When the South Eastern & Chatham needed new suburban tank locomotives for the south of London, Harry Wainwright used the existing 0-4-4T locomotives of the SECR's constituents as an inspiration. These were the SER's class Q and the LCDR's classes R and R1. To be specific, he used the R1 as basis for the development of the new class H.

Between 1904 and 1909, 64 were built by Ashford Works. After it was realized that actually two more had been ordered and only their parts manufactured, these two were completed in 1915. Most were used on ex-SER lines and only the 13 which were used on ex-LCDR lines had an additional Westinghouse brake. The boiler designed for the class H was later also used for rebuilding other classes.

All went to the Southern Railway and all but two were taken over by British Railways in 1948. In the following years, many of them were equipped for push-pull service and used on rural branch lines. Between 1952 and 1964, 64 were withdrawn. 31263, the last one to be withdrawn, was preserved and is owned by the Bluebell Railway since 2008, now in SECR livery and carrying the number 263.

Shortly before the First World War, the SECR had the problem that the significantly increased traffic volumes were offset by the weak, outdated locomotives and the light rails and bridges. On the one hand passenger trains had to be transported between London and the port of Dover and on the other hand ever heavier goods trains had to be transported. For cost and time reasons, a locomotive had to be developed for both tasks.

Maunsell found the help of Harold Holcroft, a former GWR employee. Since the wheel arrangement 2-6-0 was selected for the task, the GWR class 4300, on which Holcroft had worked, was used as the basis. Thus, the locomotive also contained principles that Churchward had worked out. Visual influences, on the other hand, came from the Midland Railway, which had been brought in by the chief draftsman James Clayton.

Some assemblies were developed in such a way that they could also be used on other locomotives. There were more similarities with the class K tank locomotive, which had the wheel arrangement 2-6-4T. Since the same boiler was to be used on both locomotives and the supplies had to be carried on the tender locomotive, the boiler could not be too heavy to maintain the axle load. The frame also had to be built relatively lightly.

As a result, the potential of the tender locomotive was not fully exploited. This boiler had a Belpaire firebox that narrowed towards the bottom and a boiler barrel that tapered towards the front. The valves were designed with a long travel to allow speeds of up to 70 mph (113 km/h).

As production was delayed due to the First World War, the first locomotive was only completed in 1917. The first series of 15 locomotives was only delivered between 1920 and 1923. One of these was rebuilt with three smaller cylinders, serving as a prototype for the N1 class.

No. 1850 with smoke deflectors and Marshall valve gear in February 1934 at Eastleigh

National Railway Museum

When the railway companies were grouped, Maunsell had the task of selecting a locomotive from the predecessor companies for mixed service. As the Class N was a good all-rounder it was chosen and 100 kits were made at the Royal Arsenal in Woolwich. 50 of these were assembled for the SECR at Ashford and the remainder were sold to other railway companies. Hence the nickname “Woolworths”.

In the years that followed, some locomotives were used to test different upgrades, but these were not adopted in the entire class. The last 15 locos were built directly by Southern Railway in Ashford. The last eight of them had the driver's position on the left and smoke deflectors. The previous locomotives could not be used on all lines of the Southern because the cylinders, the chimney and the cab exceeded the loading gauge in some places. While the outer dimensions of the cylinders could not be reduced, these last locomotives were given a lower chimney.

Some of the older locomotives were subsequently adapted to the last ones built. All 80 went to British Railways in 1948 and not one was retired before 1962. Some had received new cylinders or frames during this time. New chimneys were also installed for better draft. It was not until 1966 that the last six members of the class N disappeared from service. Number 31874 was rescued from a junkyard in 1974. Since 2014, its overhaul has been taking place.

D1 No. 494 with Belpaire firebox

Locomotive Magazine, January 1922

The Class D express locomotives were among Wainwright's first designs for the SE&CR. They were brightly colored to attract more public attention. They were built by different manufacturers, from 1905 also with Belpaire fireboxes. From 1913 Maunsell rebuilt some machines into the heavier class D1, which also had a Belpaire firebox. From around 1920, most of them received a superheater. A larger number of withdrawals took place from 1951 and the last rebuilt class D1 locomotives disappeared in 1961.