SR N1 Class

The SR N1 Class was a series of six three-cylinder 2-6-0 Mogul mixed-traffic locomotives designed by Richard Maunsell and introduced on the South Eastern and Chatham Railway in 1922, representing a three-cylinder development of the highly successful N Class 2-6-0 that Maunsell had introduced in 1917. Where the standard N Class used two outside cylinders with Walschaerts valve gear, the N1 Class applied three cylinders — two outside and one inside — with Gresley's conjugated valve gear for the inside cylinder, producing smoother power delivery and slightly better performance on the sustained gradient climbing of the SR's more demanding routes.

Maunsell designed the N1 in collaboration with Gresley of the Great Northern Railway, with the two CMEs sharing technical knowledge during the difficult wartime and immediate post-war period when locomotive development resources were constrained. The Gresley conjugated valve gear applied to the inside cylinder of the N1 was the same system that Gresley was simultaneously developing for his own GNR Pacifics, and the N1 and related three-cylinder types represented a productive exchange of engineering knowledge between the two railways.

In service the N1 Class gave competent performance on SR mixed-traffic duties, though the three-cylinder layout proved more demanding to maintain than the simpler two-cylinder N Class, and the relative complexity of the conjugated valve gear required careful attention from depot fitters. Only six were built — the SR ultimately decided that the performance advantage over the N Class did not justify the additional maintenance — and the N1 remained a small class. None was preserved, though the N Class that the N1 developed from is represented by several preserved examples including No. 31874 at the Mid-Hants Railway.