LSWR N15 class
The LSWR N15 class is a British 2–cylinder 4-6-0 express passenger steam locomotive designed by Robert Urie. The class has a complex build history spanning three sub-classes and ten years of construction from 1918 to 1927. The first batch of the class was constructed for the London and South Western Railway, where they hauled heavy express passenger 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.
Following the grouping of railway companies in 1923, the LSWR became part of the Southern Railway 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 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 Works and the North British Locomotive Company in 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 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 ports of Portsmouth, Weymouth and Southampton had been increasing prior to the war, and was beginning to overcome the capabilities of the LSWR's passenger locomotive fleet. His response was to produce a modern, standard express passenger design similar to the H15.
Design and construction
Trials undertaken in 1914 with the H15 class prototype had demonstrated to Urie that the basic design showed considerable speed potential on the Western section of the LSWR from Basingstoke westwards, and could form the basis of a powerful new class of 4-6-0 express passenger locomotive with larger driving wheels. The LSWR required such a locomotive, which would need to cope with increasing train loads on this long and arduous route to the West Country. The result was the N15 class design, completed by Urie in 1917. It incorporated features from the H15 class, including eight-wheel double bogie tenders with outside plate frames over the wheels and exposed Walschaerts valve gear. High running plates along the boiler were retained for ease of oiling and maintenance.Despite the similarities, the N15 class represented a refinement of the H15 template. The cylinders were increased in size to in diameter, the largest used on a British steam locomotive at that time. The substantial boiler design was also different from the parallel version used on the H15, and became the first tapered types to be constructed at Eastleigh Works. Contrary to boiler construction practices elsewhere where tapering began near the firebox, it was restricted to the front end of the N15's barrel to reduce the diameter of the smokebox, and consequently the weight carried by the front bogie. The design also featured Urie's design of narrow-diameter "stovepipe" chimney, a large dome cover on top of the boiler, and his "Eastleigh" superheater.
"Urie N15s"
The N15 design was approved by the LSWR management committee, though the order for construction was postponed until wartime control of raw materials was relaxed. Government approval was obtained in mid–1918, and Eastleigh Works began to produce the LSWR's first new locomotive class since 1914.The first locomotives, later known by crewmen as the "Urie N15s", were built in two ten-engine batches by the LSWR's Eastleigh Works between 1918–19 and 1922–23. Of the first batch, the prototype, No. 736 entered service on 31 August 1918, with four more appearing between September 1918 and April 1919. They shared a similar profile to Urie's H15 class with the use of flat-sided Drummond-style cabs with gently curving roofs. The double bogie tenders were outwardly 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 10 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 10 G14 and P14s classes 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 and the Great Western Railway 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 boiler was retained, though the Eastleigh superheater was replaced by a Maunsell type with 10 per cent greater superheating surface area. This was supplemented by a larger steam chest and an increased-diameter chimney casting specially designed for the rebuilds. It incorporated a rim and capuchon to control exhaust flow into the atmosphere. Valve events were also revised to promote efficient steam usage and the wheels were re-balanced to reduce hammerblow.
When rebuilding was complete, only the numbers, smokebox doors with centre tightening handles and the flat-sided cabs remained of the G14 and P14 classes. The rebuilds retained their distinctive Drummond "watercart" tenders, which were modified with the removal of the complex injector feedwater heating equipment. The "watercart" tenders were of water and coal capacity. The 10 rebuilds became the first members of the King Arthur class upon entering service.
"Scotch Arthurs"
As the Drummond G14 and P14 4-6-0s were rebuilt to the N15 specification at Eastleigh, a lack of production capacity due to repair and overhaul meant that Maunsell ordered a further batch of 20 locomotives from the North British Locomotive Company in 1924. The company had under-quoted to gain the contract, which meant that production of the batch was rushed. The necessity to maintain an intensive timetable on the Southern Railway's Western section prompted an increase of the order to 30 locomotives. Their construction in Glasgow would gain them the "Scotch Arthurs" nickname in service. They were all delivered to the Southern Railway by October 1925, and featured the front-end refinements used on the Drummond rebuilds.The North British batch was built to the Southern's new composite loading gauge and differed from previous batches in having an Ashford-style cab based upon that used on the N class. Unlike the Drummond cab retained by Nos. 448–457 and E741–E755, the Ashford cab was of an all-steel construction and had a roof that was flush with the cab sides, allowing it to be used on gauge-restricted routes in the east of the network. It was inspired by the standard cab developed in 1904 by R. M. Deeley for the Midland Railway, and was one of a number of Midland features introduced by Clayton to the SECR and subsequently the Southern Railway. The smokebox door was revised to the Ashford pattern, which omitted the use of central tightening handles in favour of clamps around the circumference. The batch was fitted with the Urie-designed, North British-built capacity double-bogie tenders.