similar in appearance to those used on the H15s, although strengthened during construction with extra internal bracing to hold of water. A shortage of copper delayed completion of Nos. 741–745, and the last of the batch emerged from Eastleigh in November 1919. After the running-in of Nos. 736–745 and an intensification of the LSWR timetable to the West Country, a second batch of ten was ordered in October 1921. They entered service over the period June 1922 – March 1923, and were numbered in the series 746–755. At "Grouping" in January 1923, the LSWR became part of the new Southern Railway, whose Chief Mechanical Engineer was Richard Maunsell. Maunsell planned to introduce his own designs of express passenger locomotive, one of which was to become the future Lord Nelson class. Despite this, there was a short-term need to maintain existing services that required modification and expansion of Urie's N15 design. Maunsell’s "Eastleigh Arthurs": Drummond rebuilds Maunsell's projected design of express passenger locomotive was not ready for introduction during the summer timetable of 1925, so a third batch of ten N15s was ordered for construction at Eastleigh. This batch was part of an outstanding LSWR order to rebuild 15 of Drummond's unsuccessful 4-cylinder F13, G14 and P14 classes 4-6-0s into 2–cylinder H15 class locomotives. Only the five F13s were converted to H15s; the remaining ten G14 and P14s (Nos. 448–457, renumbered E448–E457) were rebuilt as N15s, implementing modifications to Urie's original design. The modifications are attributed to Maunsell's Chief Draughtsman James Clayton, who had transferred to Ashford railway works in 1914 from Derby works. They were the result of cooperation between the South Eastern and Chatham Railway (SECR) and the Great Western Railway (GWR) when Maunsell was seconded to the Railway Executive Committee during the First World War. The aim was to create a series of standard freight and passenger locomotives for use throughout Britain, and meant that Clayton was privy to the latest GWR developments in steam design. These included streamlined steam passages, long-travel valves, the maximisation of power through reduced cylinder sizes and higher boiler pressure. Maunsell initiated trials with Urie N15 No. 442 in 1924, and proved that better performance could be obtained by altering the steam circuit, valve travel and draughting arrangements. As a result, Clayton reduced the N15 cylinder diameter to and replaced the safety valves with Ross pop valves set to boiler pressure. The Urie