Editing 4-2-2 (section)

===UK developments===
The [[London and North Western Railway]] No. 3020 [[LNWR 2-2-2 3020 Cornwall|Cornwall]] was built as 4-2-2 at [[Crewe Works]] in 1847, but was extensively rebuilt, and converted to a 2-2-2 in 1858.

[[Image:GWR broad gauge locomotives.jpg|thumb|[[GWR Iron Duke Class|Iron Duke]] class engines waiting to be scrapped]]
The one area where the type proved to be useful was on [[broad gauge]] locomotives, where sharp bends were less of an issue. [[Daniel Gooch]] built 29 examples of his [[GWR Iron Duke Class|Iron Duke]] express locomotive class for the [[Great Western Railway]] between 1847 and 1855.<ref>Bertram Baxter, British Locomotive Catalogue 1825-1923, Vol.1, Moorland Publishing, (1977), p. 55.</ref> They had an {{Convert|8|ft|abbr=on|adj=on}} diameter [[driving wheel]] size. Twenty examples of a similar [[Bristol and Exeter Railway 4-2-2 locomotives|design]] were built for the [[Bristol and Exeter Railway]] after 1849, by [[Avonside Engine Company|Stothert & Slaughter]] in [[Bristol]].<ref>Baxter (1977), p. 53.</ref> Because both sets of leading wheels are mounted independently in the frames in these classes, they are sometimes described as (2-2)-2-2 rather than 4-2-2.<ref>Science Museum, The British Railway Locomotive 1803-153, H.M.S.O., 1958, p.14.</ref>

The first 4-2-2 to have a bogie was built by [[Archibald Sturrock]] of the [[Great Northern Railway (England)|Great Northern Railway]] (GNR) in 1853. This had {{convert|7|ft|0|in|m|3|abbr=on}} [[flangeless driver|flangeless driving wheels]], and was only moderately successful, having a tendency to derail.<ref>{{cite book| last = Casserley | first = H.C. | title = Historic locomotive pocket book | place = London | publisher = Batsford | year = 1960 | pages = 15–16}}</ref> By the 1870s, improved design of bogies giving more flexibility enabled designers to create fast standard gauge express passenger locomotives of this type. On the GNR, [[Patrick Stirling (railway engineer)|Patrick Stirling]] built [[GNR Stirling 4-2-2|53 examples]] with [[Cylinder (locomotive)#Inside or outside cylinders|outside cylinders]] at [[Doncaster Works]] between 1870 and 1895, for use on the [[East Coast Main Line]] between [[London King's Cross railway station|London King's Cross]] and [[York railway station|York]]. They ran at an average speed of more than {{Convert|60|mph|abbr=on}} during the [[race to the north]], and were called ''eight-footers'' because of the [[driving wheel]], that was more than {{Convert|8|ft|abbr=on}} in diameter. Stirling's successor [[Henry Ivatt]] built a further twelve singles between 1898 and 1901 before moving on to larger [[4-4-2 (locomotive)|4-4-2]] designs.

The attraction of the 'single' (4-2-2 or otherwise) was that, thanks to the 'gearing' effect of the large single driving wheels, a locomotive could obtain high speeds while the operating speed of the engine's [[piston]]s and [[valve gear]] remained relatively low. This was important because of the relatively unsophisticated lubrication systems available at the time, with many of the parts of the engine's motion requiring to be 'oiled round' with the locomotive stationary before and after a run, or on longer trips by one of the crew taking to the [[running board]] to oil the required parts while on the move. Low piston speed also meant that the steam demand on the boiler would be relatively low, allowing a smaller, lighter boiler.

Before the development of the 'large boiler' designs in the 1890s, many boilers could not sustain the steam supply required of a small-wheeled locomotive operating at speed, thus requiring the large driving wheels of a single. At {{Convert|70|mph|abbr=on}}, an 'eight-footer' single's driving wheels would be revolving at 245 revolutions per minute, opposed to the 327 revolutions of the driving wheels of a 'six-footer'. A locomotive with coupled wheels also suffered extra rolling resistance from the presence of [[coupling rod]]s between the driving wheels which incurred a slight but measurable resistance arising from the small variances in the diameter of the driving wheels that were nominally of the same size. This meant that without the coupling rods, for a given locomotive speed the driving wheels would turn at very slightly different rate, but the coupling rods and the axles forced the driving wheels to turn at the same speed, with the added work being incurred as a binding force in the coupling rod bearings. Aside from this force, the coupling rod bearings themselves were a source of rolling resistance. Additionally, each driving axle of a locomotive had to be supported on large [[plain bearing]]s, with required further lubrication, introducing a potential point of mechanical failure through [[Hot box|overheating]] and a considerable source of friction. With only one driving axle, a 'single' had much less rolling resistance than a four-coupled engine, requiring less steam to achieve a given speed and also being more free-running when coasting downhill.

