The newly created Southern Railway, which had absorbed the SECR in the 1923 "Grouping", undertook trials in early 1924 to compare the performance of its freight locomotives. Because the Ns were designed to haul both freight and passenger traffic, Maunsell, as the newly appointed Chief Mechanical Engineer of the Southern Railway, decided to compare the design with the N1, LSWR S15 and LB&SCR K classes in trials that involved hauling trains of 65 loaded wagons. Although the S15 was superior in freight haulage capacity and operational economy, the N class’ good all-round performance on passenger and freight meant that the type was adopted as the company's standard mixed-traffic design. The Southern Railway subsequently bought fifty "Woolwich" kits for assembly at Ashford between June 1924 and August 1925. These were identical to the SECR batch and were given numbers in the series A826–A875. The Midland Great Western Railway of Ireland bought 12 kits prior to its amalgamation into the Great Southern Railways, which bought an extra 15. The latter 15 locomotives were divided into eight GSR Class 372 with driving wheels and six GSR Class 393 with driving wheels: the final kit was kept for spares.