Based around a design of R.W. Urie from 1918 for an express passenger class of 4-6-0s, the 'King Arthur' or 'N15' class eventually totalled around 74 locomotives. The original 20 locomotives built to Urie's design were, however, not successful and when Maunsell was faced by the necessity, soon after the Grouping of 1923, to construct further express locomotives he took the opportunity to modify the original design and alongside the new build locomotives, also modified the original 20. Successful after the modifications, the career of the class on both the Central and Eastern sections of the SR was curtailed by the SR's policy of main line electrification, but the type continued to offer sterling services on the ex-LSWR main lines until the arrival of the Bulleid Pacifics. Peter Swift provides a reference to the class with detailed 4mm scale drawings along with a comprehensive selection of colour and mono photographs that illlustrate the considerable variety of liveries carried by the locomotives during their careeers and the detail differences that marked out each individual locomotive at particular dates. The locomotives were built at Eastleigh and by North British in Glasgow. As express passenger locomotives, examples of the class operated widely over the Southern Railway and latterly Southern Region. One example, No 30777, survives in preservation as part of the National Collection.