The 4-2-2 wheel arrangement had other specific advantages - the front [[bogie]] supported the weight of large cylinders and a long boiler which could exceed the load limits on a single front axle while also providing a superior stability and cornering at high speeds. Without restriction from a rear driving axle and wheels, a wide and deep [[Firebox (steam engine)|firebox]] could be used, carried by the small single trailing axle, which provided good steam-making properties and a large ashpan making these locomotives suitable for running long distances at high speeds.

The Stirling 'eight-footers' were very successful, but were best suited to the predominantly straight and flat GNR [[East Coast Main Line|main line]] in [[Cambridgeshire]] and the [[Vale of York]]. Other railways slowly replaced their original 'singles' with [[4-4-0]] locomotives that offered better traction at the cost of ultimate speed. However, in 1886 Francis Holt, manager at the [[Derby Works]] of the [[Midland Railway]] invented a practical form of [[Sandbox (locomotive)#Steam sanding|steam sanding gear]] which allowed locomotive crews to quickly and effectively stop wheelspin. This led to the Midland reviving the 'single' in the form of the distinctive [[Cylinder (locomotive)#Inside or outside cylinders|inside-cylinder]] "Spinners"; eighty-five were built to five designs by [[Samuel Waite Johnson]] between 1887 and 1900.<ref>Baxter (1977), p. 55.</ref> One [[Midland Railway 115 Class|115 class]], No. 673, survives at the [[National Railway Museum]] in York. Concurrent with Holt's invention was the so-called [[Race to the North]], when groups of railway companies on the [[East Coast Main Line|East Coast]] and [[West Coast Main Line|West Coast]] routes between London and Edinburgh competed with each for the fastest journey times. For its portion of the West Coast route, the [[Caledonian Railway]] used its unique 4-2-2, [[Caledonian Railway Single|No. 123]]. This had been built in 1885 as a showpiece for the 1886 [[International Exhibition of Industry, Science and Art|world's fair in Edinburgh]] rather than to fulfil a traffic need for the railway, and so had used the now-unfashionable 4-2-2 'Single' layout. But when pressed into service during the Race to the North, No. 123's high speed performance and reliability made other locomotive engineers reconsider the advantages of the single-driver engine, especially when joined with the new steam-sander (No. 123 had a similar sanding system working by compressed air).

These factors lead to a resurgence of interest in the 'single' for fast express passenger work in the 1880s and 1890s. [[William Dean (engineer)|William Dean]] of the Great Western Railway built fifty examples of the standard gauge [[GWR 3031 Class|3031]] ''Achilles'' Class from 1893 to 1899.<ref>Baxter (1977), p. 57.</ref> [[GWR 3031 Class#Notable members of the class|No. 3065 ''Duke of Connaught'']] contributed to the record-breaking run of the ''[[Ocean Mail]]'' express train from Plymouth to Paddington in 227 minutes on 9 May 1904, when it took over the train at Bristol from [[GWR 3700 Class 3440 City of Truro|No 3440 ''City of Truro'']] and completed the journey to Paddington in 99 minutes 46 seconds. By 1900, average train loads had grown beyond the capability of even a sander-fitted 'single' and their development was stopped. On the GNR, Stirling's famous 'eight-footers' required [[double heading]] with 4-4-0s before they were replaced by the [[GNR Class C1 (small boiler)|'Klondyke' 4-4-2]] engines designed by [[Henry Ivatt]], while on the Midland Railway Samuel Johnson developed a powerful compound 4-4-0 to replace his 'Spinners'.

Other notable [[UK]] examples of the 4-2-2 include the [[GER Class P43]], which was an early [[oil]]-burning engine, developed by the pioneer of [[oil]]-[[boilers]], [[James Holden (engineer)|James Holden]]. The last British 'single' to be designed was the Class 13 of the [[Great Central Railway]], designed by [[Harry Pollitt (engineer)|Harry Pollitt]] in 1900 for work on the company's new [[Great Central Main Line|main line]] to London. Ivatt Class A5 singles of the GNR, designed before the Great Central engines, continued to enter service during 1901, being the last of their type to take to the rails in Britain.