SECR N1 Class - Background

Background

Richard Maunsell's N class mixed-traffic 2-6-0 prototype for the South Eastern and Chatham Railway (SECR) was completed in 1917. It showed a marked improvement in performance over his predecessor Harry Wainwright's 0-6-0 and 4-4-0 designs when tested on freight and local passenger trains. The success of the prototype encouraged the SECR management to order a batch of 15 in 1919 after government restrictions regulating locomotive production during the First World War were relaxed. Ashford locomotive works was already committed to undertaking deferred repair work however, which temporarily slowed construction of new locomotives. This resulted in the gradual completion of the 1919 N class order as works capacity permitted between 1920 and 1923.

Operational experience with the N class prototype demonstrated that it was capable of coping with peacetime passenger and freight traffic on the mainline between London and Ramsgate, but Maunsell anticipated an increase in traffic that would require a more powerful locomotive capable of hauling longer trains. The use of larger engines was prevented by low permitted axle loadings on parts of the SECR network, caused by economies in track construction by using flint beach pebbles as track ballast; this material failed to hold the track in place when under strain and could not support heavy locomotives. In the meantime Maunsell settled upon producing a 3-cylinder version of the N class 2-6-0, which provided the opportunity to test a variant of the Gresley conjugated valve gear developed by his assistant, Harold Holcroft.