Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement with no leading wheels, four powered and coupled driving wheels on two axles and two trailing wheels on one axle. While the first locomotives of this wheel arrangement were tender engines, the configuration was later often used for tank engines, which is noted by adding letter suffixes to the configuration, such as for a conventional side-tank locomotive, for a saddle-tank locomotive, for a well-tank locomotive and for a rack-equipped tank locomotive.
Overview
The earliest recorded locomotives were three goods engines built by Robert Stephenson and Company for the Stanhope and Tyne Railway in 1834.
thumb|left|[[LMR 57 Lion|LMR 57 Lion]]
The first locomotive built in Germany in 1838, the Saxonia, was also an . In the same year Todd, Kitson & Laird built two examples for the Liverpool and Manchester Railway, one of which, LMR 57 Lion, has been preserved. The Lion had a top speed of and could pull up to .
Over the next quarter of a century, the type was adopted by many early British railways for freight haulage since it afforded greater adhesion than the contemporary passenger configuration, although in time they were also used for mixed-traffic duties.
Usage
Austria
The Emperor Ferdinand Northern Railway (Kaiser Ferdinands-Nordbahn) acquired the locomotives Minotaurus and Ajax from the British manufacturer Jones, Turner and Evans in 1841, to work the line between Vienna and Stockerau. The locomotive Ajax has been preserved at the Vienna Technical Museum since 1992 and is described as the oldest preserved steam locomotive on the European continent.
Finland
In Finland, the 0-4-2 wheel arrangement was represented by the Classes B1 and B2.
The Finnish Steam Locomotive Class B1 is an 0-4-2ST locomotive, built from 1868 to 1890 by Beyer, Peacock and Company at Gorton Foundry in Manchester, England.
Hawaii
thumb|The Olomana
Although the type was not used by any major railroads in North America, HK Porter and the Baldwin Locomotive Works produced many small tank locomotives of this type for industrial and plantation work. The Olomana, built by Baldwin in 1883, arrived in the Kingdom of Hawaii in August 1883 after a two-month journey around Cape Horn. It was owned by Waimanalo Sugar Company on the island of Oahu and hauled cane from the fields to its refinery.
Indonesia
thumb|left|B25-02 Steam Locomotive at Ambarawa Railway Museum
In 1905, the Nederlandsch Indische Spoorweg Maatschappij (NIS) opened a line between Yogyakarta and Ambarawa via Magelang to facilitate the mobilization of Royal Dutch East Indies Army (KNIL) forces from Fort Willem I, line between Secang–Kedungjati passed a hilly region which requiring rack railway because of the 6.5% gradients. So, the NIS ordered 5 units of 0-4-2RTs wood burning NIS Class 230s that were came in 1902 and 1906 from Maschinenfabrik Esslingen, Germany. They were four-cylinder compound locomotives with two of the cylinders working the pinion wheels.
During Japanese occupation of the Dutch East Indies in 1942, all of Dutch East Indies railways locomotives had been renumbered, for all NIS Class 230s were changed to B25, from five of them only three left. There are two examples of B25 class locomotive still in operation, namely B25-02 and B25-03. Both were based in Ambarawa, where they have served for more than a hundred years. Locomotive B25-01 may also still be found as static display at the entrance to the Ambarawa Railway Museum.
On the island of Sumatra, there are some larger cousins of this class being used for hauling coal trains, namely the D18 and E10 classes.
New Zealand
thumb|[[NZR C class (1873)|NZR C class of 1873]]
The 0-4-2T arrangement was used by two classes of locomotives operated by the New Zealand Railways Department. The first was the C class of 1873, originally built as an 0-4-0T. The class was found to be unstable at speeds higher than , so by 1880 all members of the class had been converted to 0-4-2T to rectify this problem.
The second and more notable 0-4-2T class, and the only one actually built as 0-4-2T, was the unique H class designed to operate the Rimutaka Incline on the Wairarapa Line. The incline's steep gradient necessitated the use of the Fell mountain railway system, and the six members of the H class spent their entire lives operating trains on the Incline. Except for a few brief experiments with other classes, the H class had exclusive use of the Incline from their introduction in 1875 until the Incline's closure in 1955. Class leader, H 199, is preserved on static display at the Fell Engine Museum in Featherston and is the only extant Fell locomotive in the world.
The 0-4-2T arrangement was also employed for steam locomotives operated by small private industrial railways and bush and mineral tramways. One such locomotive, built by Peckett and Sons in 1957, is currently operational on the Heritage Park Railway, Whangarei. It is one of four such locomotives imported from Peckett, and was the last steam locomotive imported into New Zealand before dieselization.
Two others worked alongside her and are preserved, whilst the fourth was owned by a forestry railway, who converted it to a diesel locomotive.
South Africa
Standard gauge
thumb|[[Cape Town Railway & Dock 0-4-0T|Blackie plinthed at Cape Town railway station]]
In September 1859, Messrs. E. & J. Pickering, contractors to the Cape Town Railway & Dock Company for the construction of the Cape Town-Wellington Railway, imported a small steam locomotive from England for use during the construction of the railway. This was the first locomotive in South Africa. In , the locomotive was rebuilt to a configuration before it was shipped to Port Alfred, where it served as construction locomotive on the banks of the Kowie river and was nicknamed Blackie. It has been declared a heritage object and was plinthed in the main concourse of Cape Town station.
In 1860, the Cape Town Railway & Dock Company took delivery of eight standard gauge tender locomotives with an wheel arrangement for service on the Cape Town-Wellington Railway, which was still under construction. They remained in service on this line while it was being converted to dual standard-and-Cape gauges from around 1872 and were only retired in 1881, when sufficient Cape gauge locomotives were in service.
- The later class of four 32 Tonner rack locomotives, built by Esslingen in 1894 and 1897, was equipped with pinions for use on the rack railway section between Waterval Onder and Waterval Boven in the eastern Transvaal. They survived through the Imperial Military Railways (IMR) and CSAR eras and, even though the rack section was removed in 1908, they were still in service in 1912 when they were taken onto the SAR roster as obsolete unclassified locomotives.
thumb|[[Namaqualand 0-4-2ST Pioneer|Pioneer derailed outside O'okiep after a Boer commando attack]]
The Namaqua Copper Company's first gauge locomotive, acquired in 1901, was a Dick, Kerr & Co. built named Pioneer which was rebuilt from the configuration, possibly due to the additional weight of fuel tanks which were installed under the cab when it was converted to use fuel oil. The company also operated four more locomotives, one 9 Ton and three 12 Ton, possibly also acquired from Dick, Kerr & Company.
In 1904, a single gauge locomotive named Caledonia was placed in service by the Cape Copper Company as a shunting engine at O'okiep in the Cape Colony.