LSWR Class N15

LSWR N15 class SR King Arthur class
30783 Sir Gillemere at Eastleigh, 1950. Note the "Cycling Lion" crest on the eight-wheel bogie tender
Type and origin Power type Steam Designer Robert Urie Richard Maunsell (redesign) Oliver Bulleid (modifications) Builder SR Eastleigh Works (44) North British Locomotive Co. (30) Build date 1919–1926 Total produced 74
Specifications Configuration: ​  • Whyte 4-6-0  • UIC 2′C h2 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Leading dia. 3 feet 1 inch (0.940 m) Driver dia. 6 feet 7 inches (2.007 m) Length 66 feet 5 3⁄4 inches (20.26 m) Loco weight 80 long tons 19 cwt (181,300 lb or 82.2 t)  &emps; (Nos. 448–452 and 763–792)79 long tons 18 cwt (179,000 lb or 81.2 t)   (Nos. 453–457) 81 long tons 17 cwt (183,300 lb or 83.2 t)    (Nos. 793–806) Fuel type Coal Fuel capacity 5 long tons 0 cwt (11,200 lb or 5.1 t)  (Urie outside-frame bogie tender) Water cap 5,200 imp gal (23,600 l)   (Urie outside-frame bogie tender) 5,000 imp gal (22,700 l)    (Maunsell bogie tender) 4,500 imp gal (20,500 l)    (Drummond bogie tender) 4,300 imp gal (19,500 l)    (Drummond "watercart" tender) 3,500 imp gal (15,900 l)    (Six-wheel tender) Boiler pressure 180 psi (1.24 MPa)    (Urie batch) 200 psi (1.38 MPa)    (Eastleigh/Scotch batches) Cylinders Two, outside Cylinder size 22 in × 28 in (560 mm × 710 mm)    (Urie batch – as built) 21 in × 28 in (530 mm × 710 mm)    (Urie batch – as modified) 20 1⁄2 in × 28 in (520 mm × 710 mm)    (Eastleigh/Scotch batches)
Performance figures Tractive effort 26,245 lbf (116.74 kN)    (Urie batch unmodified) 23,900 lbf (106.31 kN)    (Urie batch as modified) 25,320 lbf (112.63 kN)    (Maunsell Batches)
Career Operators London & South Western Railway, Southern Railway, British Railways (Southern Region) Class LSWR: N15 SR / BR: King Arthur Power class LSWR / SR: A BR: 5P Locale Great Britain Withdrawn 1953–1962 Preserved SR No. 777 Disposition One preserved, remainder scrapped

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.

The new locomotives were built over several batches at Eastleigh and Glasgow, leading to the nicknames of "Eastleigh Arthurs" and "Scotch Arthurs" 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, 30777 Sir Lamiel, is preserved as part of the National Collection and can be seen on mainline railtours.