Power Classification	4MT reclassified 4P5F in 1953
Introduced	1917 – 1934
Designer	Maunsell
Company	SECR/SR
Weight – Loco	61t 4cwt
Tender	39t 5cwt
Driving Wheels	5ft 6ins
Boiler Pressure	200psi superheated
Cylinders	Outside – 19in x 28in
Tractive Effort	26,035lbf
Valve Gear	Walschaert (piston valve)

Three factors dictated the type of locomotive that could run on the South Eastern and Chatham Railway (SECR): increased freight and passenger train loadings, poor track quality, and weak, lightly built bridges. An increasing number of passengers used the SECR to reach the cross-Channel ferries at Dover and Folkestone between 1910 and 1913, and heavy goods trains between Tonbridge and Hither Green marshalling yard stretched the capabilities of existing locomotives and infrastructure. On the lines of the former London, Chatham and Dover Railway (LCDR), flint beach pebbles on a bed of ash had been used for ballast. Conventional track ballast has irregular shapes that “lock” together to keep the track in place, whereas the smooth pebbles used by the LCDR failed to prevent track movement under strain. The economies in construction meant that only locomotives with low axle loadings could run safely on the track. These restrictions meant that the SECR was unable to follow a coherent locomotive strategy that reduced costs and increased serviceability. The railway’s Operating Department had to use mismatched classes of underpowered and obsolete 4-4-0 and 0-6-0 locomotives because they could run within the restrictions imposed by the infrastructure. This meant frequent double-heading that increased operational costs.

Maunsell was appointed CME of the SECR in 1913, following the retirement of Wainwright due to ill health. Wainwright left a legacy of competent but unspectacular locomotives that struggled to cope with the increased train lengths and loadings. Maunsell took control of the short-term situation by improving existing designs, and he introduced new engines to progressively replace obsolete classes. New designs could also cut costs on the SECR, as one capable mixed-traffic locomotive could undertake the work of two separate passenger or freight types.

In 1917 Maunsell produced his first new designs since he took over from Wainwright in 1913. He built a 2-6-0 tender engine number 810 (N class) and a corresponding 2-6-4T engine number 790 (K class – see under U class). They employed some GWR features such as taper boilers with high working pressure and long travel piston valves.

The N class was designed by Maunsell in 1914 to provide a sturdy mixed-traffic locomotive with high route availability. Intended to replace several obsolete 0-6-0 types, the N class was the first step in the SECR’s fleet standardisation programme, which also included the K class 2-6-4T passenger tank locomotive. Maunsell enlisted the help of former GWR engineer Holcroft, who suggested that a 2-6-0 wheel arrangement would allow the class to run on the poor-quality track in north Kent. This arrangement allowed for a longer wheelbase with leading axle to permit greater stability at speed on tight track curves, which had constrained the size of locomotives operating on the SECR. A longer locomotive could also accommodate a larger boiler than an 0-6-0, giving the N class sufficient power to avoid double-heading of locomotives on heavier trains.

The N class incorporated the principles of power and reliability established by Churchward on the GWR, using a Belpaire firebox that sloped downwards towards the cab instead of a round-topped version, a regulator located in the smokebox, long-travel valves for free running up to 70 mph, a sharply tapered and domeless boiler, and a right-hand driving position. These features are attributed to Holcroft, who worked on the GWR 4300 class before joining the SECR. The boiler was intended to become a standard component for use on future SECR locomotive designs, thereby reducing building times and improving organisation at the works. The size was constrained by the heavier axle-loading of Maunsell’s proposed 2-6-4 tank locomotive variant of the N class, the K class, and was consequently smaller than was otherwise possible on the 2-6-0 chassis. The need to reduce overall weight also meant that the latter would feature lightly braced frames.

