 To mitigate this, a wider-diameter blastpipe was cast for the locomotive and a new smokebox fabricated to accommodate a wide-diameter cast chimney.The rest of the construction process followed the 1919 N1 specification, and the final three members of the order for 15 N class locomotives were built as intended.The N1 prototype was completed in December 1922 and attached to a standard Maunsell flat-sided Ashford N class tender.