 The N class incorporated the principles of power and reliability established by George Churchward, using a Belpaire firebox that sloped downwards towards the cab instead of a round-topped version, a regulator located in the smokebox, long-travel valves for free running up to , a sharply tapered and domeless boiler, and a right-hand driving position.These features are attributed to Holcroft, who worked on the GWR 4300 class before joining the SECR.The boiler was intended to become a standard component for use on future SECR locomotive designs, thereby reducing building times and improving organisation at the works.