Maunsell’s Chief Locomotive Draughtsman, Clayton, brought functional Midland Railway influences to the design, such as the shape of the cab and the drumhead-type smokebox, which sat on a saddle that was of wider diameter than the fully lagged and clad boiler. Clayton was also responsible for the tender and chimney designs. Snifting valves were provided to prevent vacuum formation in the cylinders when the locomotive was stationary, and the outside Walschaerts valve gear incorporated single slide-bars and piston tail rods. Innovations added by Maunsell’s team included steam-powered locomotive brakes, locating the boiler water top feed inside a dome-like cover with external clackboxes and water feed pipes mounted on either side, and a new type of superheater that segregated saturated and superheated steam. Maunsell also incorporated a screw reverser to control valve events, which was easier to maintain than the complex steam reverser configuration of previous SECR designs. All components were standardised for interchange with similar locomotive classes to ease maintenance and reduce production costs.

It is not surprising therefore that the N class locomotives bore some similarities to the GWR 4300 class. They also had a few Midland design features, such as the cabs and tenders. The original engine 31810 was built in 1917.

	GWR 4300 class Introduced by Churchward in 1911
	N class as introduced 1n 1917

After extensive trials with 31810 fifteen more engines were built in 1920-1922 (31811-31825). One of these (31822) was fitted with three cylinders and it was known as the N1 class.

The Ministry of Supply drew up a contract for a second batch to the same specification – to be built at the Royal Arsenal, Woolwich. The government backing came as part of a proposal to nationalise the railways, which would require a standard fleet of locomotives to promote economies in production and maintenance. The nationalisation proposal was abandoned; instead, the government passed the 1921 Railways Act, which grouped the railways into the “Big Four” in 1923. Building of the second batch went ahead to retain skilled labour at Woolwich as there was a decline in the requirement for armaments, but the fabrication of 119 boilers for allocation to the kits of parts was contracted-out because of limited production capacity at Woolwich and Ashford; the North British Locomotive Company built 85, Robert Stephenson and Company 20, and Kitson & Co. 14.

Unfortunately, building railway locomotives proved more tricky than putting guns together. Despite the help given by Ashford, the whole exercise ended in confusion. By 1924, the prefabricated components stored at Woolwich formed 100 complete N class kits for purchase from the government. The George Cohen and Armstrong Disposal Corporation was asked to take the 100 locos built at Woolwich onto their books for sale to any interested parties.

The Midland Great Western Railway of Ireland bought 12 kits prior to absorption by the Great Southern and Western Railway, which bought an extra 15. The latter 15 locomotives were divided into eight GSR Class 372 with 5-foot-6-inch driving wheels and six GSR Class 393 with 6 foot 0inch driving wheels: the final kit was kept for spares. The ones bought to run in Ireland were altered to run on the 5′ 3″ gauge there.

A further six were purchased by the Metropolitan Railway, which sent them to W.G. Armstrong Whitworth & Co. for conversion to class K 2-6-4 tank engines. Thereafter they worked principally goods services on the Metropolitan Railway.

The newly created Southern Railway, which had absorbed the SECR in the 1923 “Grouping”, undertook trials in the spring of 1924 to compare the performance of its freight locomotives. Because the Ns were designed to haul both freight and passenger traffic, Maunsell, as the newly appointed Chief Mechanical Engineer of the Southern Railway, decided to compare the design with the N1, LSWR S15 and LB&SCR K classes in trials that involved hauling trains of 65 loaded wagons. Although the S15 was superior in freight haulage capacity and operational economy, the N class’ good all-round performance on passenger and freight meant that the type was adopted as the company’s standard mixed-traffic design.

The Southern Railway subsequently bought fifty “Woolwich” kits for assembly at Ashford between June 1924 and August 1925. These were identical to the SECR batch and were given numbers in the series A826–A875. The fifty acquired by the Southern were variously distributed between the Eastern and Western sections. Those going West (where the influence of Ashford had not yet penetrated) soon gained a mournful reputation for multifarious failures, largely due to poor construction. The men bestowed on them the acid name of “Woolworths’. However, on the Eastern section section where they were also known as ‘mongolipers’.

