LN 4-6-0 SR Maunsell Lord Nelson 30850 – 30865

LN

Power Classification 6P reclassified 7P in 1951
Introduced 1926 – 1929
Designer Maunsell
Company SR
Weight – Loco 83t 10cwt
               Tender 57t 19cwt
Driving Wheels 6ft 7ins
Boiler Pressure 220psi superheated
Cylinders Four – 21.5in x 26in
Tractive Effort 33,510lbf
Valve Gear Walschaert (piston valve)

In 1923 upon becoming the Chief Mechanical Engineer of the newly formed Southern Railway Richard Maunsell assessed the locomotive stock inherited from the pre-grouping companies. He found there was 2,285 locomotives spread across 125 different classes and with an average age of 28 years.

As was becoming common at the time he proposed a range of nine standard locomotives to meet the future needs of the railway with a large degree of commonality of engineering design and parts. His top express passenger locomotive for the range was planned to be a 4-cylinder 4-6-0 locomotive. This 4-6-0 was eventually to be called the Lord Nelson class and all were named after famous British Admirals.

Short term requirements dictated that Maunsell first of all had to produce an improved version on the N15 design introduced by Urie in 1918. This he did with his developments introduced in 1925.

He was set a tough challenge for this specification of an express passenger locomotive by the Chief Operating Manager because the future standard for main line express trains was to haul a load of 500 tons tare at a start-to-stop average speed of 55 mph, so as not to impede the congested electrified lines around London. This was not only the South West section but also over the demanding to operate Eastern section. This was because although the improved King Arthur class 4-6-0 locomotives were capable of the heaviest express passenger work between London and South-West England, there was a growth in demand for Continental traffic travelling via Dover and Folkestone. However, any enlargement of the existing 2-cylinder design was not possible due to weight restrictions imposed by the railway’s Civil Engineer.

In 1923 the best time the average speeds being achieved were-

  • London – Salisbury – 54mph
  • London – Southampton – 51mph
  • London – Folkstone – 53mph
  • London – Margate – 48mph

It needs to be remembered that the loads behind the locomotive when these speeds were achieved was less than the 500 tons for which the 55mph target was to apply as loads of 500tons was rare anywhere on the railways of Britain.

Maunsell set about this in a systematic fashion with development work and trials using modified locomotives, and evaluating and comparing the designs of other companies with the aim of producing what would be called today a “state of the art” locomotive. However, first there was a pressing need for more express passenger locomotives for the expanded summer timetable of 1925 and this was met by construction of additional class N15 engines with an improved front end.

 N15 N15 as developed by Maunsell and introduced in 1925.

Two questions figured large in the thinking of those involved with designing the new engines to meet the challenge set. These were should the locomotives be based 4-6-0 or 4-6-2 wheel arrangements and should it have three or four cylinders. On the former the thought was that a 4-6-0 with a narrower firebox than the GWR Castle class would be cheaper. The narrower firebox being considered possible because the Southern Railway locomotives were not required to undertake as long a journey as the Castles on the GWR. Clayton, who was heavily involved in the design of the locomotive, favoured using four cylinders as employed by Churchward on the GWR.

Holcroft, who was Clayton’s junior partner, put a paper to the Institute of Locomotive Engineers in 1920 entitled “Four-Cylinder Locomotives” in which he put forward a proposal that the crank shaft could be set at 135 degrees which would give eight exhaust per revolution of the driving wheels. This was then tested on a Drummond 6ft 4-6-0 locomotive and the performance using the Holcroft proposal was found to make a significant improvement to the performance of the engine.

Work began in earnest in designing the locomotive in the autumn of 1924. In October of that year Clayton rode on the footplate of Castle class 4076 Carmarthen Castle from Paddington to Plymouth at the head of the Cornish Riviera Express. Ten days later he was on the footplate of the Flying Scotsman between Kings Cross and Grantham. These confirmed the view that Clayton had that the new Southern Railway locomotive should be of a 4-6-0 design.

So after the considerations of various options the eventual specification called for a four cylinder 4-6-0 locomotive with cranks set at 135 degrees, the drive divided between the first two coupled axles, 6 ft 7 in diameter driving wheels, a boiler pressure of 220 lb psi and a tractive effort of 33,500 lb – the highest of any British express passenger locomotive of the time. One original feature was the settings of the cranks led to eight power impulses per revolution in place of the normal four, leading to eight exhausts for every revolution of the driving wheels. This applied to all except the last of the class, 30865, which has the more normal four exhaust per revolution. A Belpaire firebox was employed and although a longer boiler had been considered earlier a boiler with tubes the same length as those employed on the N15 class was used. The fire grate was to be unique to the Southern (but not to the GWR) with the rear portion being horizontal and the front steeply inclined providing an area of 33 sq ft, the largest of any British locomotive of the time (although later exceeded by the GWR King class). Because the four-cylinder design threatened to result in a locomotive heavier than the Civil Engineer’s axle loading limit special care was taken in design and construction to keep the locomotive’s weight to a minimum. The drive was divided between the front coupled axle for the inside cylinders and the middle coupled axle for the outside cylinders giving better weight distribution and reduced hammer blow. High tensile steel was employed for the motion. Parts which would normally have been left as cast or forged were machined to remove excess metal and the frames were made as thin as practical with additional lightening holes. When constructed the prototype locomotive came out only 1 ton 1 cwt heavier than the N15 class so production models did not employ the latter two weight reducing factors. An increase of almost 33 percent tractive effort for only just over a 1 ton weight gain between the two classes is a tribute to the skilful design. The LMS 4-6-0 Royal Scot class introduced in the 1930s was loosely based on this design.

LN

Lord Nelson class
 RS as introduced Royal Scot class as originally introduced in 1927.

