The LSWR N15 class was a British 2–cylinder 4-6-0 express passenger steam locomotive designed by Robert W. Urie. The class has a complex build history spanning three sub-classes and eight years of construction from 1918 to 1927. The first batch of the class was constructed for the London and South Western Railway (LSWR), where they hauled heavy express trains to the south coast ports and further west to Exeter. After the Lord Nelsons, they were the second biggest 4-6-0 passenger locomotives on the Southern Railway. They could reach speeds of up to 90 mph (145 km/h). Following the grouping of railway companies in 1923, the LSWR became part of the Southern Railway (SR) and its publicity department gave the N15 locomotives names associated with Arthurian legend; the class hence becoming known as King Arthurs. The Chief Mechanical Engineer (CME) of the newly formed company, Richard Maunsell, modified the Urie locomotives in the light of operational experience and increased the class strength to 74 locomotives. Maunsell and his Chief Draughtsman James Clayton incorporated several improvements, notably to the steam circuit and valve gear. The new locomotives were built over several batches at Eastleigh and Glasgow, leading to the nicknames of "Eastleigh Arthurs", "Scotch Arthurs" and Scotchmen in service. The class was subjected to smoke deflection experiments in 1926, becoming the first British class of steam locomotive to be fitted with smoke deflectors. Maunsell's successor, Oliver Bulleid, attempted to improve performance by altering exhaust arrangements. The locomotives continued operating with British Railways (BR) until the end of 1962. One example, SR N15 class 777 Sir Lamiel, is preserved as part of the National Collection and can be seen on mainline railtours. Background Robert Urie completed his H15 class mixed-traffic 4-6-0 design in 1913 and the prototype was built in August 1914. It showed a marked improvement in performance over Dugald Drummond’s LSWR T14 class 4-6-0 when tested on local and express passenger trains. The introduction of ten H15 engines into service coincided with the outbreak of the First World War, which prevented construction of further class members. Despite the interruption caused by the conflict, Urie anticipated that peacetime increases in passenger traffic would necessitate longer trains from London to the south-west of England. Passenger loadings on the heavy boat trains to the London and South Western Railway’s (LSWR) ports of Portsmouth, Weymouth and Southampton had been increasing prior to the war, and