The remaining 17 complete kits at Woolwich were bought by the Southern Railway, and formed the basis of later locomotive classes such as the three-cylinder SR W class 2-6-4 tank locomotive. The prototype W class was produced in 1932 from N class parts with the addition of water tanks, a coal bunker, a rear bogie and a third cylinder between the frames. Woolwich also stocked a surplus of N class bogie components, and these were bought by the Southern for rebuilding the LB&SCR E1 class 0-6-0 tanks into the E1R class 0-6-2 tanks.

The Metropolitan Railway bought six kits for conversion to the Metropolitan Railway K Class 2-6-4T tank engines, which were similar in outline to the SECR K class. The remaining 17 complete kits at Woolwich were bought by the Southern Railway, and formed the basis of later locomotive classes such as the three-cylinder SR W class 2-6-4 tank locomotive. The prototype W class was produced in 1932 from N class parts with the addition of water tanks, a coal bunker, a rear bogie and a third cylinder between the frames. Woolwich also stocked a surplus of N class bogie components, and these were bought by the Southern for rebuilding the LB&SCR E1 class 0-6-0 tanks into the E1R class 0-6-2 tanks.

In 1932, the Southern Railway ordered a final batch of 15 locomotives (1400–1414) to expand class availability on the Southern Railway’s network. These were built at Ashford works and differed from the previous 65 in a number of ways. The cabs of the final eight locomotives (1407–1414) were fitted for left-hand driving, which was adopted as standard by the Southern Railway. The original N class chimney was replaced with the lower-profile version used on the U1 class, which increased route availability by allowing the locomotives to pass under lower bridges and tunnels. Maunsell had begun to research smoke deflection techniques to improve driver visibility on the King Arthur class between 1926 and 1927, which resulted in the adoption of a standard smoke deflector design for the Southern Railway. A smaller version was fitted to 1400–1414 during building.

Before entering service, the batch was attached to 4,000-imperial-gallon tenders to increase operational range over the Southern Railway’s long Western section routes. Despite this advantage, tenders fitted to the eight left-hand drive examples were intended for use with right-hand drive locomotives. This resulted in the location of the fireman’s fittings on the “wrong” side of the cab. The design also necessitated the addition of a step to the footplate, as the boiler backhead was lower than the fall-plate that connected the tender and cab floors. The new batch incorporated a new set of footsteps beneath the front buffer beam, modified slide-bars and the dome was redesigned to incorporate the regulator to ease access during routine maintenance.

The N class was used to haul services over most of the SECR network and became a familiar sight on the difficult cross-country route between Tonbridge and Reading, on which the steep gradients had taxed the company’s 4-4-0 and 0-6-0 designs. The success of the 2-6-0 in traversing this route was due to their higher-capacity tapered boilers that produced an ample supply of steam, and the small 5 ft 6 in driving wheels that delivered considerable tractive effort when climbing gradients such as the 1 in 100 between Gomshall and Shalford.

After the grouping in 1923, the N class remained on the former SECR network, which was incorporated into the Southern Railway’s Eastern section. Typical services included Ramsgate, Ashford and Hither Green freights, and Cannon Street to Dover passenger trains. The spring of 1924 saw  A815 and A825 transferred to the former LSWR mainline between Waterloo and Guildford for trials. These proved successful, and paved the way for the allocation of most of the Woolwich batch to the Southern Railway’s Western section. The type regularly replaced Drummond’s ageing LSWR T9 class 4-4-0s on portions of the Atlantic Coast Express over the steeply graded mainlines west of Exeter.

