LSWR N15 class

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 1919 to 1926. 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 express passenger locomotives in the Southern Railway.

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.