 The Southern Railway was primarily a passenger-carrying railway which used most of its resources to extend its electrified lines.There was a continuing need for steam freight locomotives however, although the Traffic Department preferred mixed traffic designs which could also haul passenger trains on the remaining non-electrified lines at peak periods.By the late 1930s the Southern Railway was adequately served with powerful mixed traffic locomotives of the S15 and N and N1 classes, but there was a need for a smaller freight locomotive with high route availability that could also undertake light passenger duties.