The N class was also successful on the Central Section, where they worked alongside Billinton’s LB&SCR K class 2-6-0s. However the large cylinder and cab sizes of the N class prevented use of the type on the Eastern section’s Tonbridge–Hastings line. The route’s narrow bridges and tunnels were unable to accommodate the class, and provided justification for using the narrower 3-cylinder N1 class 2-6-0 on the route. Despite these restrictions, the class was capable of hauling heavy loads at moderate speeds, a useful attribute that was exploited throughout the Second World War. The entire class came into British Railways’ ownership in 1948 and could be seen in most areas of the Southern Region.

When introduced in 1917, the N class proved adept at hauling both passenger and freight services on the SECR. They were well liked by crews who appreciated the general robustness of the design, although the lightly built frames caused excessive vibration and rough riding on the footplate when worked hard. Despite there being little wrong with the original design, the N class’ full steaming potential was not realised because of the failure to capitalise upon a larger boiler, which was a direct consequence of Maunsell’s standardisation policy. Instead, the SECR batch was trial-fitted with stovepipe chimneys in an attempt to improve draughting. This was initially applied to 812 in 1921, although two more were fitted to 817 and 819 during building because of a shortage of chimneys at Ashford Works. The chimney fitted to 819 was transferred to 818 sometime between 1921 and 1924, though all stovepipes had been replaced with the standard N class type by April 1927. Another trial saw the addition of a second slidebar to 825, which gave better support to the valve gear and helped protect it from spillage from the driving wheel sander fillers.

The quality of the original design was such that No. A866 was put on display at the British Empire Exhibition at Wembley from May to November 1925, and no class-wide modifications were made until 1934. This was when the SECR and Woolwich batches began to receive new domes and front footsteps during overhauls and general repairs. These were the same design as those used on Nos. 1400–1414, and were intended to standardise components between the batches. The SECR and Woolwich batches also received smoke deflectors to prevent drifting smoke from obscuring the driver’s vision ahead. The U1 chimneys replaced the standard N class type on the earlier locomotives, which, along with the removal of the piston tail rods on the earlier batches, created a truly standardised appearance.

In 1937, Maunsell’s replacement Bulleid saw no need to improve draughting of the class, and spared them from trials with Lemaître multiple-jet blastpipes and wide-diameter chimneys. However, he had Maunsell’s smokebox-mounted anti-vacuum snifting valves removed at the end of the Second World War in an effort to reduce maintenance. Bulleid also had eight new 4,000-imperial-gallon tenders built specially for the left-hand drive locomotives. In 1947, 1831 was given electric lighting and converted to oil-burning as part of government-backed fuel trials in anticipation of a post-war coal shortage, though it was reverted to coal-firing in December 1948.

The class was heavily used by British Railways: 29 locomotives required replacement cylinders between 1955 and 1961 due to excessive wear. Frames were occasionally replaced due to stress caused by heavy use, and the steam circuit was revised when new cylinders were fitted: the inside steam pipes of Maunsell’s original design were replaced by outside steam pipes emerging from the smokebox, behind the smoke deflectors. From 1957, some of the locomotives had larger-diameter BR Standard Class 4 chimneys fitted to improve draughting with poor-quality coal, though the decline of steam on the Southern Region precluded use on the entire class. Crew reports maintained that the latter modifications cut fuel and water consumption. The final set of modifications constituted the fitting of new injectors and Automatic Warning System (AWS) equipment in 1957 and 1959 respectively.

Although sufficient for the Southern Railway’s needs, the N class was an ideal test-bed for experiments with new steam technology. The first experiment entailed fitting a Worthington feed pump to A819 in 1924. The trial was moderately successful, and the pump remained in use until removal in 1927. In June 1930, A816 was withdrawn from service for the application of experimental Anderson steam conservation equipment at Eastleigh Works. This was designed by a Scottish marine draughtsman who proposed the use of a fan system to condense spent steam and improve draughting of the fire on long-distance runs in regions with poor access to water.

