SECR K and SR K1 classes

Three factors dictated the type of locomotive that could operate on the South Eastern and Chatham Railway (SECR): the heavy passenger train loadings; the poor track quality; and the weak, lightly built bridges. This resulted in frequent double-heading, adding to operational costs. Richard Maunsell was appointed CME of the SECR in 1913, following the enforced retirement of Harry Wainwright, who had left a range of competent but unspectacular locomotive classes that struggled to cope with the increased train lengths and loadings. Maunsell reviewed the situation and planned to introduce six standard classes – using only two boiler designs – which would work the entire traffic of the railway. The first of these was the N class 2-6-0, which gave the SECR a capable mixed-traffic locomotive. For the express passenger design that could cope with the heavy boat trains, Maunsell wanted to enlarge the existing L class 4-4-0 with Walschaerts valve gear and an enlarged superheater, but this design would have resulted in a too heavy axle loading. Maunsell's newly recruited assistants, G.H. Pearson and Harold Holcroft from the Great Western Railway at Swindon and James Clayton from the Midland Railway at Derby, had recently been involved in the design of large passenger tank engines and persuaded him to use the 2-6-4 wheel arrangement, which would allow the class to operate at high speeds on the poor-quality track in north Kent. ==Design and construction==

The 2-6-4 wheel arrangement was not in common use in Great Britain at this time, as many railway companies operated routes that required locomotives with greater fuel capacity, or short branch lines that necessitated smaller locomotives. The 2-6-4 tank engine design had only been used once before for standard gauge locomotives in Britain, on the Great Central Railway's 1B class freight locomotives of 1914. However, the configuration was ideal for the SECR, because of its shorter mainlines, and allowed for a long wheelbase with a leading axle to permit greater stability at speed on track curves. The tightness of the curves on the former LCDR mainlines had constrained the size of locomotives operating on the SECR, as they had been hastily erected during the nineteenth century to compete with those of the South Eastern Railway (SER). The cab was fully enclosed, although the set of four small front spectacle plates (the windows on the front face of the cab for forward visibility) were the same as those used on the N class. The inclusion of these features is attributed to Holcroft, Maunsell's personal assistant, who had worked on the GWR 4300 class and the N class. James Clayton, Maunsell's Chief Locomotive Draughtsman, brought simpler and more functional Midland Railway influences to the design, such as the shape of the cab and the drumhead-type smokebox, which sat on a saddle that was of wider diameter than the fully lagged and clad boiler. The latter was fitted with Ross pop safety valves and pressed to . The firebox was narrower towards the rear and featured a continuously sloping grate, whilst the ashpan was fitted with front and rear damper doors, the latter adjusted to clear the rear driving axle. K class In January 1915 Maunsell received authority to build six examples, but, as with the N class, production was delayed due to the use of the Ashford works for wartime armaments manufacture. Assembly began in 1917 and the first, No. 790, emerged in July of that year. preceding the earlier N class design into service by one month. Further construction was deferred until after Ashford had caught up with the maintenance backlog caused by the war. Ten more locomotives were ordered by the SECR from Ashford works in June 1920, and to speed delivery the construction of frames, cylinders and side tanks was subcontracted to the Royal Arsenal at Woolwich. However, further severe delays at Ashford caused by the backlog of repair work meant that the boilers had to be supplied by the North British Locomotive Company. Construction of these locomotives had not begun by 1 January 1923, when the Railways Act 1921 merged the SECR with other railways in southern England to form the Southern Railway. As the locomotive proved suitable for the operating conditions of this section, the Southern Railway's Locomotive Committee proceeded with the assembly of the K class parts using outside contractors. Nine sets of parts (Nos. A791–A799) were conveyed to Armstrong Whitworth for assembly and the finished locomotives delivered in May and June 1925. These were allocated the numbers A610–A629, and work had begun on building the frames and cylinders when the order was cancelled following an accident at Sevenoaks in 1927 involving locomotive No. A800. They were to use the same boiler as the K and N classes and the general layout was similar to designs used by the GWR in South Wales. This arrangement was supplemented by two smaller-diameter outside cylinders with bore (compared to the cylinders of the K class), and a greater chimney diameter. It also featured a new cab design with redesigned single front spectacle plates, and a pair of substantially constructed steps were fitted behind both outside cylinders to provide access to the running plate. Only one locomotive of the K1 class was built; plans to build a further ten (Nos. A891-A900) alongside a batch of five N1 class 2-6-0s were cancelled after the Sevenoaks accident in August 1927. Following rebuilding as a 2-6-0 tender locomotive in 1928, No. A890 was reclassified U1 and was the forerunner of twenty more basically similar locomotives built in 1931. The first-completed Southern Railway K class No. A791 was named River Adur whilst the former SECR prototype was given the name River Avon; names were also allocated to the cancelled 1926 batch of locomotives. The K1 class locomotive No. A890 was named River Frome. The names were displayed on a rectangular brass nameplate fitted to the water tank sides. ==Operational details==

