[4] 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.

[5] 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.

[9] 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.

[5] Maunsell took control of the short-term situation by improving existing designs, and he introduced new engines to progressively replace obsolete classes.

[11] 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.

[12] Maunsell enlisted the help of former GWR engineer Harold Holcroft, who suggested that a 2-6-0 wheel arrangement would allow the class to run on the poor-quality track in north Kent.

[2] 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.

[12] The N class incorporated the principles of power and reliability established by George Churchward, 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 (110 km/h), a sharply tapered and domeless boiler, and a right-hand driving position.

[13] 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.

[14] Maunsell's Chief Locomotive Draughtsman, James 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.

[15] The first left Ashford Works in June 1920, featuring a greater superheating surface area within the boiler as a result of operational experience with No. 810.

[15] 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 newly created Southern Railway, which had absorbed the SECR in the 1923 "Grouping", undertook trials in early 1924 to compare the performance of its freight locomotives.

[22] Before entering service, the batch was attached to 4,000-imperial-gallon (18,184 L) tenders to increase operational range over the Southern Railway's long Western section routes.

[22] 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.

[25] 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.

[10] 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 (1.68 m) driving wheels that delivered considerable tractive effort when climbing gradients such as the 1 in 100 between Gomshall and Shalford.

[15] Typical services included Ramsgate, Ashford and Hither Green freights, and Cannon Street to Dover passenger trains.

[15] The type regularly replaced Dugald Drummond's ageing LSWR T9 class 4-4-0s on portions of the Atlantic Coast Express over the steeply graded mainlines west of Exeter.

[15] 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.

[14] 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.

[27] In 1937, Maunsell's replacement Oliver Bulleid saw no need to improve draughting of the class, and spared them from trials with Lemaître multiple-jet blastpipes and wide-diameter chimneys.

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.

Anderson, 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.

[32] 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 No. 1816.

[36] The engine was trialled on the Western section, where the gear showed promise at slower speeds, with reduced consumption of coal and water.

[29] 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.

[4] 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.

[15] From 1925, the class was repainted in a darker olive green livery, introduced by Maunsell, with plain white lining, black borders and primrose yellow markings.