Editing 0-4-4-0 (section)

== Development ==
The first four-wheeled double-bogie locomotives were built by [[Horatio Allen]] in 1832. These were four double-boilered locomotives built by the [[West Point Foundry]] in [[New York (state)|New York]] for the
[[South Carolina Canal and Rail Road Company]], the first of these named ''South Carolina''. Although these had many of the features that would later become known as typical for Fairlies, the articulated bogies and the double boiler, the wheels of these bogies were not coupled and so they were instead of a {{whyte|2-2-0+0-2-2}} wheel arrangement. The 'double boiler' in this case also meant two narrow boiler barrels side by side at each end, four in total, not just double-ended.{{sfnp|Binns|2001|pages=2–4}}

The first 0-4-4-0 locomotive{{efn-lr|Although sometimes described as an 0-4+4-0.}} was the {{interlanguage link|Seraing (Semmering Trials locomotive){{!}}''Seraing''|de|SStB – Seraing}}, one of the contestants in the 1851 [[Semmering Trials]]. The [[Semmering railway]] was the world's first mountain railway and faced unprecedented gradients of 2.5%. This required the development of new techniques in locomotive design for which trials were held and the entrants used various forms of articulation in order to place the most useful power through their driving wheels. ''Seraing'' resembled what would become the double Fairlie design, with a double boiler and two articulated powered bogies beneath the frame.{{sfnp|Binns|2001|pages=2–4}}

After Semmering, some French engineers also experimented with duplex drive locomotives. [[Jules Petiet]], designed some unsuccessful classes of rigid duplexes with an {{whyte|0-2-6-2-0}} (UIC: A3A) single-boiler but double-ended [[Crampton locomotive|Crampton]] in 1862 and a class of twenty {{whyte|0-6-6-0|T}}s in 1863.<ref>{{Cite web
  |title=Petiet's French Experiments.
  |website=Unusual Locomotives
  |author=Douglas Self
  |url=http://www.douglas-self.com/MUSEUM/LOCOLOCO/petiet/frexp.htm
}}</ref> [[Thouvenot]] in 1863 produced an {{whyte|0-6+6-0|T}} design which was closer to the Fairlie type, with a double boiler and swivelling bogies.{{sfnp|Binns|2001|pages=2–4}}<ref>{{Cite journal
  |journal=[[Minutes of the Proceedings of the Institution of Civil Engineers|Min. Proc. Inst. of Civ. Engr.]]
  |title=Discussion on the Working of Steep Gradients and Sharp Curves on Railways
  |first=H W  |last=Tyler
  |collaboration=
  |volume=26  |issue=1867
  |year=1867
  |page=325
  |doi=10.1680/imotp.1867.23165
 |url=https://www.icevirtuallibrary.com/doi/pdf/10.1680/imotp.1867.23165
}}</ref>

=== Meyer locomotives ===
[[File:Monarch Llanfair Caereinion Welshpool & Llanfair '76 (31977941251).jpg|thumb|[[Monarch (locomotive)|''Monarch'']], a Bagnall-built Meyer of 1953]]
{{further|Meyer locomotive}}

The first Meyer locomotive, ''L'Avenir'', was built in 1861 and was also derived from a Semmering Trials design, the {{interlanguage link|Neustadt (locomotive){{!}}''Neustadt''|de|SStB – Neustadt}}. This had a similar arrangement of two power bogies to ''Seraing'', but a conventional single boiler. Meyer used compounding at first and so the cylinders were placed at the inner end of the bogies, where the intermediate pressure pipework between them could be kept shorter.

The most numerous Meyer locomotives were a German {{TrackGauge|750mm}} narrow gauge class, the [[Saxon IV K|DRG Class 99.51–60]], of which 96 were built.

The need to place the boiler above the bogies limited the depth of the [[firebox (steam locomotive)|firebox]]. [[W. G. Bagnall]] worked around this by using [[Bagnall boiler|their own boiler design]] with an internal firebox within the circular shell.

