In extended trials the design proved to be so successful that following abortive attempts by the Association of Railway Locomotive Engineers to produce standard loco classes for use by all British railway companies, the government adopted the standards idea and selected the type to be produced by the former munitions factory at the Woolwich Arsenal as an alternative to closing the factory once it's wartime function was no longer required.

Ashford works themselves did not move quickly producing the class, with only 15 locos emerging (up to 825) until December 1923 - number 822, was built as the prototype three cylindered version to be known as the N1 class.

Meanwhile the Woolwich Arsenal produced kits of parts, however after the government abandoned its attempt to nationalise the railways there were few takers (the nationalised railway was due to receive 100 of the class). Those companies which did buy the "kits" were the G.S.& W.R. of Ireland (Maunsell's native railway) , the Metropolitan Railway, and the newly formed Southern Railway which seized the opportunity to pick up the parts for 50 engines at a bargain price. These 50 were assembled at Ashford, were numbered A826 to A875 in the Southern list, and this sub-class of the Ns was nicknamed by their footplatemen "Woolworths" (a contortion of Woolwich). N°A866 was put on display at the British Empire Exhibition at Wembley from May to November 1925, as Southern Railway N°866.

The first 65 of the class were built with the standard SECR right hand drive, however a further 15 engines numbered 1400 to 1414 were built between 1932 and 1934, with U1 Chimneys and domes (U1 domes were lower), 4000 gallon tenders with a step in their footplate, and some of this batch had the by-then Southern standard left hand drive (note that in written accounts the number of locos which received left hand drive differs between authors, so as always work from a good photograph if you want an accurate model).

Changes to details and modifications happened throughout the class' lifetime. Some of the most pertinent points have been summarised by SREmG member Tony Harker:

• Stovepipe chimneys were fitted to 812 in 1921 and to 817 & 819 when built. 818 received the stovepipe chimney from 819 sometime before 1923. Later, about 1926/7, they were replaced by parallel types.
• Immediately after the Grouping all locos were painted sage green, (Urie LSWR Green) repainted into (Maunsell) olive after 1931.
• During 1939, 1413 & 1850 were painted Olive green with no lining. Others were painted black but only when necessary, i.e. after a major overhaul, etc.
• Between 1939 and 1941 1821/25/47/78 & 1403 were painted Maunsell Green with Bulleid gilt lettering unlined. Two engines received Malachite green in 1946, 1817 & 1854. Lining was yellow edged in black with "Sunshine" style lettering, not gilt.
• All Ns were painted black by the end of the war. It is not known if Bulleid or Maunsell style lettering was applied in general to wartime liveried Ns, but 1831 carried Bullied style (this loco was converted to oil burning during 1947 and converted back in 1948).
• When built all engines had smokebox mounted snifting valves. These were removed during the war or just after.
• Engines built before 1930 had piston tail rods - these were removed in 1933 when front steps were fitted. Engines built by the SR, i.e. 1400 and later, had front steps from new.
• Some locos ran with tail rods and front steps for a while, e.g. 1824.
• In 1933, experimental Marshall valve gear and motion was fitted to 1850. It was found to be unsuccessful and removed in April 1934 after the loco failed.
• Two types of smoke deflector were fitted to the class in 1933, some had a vertical handrail with a round handhole, but most had a horizontal handrail with a rectangular handhole.
• In 1930/31 A816 was extensively modified with a steam condensing apparatus for trial. This trial lasted until mid 1935 when it was rebuilt into "normal" N at Eastleigh so it will have been re-painted in dark olive. It's chimney was replaced by a U1 type.
• From 1955 until 1961, 29 engines were re-cylindered. In some cases the frames were replaced but others only had the front end renewed. Outside steampipes were fitted for the new cylinders. Some engines, e.g. 31848, ran for a while with the smoke deflectors removed. From 1957 some locos received BR Class 4 chimneys, e.g. 31412 which had a new chimney (but not new cylinders).
• Steam Heating hoses were removed during the Summer and were sent to Eastleigh for testing! Was this general for all SR locos?

The N Class was a reliable locomotive used throughout the SR network over a wide range of duties from semi fast passenger duties to pick-up goods. Their high capacity boilers, small coupled wheels, and free steaming characteristics delivered considerable traffic effort that was much in evidence when the class excelled itself hauling heavy loads during World War Two. The class migrated from the SR Eastern section to work additionally on the Central and Western sections, and in their latter BR(S) days continued to excel on passenger and goods duties in the West Country. Withdrawals were between 1962 to 1966.

Drawings of the N Class are in "Southern Locomotives to Scale" by Ian Beattie, pub. D. Bradford Barton, ISBN 0 85153 389 2, but these are not accurately to 4mm scale (1/76), and the March 1996 edition of Railway Modeller page 119 which are more accurate. Weight diagrams are available in "Maunsell Locomotives" by Brian Haresnape , ISBN 0 7110 0734 8 and "A Pictorial Record of Southern Locomotives" by JH Russell Published by BCA/OPC (no ISBN given). These drawings are near enough to scale. No detailing is shown however.

Close relatives of the N Class were the 3 cylinder version N1 Class, the ill-fated K Class 2-6-4T "River" tanks (which were contemporaries of the N), and the U and U1 classes.