A816 emerged from Eastleigh in August 1931 for trials, but was stopped when temperature variations within the condensing equipment caused water leakage. Modifications were made to improve the draughting of the locomotive, incorporating a box-like chimney attached to the condenser array by pipes. A816 was released for more trials, and produced performances well-below those displayed by the unmodified members of the class. The experiment was ended when the system’s developers ran out of money, and the locomotive was converted back to standard form between May and August 1935, re-entering service as 1816.

The final experiment with performance enhancement began in October 1933, when 1850 had its Walschaerts valve gear replaced with Marshall valve gear at Eastleigh Works. The engine was trialled on the Western section, where the gear showed promise at slower speeds, with reduced consumption of coal and water. Problems were encountered at speeds over 50 mph, at which a severe knocking sound was reported by the footplate crew. When trialled on a Basingstoke–Waterloo semi-fast (a high-speed passenger train that stops at selected intermediate stations), the valve gear disintegrated near Woking. After immediate withdrawal from traffic, the locomotive had its Walschaerts valve gear re-fitted and 1850 re-entered traffic in April 1934.

Suitable work for the class began to decline after completion of the Kent Coast route electrification in 1959. The reduction of work precipitated a phased reduction of the class that began with the withdrawal of 31409 in 1962. The withdrawal programme intensified after boundary changes on the Southern Region placed the lines west of Salisbury under Western Region control in 1963. Class members based at Exmouth Junction shed were withdrawn in 1964, whilst the Southern Region’s allocation was gradually replaced by Bulleid’s Light Pacifics. The last operational members of the class were 31405 and 31408; both were withdrawn in 1966.

31831 was converted to oil burning during the coal crisis after the Second World Was but was later converted back to coal burning.

Number in Service.

	Built		Withdrawals	No. in Service
	BR Numbers	Quantity
1917	31810	1		1
1920	31811 – 15	5		6
1922	31816 – 21	6		12
1923	31823 – 24	2		14
1924	31825 – 46	22		36
1925	31847 – 75	29		65
1932	31400 – 5	6		71
1933	31406 – 12	7		78
1934	31413 – 14	2		80
1935-61				80
1962	31409 & 31414		2	78
1963			25	53
1964			41	12
1965			6	6
1966			6	0

• 31822 built in 1923 had three cylinders and was considered to be N1 class.
• The last 6 (31405, 31408, 31411, 31816, 31866 & 31873) locomotives in service were all withdrawn from service at Guildford in 1966.

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

Depot	1948	1955	1960
Ashford	5	8	12
Barnstable		2
Bricklayers Arms	4	15	10
Dover Marine	4	4	7
Eastleigh	5
Exmouth Junction	20	18	21
Faversham		2
Fratton	1
Gillingham	4	2	1
Guildford			3
Hither Green		8	5
Norwood Junction	2
Reading South	6
Redhill	12	10	16
Salisbury	4	2	2
Stewarts L:ane	10	9	3
Tonbridge	3
	80	80	80

Accidents and Incidents

• On the 2nd September 1945 locomotive 1811 (31811) was hauling an empty stock train of 13 coaches from Streatham to Newhaven when it ran into buffers at Haywards Heath. The train should have come to a stand in the down sidings, prior to reversing across the up line, over which single line working was in operation. The train failed to stop and collided at high speed with the buffer stops at the end of the siding and the with the face wall of the tunnel portal immediately beyond the buffers. The front of the engine overrode the buffer stops and the filling behind them until the engine buffers struck the brickwork of the tunnel portal, becoming embedded to a depth of about a foot. The trailing end of the tender was lifted by the momentum of the coaches behind it and both bogies of the leading coach and the leading bogie of the second coach were piled underneath the tender.Both the driver and fireman were killed and the guard suffered bruises and shock.
• In April 1958 31867 was hauling a parcels train that overran signals and collided with an electric multiple unit at Gloucester Road Junction, Croydon. Nine people were injured.

Preservation

• 31874 (SR A874, SR 1874 & BR 31874)

Back to SR

Back to Locomotives