Британские паровозы LSWR N15: "Король Артур" и его модификации.

Class of 74 two cylinder 4 6 0 locomotives

The LSWR N15 class was 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 (LSWR), 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 (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 Works 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.

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 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.

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. Of the first batch, the prototype, No. 736 entered service on 31 August 1918, with four more appearing between September 1918 and April 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. Despite this, there was a short term need to maintain existing services that required modification and expansion of Urie's N15 design. The Urie boiler was retained, though the Eastleigh superheater was replaced by a Maunsell type with 10 per cent greater superheating surface area. 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.

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. After the first 14 (Nos. E793–E806) were built, it was decided to discontinue construction in favour of Maunsell's new 4 cylinder Lord Nelson class design in June 1926. This was because the tenders attached to Nos. E763–E772 were better suited to the longer routes of the Western section. After the order was changed to the Lord Nelson class design, 14 N class tenders were fitted to Nos. E793–E806 for use the Central section.

The N15 class was intended to haul heavy expresses over the long LSWR mainlines between Waterloo, Weymouth, Exeter and Plymouth. The Southern Railway's motive power re organisation following the Grouping of 1923 saw the class allocated to sheds across the network and used on Bournemouth to Oxford cross country trains. Operations were expanded to more restricted Central and Eastern section mainlines in 1925, and suitably modified class members hauled commuter and heavy boat trains from London Victoria to Dover Marine and expresses to Brighton. In 1931, No. E780 Sir Persant hauled the inaugural Bournemouth Belle Pullman train from Waterloo to Bournemouth West. In peacetime, the class was occasionally used on fast freights from Southampton Docks, although it was common to see them at the head of freight and troop trains during the Second World War. Ten "Urie Arthurs" were transferred to the London and North Eastern Railway (LNER) in October 1942, and were based at Heaton shed for use on freight and occasional passenger trains in the north east and southern Scotland. They returned to the Southern Railway in July 1943 after the introduction of United States Army Transportation Corps S160 class 2 8 0s into service.

In 1940, No. 751 Etarre, No. 755 The Red Knight, No. 775 Sir Agravaine, and No. 776 Sir Galagars along with T14 No. 458 and N15X No. 2328 Hackworth suffered bomb damage during the air raid on Nine Elms shed. No. 458 was scrapped and the other engines were eventually repaired. On 16 August 1944, 806 Sir Galleron was damaged by a V 1 flying bomb whilst pulling a passenger train in Upchurch; eight people were killed. The locomotive was eventually repaired and put back into service. On 26 November 1947, locomotive No. 753 King Arthur was hauling a passenger train that was in a rear end collision with another, the other being hauled by SR Lord Nelson Class 4 6 0 No. 860 Lord Hawke, at , Hampshire due to a signalman's error. Two people were killed. On 22 January 1955, locomotive No. 30783 Sir Gillemere collided with H15 No. 30485 at Bournemouth Central station after its driver misread signals. The locomotive was subsequently repaired; The H15 was condemned. On 18 September 1962, locomotive No. 30770 Sir Prianus was hauling a newspaper train that caught fire between Knowle Junction and Four of the five carriages were destroyed.

Under LSWR ownership, the "Urie N15s" were painted in Urie's LSWR sage green livery for passenger locomotives. This was distinct from Drummond's sage green because it was more olive in colour, and yellowed with cleaning and weathering. The first Southern livery continued that of the LSWR, though with primrose yellow transfers showing "SOUTHERN" and the locomotive number, placed on the tender. However, from 1942 to 1946, during the Second World War and its aftermath, members of the class under overhaul were turned out in unlined black livery as a wartime economy measure, with green shaded sunshine yellow lettering.

British Railways gave the class the power classification of 5P after nationalisation in 1948. For the first 18 months the locomotives sported a transitional livery: Southern Railway malachite green with "BRITISH RAILWAYS" on the tender in sunshine yellow lettering. As each member of the class became due for a heavy general overhaul, they were repainted in the new standard British Railways express passenger livery of Brunswick green with orange and black lining from April 1949.

Hornby Railways manufacture a model of the N15 in OO gauge.