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=== Fairlie locomotives ===
[[File:Snake, a double Fairlie, B class steam locomotive B 238 (0-4-4-0T). ATLIB 257541 (cropped).jpg|thumb|An [[Avonside Engine Company|Avonside]]-built [[NZR B class (1874)|New Zealand Fairlie]] of 1874]]
{{further|Fairlie locomotive}}

A decade after ''Seraing'', [[Robert Fairlie]] revived the concept and was granted a patent for his design in 1864.<ref>{{Cite patent
  |country=GB
  |number=1210
  |title=
  |pubdate=12 May 1864
}}</ref><ref>{{Cite web
  |title=Fairlie's Patent
  |website=Festipedia
  |url=https://www.festipedia.org.uk/wiki/Fairlie%27s_Patent
}}</ref> It is not known how aware Fairlie was of the other European attempts.{{sfnp|Binns|2001|pages=2–4}} Placing the cylinders at the outer ends of the power bogies left a space between them and allowed depth for a conventional firebox, grate and ashpan.

The first [[Fairlie locomotive|Fairlie]] was an 0-4-4-0T built for the [[Neath and Brecon Railway]] in 1866, but the design came to prominence in 1869 with ''[[Festiniog Railway Little Wonder|Little Wonder]]'' for the [[Ffestiniog Railway]] in [[North Wales]] followed by five others. One locomotive was supplied to the [[Denver and Rio Grande Railroad]] in 1872. The type was also used in  [[Mexico]], [[New Zealand]] and [[Russia]] on [[Transcaucasian Railway]].

==== Survivors ====
There are five examples of surviving Fairlie 0-4-4-0T locomotives on the [[Ffestiniog Railway rolling stock|Ffestiniog Railway]]. Two of these are survivors from the original 19th century line; ''Merddin Emrys'' is still in service. Three were built new during the preservation era, the latest ''James Spooner'', was completed in 2023.

''Josephine'', a [[Vulcan Foundry]]-built [[Double Fairlie]], built in 1872 for the [[Port Chalmers Branch|Dunedin and Port Chalmers Railway Company]],{{sfnp|Joy|2012|pages=12–13}} survives as a static exhibit in [[Dunedin]], New Zealand.

=== Péchot-Bourdon locomotives ===
{{further|Péchot-Bourdon locomotive}}

These were a small Fairlie in all but name, with a few differences to allow a French patent to be granted in 1887.{{sfnp|Joy|2012|pages=18–21}} They were employed over short distances in French {{track gauge|600mm|lk=on|disp=1}} military railways.{{sfnp|Joy|2012|pages=18–21}}

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=== Mallet locomotives ===
[[File:Mallet 101 POC Noyelles.jpg|thumb|0-4-4-0T {{track gauge|metre gauge|lk=on|disp=1}} Mallet of the [[PO Corrèze]]]]
{{further|Mallet locomotive}}

The most numerous 0-4-4-0 locomotives were the [[Mallet locomotive|Mallet]] design. These are [[articulated locomotive|articulated]] [[compound locomotive]]s. The rear wheels and cylinders were fixed to the frames, as for a conventional locomotive. The front set formed a bogie that was pivoted at its rear and supported the front of the boiler on a sliding pad. As a compound, the lower pressure cylinders were always the swivelling bogie, as this only required the lower intermediate pressure to be passed through the pivoting steam pipe. The first of these was for a {{track gauge|600 mm|lk=on|disp=1}} [[Decauville]] light railway in 1887. Like the Fairlies, these were intended for narrow gauge lines built with tight curves.{{sfnp|Riemsdijk|1994|pages=42-44}} The most numerous 0-4-4-0T and 0-4-4-0[[tender-tank locomotive|TT]] Mallets were small locomotives of 600&nbsp;mm and {{track gauge|750 mm|lk=on|disp=1}} gauge built for the [[Java]]n sugar plantations in the 1900s and 1910s by companies like [[Orenstein & Koppel]] and the Dutch [[Du Croo & Brauns]],{{sfnp|Bruin|1987}} some of which were still operating into the 21st century.{{sfnp|Joy|2012|pages=50–51}}

[[File:4601D2x22SBBCFFFFSi.jpg|thumb|Swiss Central {{interlanguage link|SCB D 2×2/2{{!}}D 2×2/2|de|SCB D 2×2/2}} tender Mallet]]
Switzerland persisted with the 0-4-4-0T and 0-4-4-0 types and in the 1890s [[Maffei (company)|J.A. Maffei]] built classes of each for the [[standard gauge]] [[Swiss Central Railway]].{{sfnp|Riemsdijk|1994|page=44}}

The Mallet type developed and outgrew the original wheel arrangement, particularly in the US, also gaining tenders and often being simple expansion engines rather than compounds.{{sfnp|Riemsdijk|1994|pages=42-46}}

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