 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.