Cite error: The named reference "Harvey" was defined multiple times with different content (see the help page).
  2. ^ Arlett, Mike: "The Train Now Departing", p. 29–30
  3. ^ a b Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, p. 9 Cite error: The named reference "Harvey1" was defined multiple times with different content (see the help page).
  4. ^ Morgan, John Scott: The Story of the Q1s, p. 9
  5. ^ Chapelon A : “La Locomotive à Vapeur” (English ed., transl. Carpenter George W.); Camden Miniature Steam Services, Somerset U.K. (2000) ISBN 0 9536523 0 0, pp. 110-111
  6. ^ Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, pp. 6–9
  7. ^ Creer,S & Morrison,B: The Power of the Bulleid Pacifics, p. 7
  8. ^ a b c d e f g h i Bulleids in Retrospect, Transport Video Publishing, Wheathampstead, Hertfordshire.
  9. ^ Chain-driven valve gear diagram retrieved April 13, 2007
  10. ^ a b c d e f g Herring, Peter: Classic British Steam Locomotives, pp. 156–157
  11. ^ Creer,S & Morrison,B: The Power of the Bulleid Pacifics, p. 21
  12. ^ Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, 21
  13. ^ Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, 25
  14. ^ Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, 40
  15. ^ Creer,S & Morrison,B: The Power of the Bulleid Pacifics pp. 40-41
  16. ^ Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, 33
  17. ^ Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class, 37
  18. ^ a b Burridge, Frank: Nameplates of the Big Four, p. 61
  19. ^ Southern E-Group (2004) Bulleid MN "Merchant Navy" Class 4-6-2, Retrieved April. 16, 2007. For details of the naming process.
  20. ^ Southern E-Group (2004) Rebuilt Bulleid MN "Merchant Navy" Class 4-6-2, Retrieved April 16, 2007. For more pictures of the rebuilt locomotives.
  21. ^ Day-Lewis, S.: Bulleid, Last Giant of Steam (1964), p. 7
  22. ^ Whitehouse, Patrick & Thomas, David St.John: SR 150: A Century and a Half of the Southern Railway p. 47
  23. ^ Southern E-Group (2004) Bulleid MN "Merchant Navy" Class 4-6-2: Notes from a Bulleid Fundamentalist, Retrieved April 16, 2007. For details on the lagging fires, they were common to both Merchant Navys and 'Light Pacifics'.
  24. ^ Creer,S & Morrison,B: The Power of the Bulleid Pacifics, p. 13
  25. ^ Creer,S & Morrison,B: The Power of the Bulleid Pacifics, pp. 74-75
  26. ^ Burridge, Frank: Nameplates of the Big Four, p. 60
  27. ^ Ian Allan ABC of British Railways Locomotives, winter 1958–59 edition

References

  • Bulleid, H. A. V.: Bulleid of the Southern (Hinckley: Ian Allan Publishing, 1977) ISBN 071100689X
  • Burridge, Frank: Nameplates of the Big Four (Oxford Publishing Company: Oxford, 1975) ISBN 0902888439
  • Creer,S & Morrison,B: The Power of the Bulleid Pacifics (Oxford Publishing Company: Oxford, 2001) ISBN 0860930823
  • Chapelon A : “La Locomotive à Vapeur” (English ed., transl. Carpenter George W.); Camden Miniature Steam Services, Somerset U.K. (2000) ISBN 0953652300
  • Day-Lewis, S: Bulleid, Last Giant of Steam (London: George Allen & Unwin, 1964) P. 186
  • Harvey, R. J.: Bulleid 4-6-2 Merchant Navy Class (Locomotives in Detail series volume 1) (Hinckley: Ian Allan Publishing, 2004), ISBN 0711030138
  • Herring, Peter: Classic British Steam Locomotives (Abbeydale Press: London, 2000) Section "Merchant Navy Class" ISBN 1861470576
  • Ian Allan ABC of British Railways Locomotives, winter 1958–59 edition
  • Morgan, John Scott: The Story of the Q1s (KRB Publications: Bishop's Waltham, 2003) ISBN 0954485912

Further reading

  • Ian Allan ABC of British Railways Locomotives, winter 1962–63 edition
  • Morrison, B: The Power of the Merchant Navies (Oxford Publishing Company: Oxford, 2007) ISBN 0860936074
  • Reed, B: “Merchant Navy Pacifics” Loco Profile series 22, page 231 (Profile publications, Berkshire, England, 1972)

See also

External links

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