The pressing needs of the Traffic Department for the 1925 summer service made it necessary to but the project for a new locomotive to one side as the only way to meet the needs of the peak traffic in 1925 would be to build more engines of an existing design. As a result a further batch of N15 (King Arthur) class 4-6-0 engines were order to be built by the North British Locomotive Company.

The prototype was built at Eastleigh in 1926, numbered E850 and was named very popularly after Lord Nelson – which was eventually to become the designation of the whole class. Maunsell then trialed the prototype in service for two years and only minor modifications to the front end were required for the production run. The trials indicated that the design was capable under ideal operating conditions of meeting the 500 ton/55 mph specification but in reality it was never required since the deteriorating economic conditions in the country resulted in the loading of services never reaching this limit. In fact the heaviest and fastest services of the day remained within the capabilities of the King Arthur (N15) class.

An initial order for ten more locomotives for delivery between May 1928 and April 1929 was placed following the trials. These were originally scheduled to be allocated to Battersea depot and fitted with 4,000 gallon 6-wheeled tenders suitable for the Continental ports. However, during construction, it was decided to equip half of the class with 5,000 gallon 8-wheeled tenders necessary for the longer West of England routes and to allocate them to Nine Elms depot. A further batch of ten locomotives was ordered in 1928, before the previous batch had been delivered, but when it became apparent that the Stock Market Crash of 1929 would be likely to reduce the demand for Continental travel, this second order was reduced to five.

In service the Lord Nelsons were found to be not as free steaming as the King Arthur class which remained the majority of footplate crews’ favourite. Performance of the class could be erratic and this was attributed to unfamiliarity with its firing needs. In the hands of an experienced LN crew exceptional performances could be obtained (though on the SW main line it was noted the class always performed far better east of Salisbury than on the demanding section to the west). That there were only ever sixteen engines of the class contributed to the unfamiliarity with the locomotives by the majority of crews. Despite this the Lord Nelson class was always highly regarded and the contribution to advances in British locomotive design by Richard Maunsell with this class should never be underestimated. The class proved to be very reliable in service and as such it was popular with shed staff.

Once in service five engines were modified in different ways to trial further improvements. This included fitting 30859 with smaller driving wheels, fitting 30860 with a longer boiler whilst 30865 had its crank adjusted to give the more normal four exhausts per revolution of the driving wheels.  None of these provided any significant change in performance and whilst the modifications were not extended to any other members of the class they were never removed from their trial locomotives. In 1931 authority was given for a sixth trial to modify a Lord Nelson class locomotive to a four-cylinder compound with a 250 lb pressure boiler and poppet valves but this was not pursued. As with the N15 and S15 classes various type tenders were exchanged and six wheeled tenders were used on the Eastern section.

In the late 1920s the entire class were fitted with smoke deflectors.

Maunsell was aware of the reputation for poor steaming enjoyed by the class and attempted to address it by the fitting of twin Kylchap blastpipes to No. 860 in 1934. Upon succeeding Maunsell in 1937,  Bulleid improved the class by fitting Lemaître multiple jet blastpipes and larger diameter piston valves. He also introduced the final design of tender, still with 5,000 gallons capacity but with a sharper slope to the bunker floor which helped make the coal tumble forwards more easily. The sides were raised which increased the depth of the bunker. The class was due to be relegated by the arrival of Bulleid’s own pacifics but when his new locomotives had problems the Lord Nelsons deputised, on routes they were allowed to work, and proved their continuing worth.

The Lord Nelsons were notoriously difficult for inexperienced crews to fire properly, due to their long firebox, and specific crews who had proven experience in firing the locomotives were therefore allocated to them. This was due to the relatively few locomotives in the class for crews to train on.

From 1959 onwards the entire class was based at Eastleigh where they finished their days working the Waterloo-Southampton boat trains and the Waterloo-Bournemouth services.

Once BR had rebuilt the Bullied Pacifics the Lord Nelson class finally became relegated from top link duties and withdrawals began in 1961 with the whole class being withdrawn by the end of 1962.

Only the prototype 30850 (850) has been preserved and is under the care of the Eastleigh Railway Preservation Society.

Number in Service.

Built

Withdrawals No. in Service
BR Numbers Quantity
1926 30850

 1

  1

1928 30851-57

 7

  8

1929 30858-65

 8

16

1930-1960

16

1961

10

1962

  0

In February 1940 all members of the class were allocated to Nine Elms but many of them later moved to Eastleigh and Bournemouth.

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

Depot

1948 1955

1960

Bournemouth

10

  5

Eastleigh

  8

16

Nine Elms

  6

  3

16

16

16

Accidents and Incidents

  • One member of the Lord Nelson class was involved in what could have been a major accident on 23 January 1930. This entailed the leading driving wheels jumping off the track, though the locomotive ran for many yards before they re-railed themselves over a point.
  • 860 Lord Hawke was derailed at St. Denys, Hampshire on 14 August 1940 due to enemy action. A bomb fell on the track ahead of the train, which was unable to stop in time.
  • 852 Sir Walter Raleigh received a direct hit from an enemy bomb on 18 April 1941, and was so severely damaged that it was not returned to service until June 1942.
  • 854 Howard of Effingham suffered a firebox failure due to lack of water 23 April 1945, killing the fireman and injuring the driver.
  • 851 Sir Francis Drake was involved in a serious derailment at Byfleet in December 1946, due to the poor condition of the permanent way.
  • On 26 November 1947, 860 Lord Hawke was hauling a passenger train that was run into by another at Farnborough, Hampshire due to a signalman’s error. Two people were killed.
  • 30854 Howard of Effingham was hauling a passenger train that overran signals and was derailed by trap points at Shawford, Hampshire on 20 July 1952.

Preservation

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