The K class was intended to haul the SECR's Kent expresses, and was trialled between Charing Cross, , and . No. 790 was also tested on fast Cannon Street, and Tonbridge trains during the spring of 1922, although rough riding between the latter two stations meant slower speeds over that part of route on subsequent runs. The Southern Railway's motive power re-organisation following the Grouping of 1923 expanded the class for operations over the Central section. These were modified in later batches, with limited success. The rough-riding was also attributed to the frames, which were of insubstantial construction to save weight. It was also found to have a wider route availability due to the smaller outside cylinders. The first derailment occurred at , near Maidstone on 31 March, when the flanges of the lead coupled wheel mounted the rails at . Although the official reports of these accidents blamed the poor quality of the track, a group of directors sought to have both classes banned from use on passenger services, but were overruled by the Southern Railway's Chairman of the Board of Directors, Everard Baring on grounds of cost. Accidents and incidents • In March 1927, locomotive No. 890 River Frome was hauling a train which derailed at Wrotham, Kent. • On 2 August 1927, Locomotive No. 800 River Cray was derailed at Maidstone, Kent. • On 20 August 1927, locomotive No. 890 River Frome was hauling a passenger train which was derailed at Bearsted, Kent. The cause was attributed to track defects. The locomotive was repaired and re-entered service on 23 August. It was involved in a serious accident the next day. Sevenoaks disaster The K and K1 classes suffered from stability problems when travelling at speed over points and curves. The locomotive was hauling a Cannon Street to express with a Pullman carriage when the leading driving wheels derailed at over catch points in a cutting. to gain an unbiased review of their riding qualities. When these engines returned from the LNER, the Southern Railway's General Manager, Sir Herbert Walker ordered further trials to be led by Sir John Aspinall on the Western section main line near . The 1928 accident inquiry did not attach blame to the Southern Railway for track maintenance or locomotive performance issues, and noted that the prototype had run for eight years over the same stretch of line without complaint. However, it identified the Brighton batch and No. A890 as being more susceptible to rolling on sharp curves with weak rail joints, although the entire class operated without incident on the former LBSCR network. The management of the Southern Railway realised that to have any success in operating the K class tanks on other parts of the network, vast stretches of track would require upgrading. ==Rebuilding==

. This is one of the rebuilds in British Railways service, No. 31803 at Bournemouth. As K class locomotive No. A803, it was named River Itchen. The rebuilding of the class as tender locomotives was cheaper than relaying track, particularly as in most respects the class had performed well. Rebuilding took place at Ashford, Brighton and Eastleigh railway works between March and December 1928, where the water tanks, rear bogie and coal bunker were removed. The straight-sided variant of Maunsell tender was attached, allowing a greater operational range for the locomotives. The Holcroft valve gear was later replaced with a third set of Walschaerts valve gear in February 1932, thus reducing maintenance. None of the rebuilds retained their names. The smaller-wheeled N class was preferred amongst crews for the same duties, as high-speed running was rare away from the main lines in the West Country. Heavier passenger work was allocated to Bulleid's Unrebuilt Light Pacifics, which were within weight restrictions in this area. Withdrawals took place between 1962 and 1966, by which time many of the rebuilds were based at Guildford shed. ==Livery and numbering==

SECR and Southern Railway The K class prototype was painted in an unlined dark grey livery with white lettering and numbering. This Maunsell grey livery was introduced by the SECR as a wartime economy measure. From 1925, the K and K1 classes were repainted in a darker olive green livery, introduced by Maunsell, with plain white lining and primrose yellow markings. This was carried into the Second World War when labour shortages meant that many U class locomotives were painted in plain black, with the result that by 1945 all the class were running in black. Rebuilds in British Railways service The K and K1 classes were absorbed by British Railways as part of the U and U1 classes in 1948, which were given the BR power classification 4MT (mixed-traffic) in 1950. The locomotives at first retained their Southern Railway livery, with "British Railways" added to the tender when repaints were due. Numbers were changed to the British Railways standard numbering system: the series 31790–31809 was allocated to the K class rebuilds, and 31890 to the K1 class. ==Operational assessment and preservation==

. Sir Nigel Gresley's independent report on the K and K1 classes during the mainline stability trials stated that they were well designed, mechanically reliable and capable of hauling expresses at high speeds on well-maintained track, which meant that they could have been useful additions to the Southern Railway's suburban commuter fleet. However, they were undoubtedly prone to rough riding and instability, and not only on the poorest quality tracks. It was restored to ex-British Railways condition as No. 31806. In August 2014, the locomotive entered service with the Swanage Railway. == See also ==