Editing GWR 2900 Class (section)

==Prototypes==
Between 1902 and 1905 Churchward built and tested three prototype locomotives with detail differences, before using the third as the basis for the production series.

===No. 100===
[[File:Prototype 4-6-0 No.100.jpg|thumb|left|No. 100 as built in 1902]]
The first prototype was completed at the [[Swindon Works]] of the GWR (Lot 132) in February 1902.<ref name=RCTS1>{{harvnb|le Fleming|1953 |p=H22}}</ref> It was numbered 100 and in June 1902 was named ''Dean'' (later ''William Dean'') to mark the latter's retirement. The new design incorporated all of Churchward's current ideas including a domeless [[fire-tube boiler|parallel boiler]], raised [[Belpaire firebox]], {{convert|19|in|cm|1|abbr=on}} diameter outside cylinders with {{convert|30|in|cm|1|abbr=on}} piston stroke, and boiler pressure of {{convert|200|psi|MPa|2|abbr=on|lk=on}}.<ref name=Nock12>{{harvnb |Nock |1983b |p=12}}</ref> The piston valves were driven by rocking levers actuated by the expansion link of [[Stephenson valve gear]] – this particular design was only used on No. 100.<ref name=Nock21>{{harvnb |Nock |1983b |p=21}}</ref> The parallel boiler was later replaced with a [[fire-tube boiler#taper boiler|taper boiler]], and then the first [[superheater|superheated]] taper boiler in 1910. 

Churchward had studied American boiler design, but he was also later influenced by [[Continental Europe|continental]] practice in efficient motion design. A [[Compound locomotive#De Glehn|de Glehn]] [[4-4-2 (locomotive)|4-4-2]] compound engine was ordered from the [[Société Alsacienne de Constructions Mécaniques]] (SACM) for comparative trials on the GWR.<ref name=GWS29xxOvw>[http://www.greatwestern.org.uk/m_in_snt.htm Great Western Society – GW 2900 Class overview] (Accessed 26 April 2009)</ref> According to E.C. Poultney, No. 100 was the first 4-6-0 locomotive to have high enough boiler capacity and steam ports large enough to handle the steam flow required by large cylinders: "The engine probably influenced to a large extent the use made of engines of the 4-6-0 type".<ref name=Poulteney1>{{harvnb|Poultney|1952 |p=47-7}}</ref> No.100 was renumbered 2900 in 1912, and was withdrawn from service in 1932.

===No. 98===
[[File:GWR 4-6-0 No.98.jpg|thumb|left|The second prototype No. 98 as built 1903]]
A second prototype locomotive, No. 98, was built at Swindon Works in March 1903 (Lot 138) to a similar design but with a taper boiler, re-designed valve gear layout and cylinders and a shorter wheelbase.<ref name=RCTS2>{{harvnb |le Fleming|1953 |p=H23}}</ref> Valve diameters were increased from {{convert|6+1/2|in|mm}} to {{convert|10|in|mm}}.<ref name=GWS29xxOvw /> According to Poultney, these improvements "may truly be said to be the keystone of the arch upon which all modern locomotives are designed".<ref name=Poulteney2>{{harvnb|Poultney|1952 |p=66}}</ref> In 1906 this locomotive was re-boilered with a {{convert|225|psi|MPa|2|abbr=on|lk=on}} boiler to correspond with the third prototype. This prototype locomotive was named ''Vanguard'' in 1907 (renamed ''Ernest Cunard'' in the same year). It was renumbered 2998 in 1912, received a [[superheater|superheated]] boiler in 1911 and was withdrawn in 1933.

===No. 171===
A third prototype, No. 171, was built at Swindon in December 1903 (Lot 145) incorporating the improvements to No. 98 but with a {{convert|225|psi|MPa|2|abbr=on|lk=on}}  boiler and minor amendments to the heating surface and grate area. It was built as a 4-6-0 but in October 1904 it was converted to a 4-4-2 to enable better comparison with the performance of the French built de Glehn 4-4-2 Compound; it was reconverted to 4-6-0 in July 1907.<ref name="RCTS2"/> The conversion was carried out by substituting {{convert|4|ft|1+1/2|in|m|3|abbr=on}} trailing wheels with outside suspension for the final set of driving wheels. It was named ''Albion'' in 1904, renumbered 2971 in 1912, received a [[superheater|superheated]] boiler in 1910 and was withdrawn in 1946. No. 171 formed the basis of the main production series, introduced in 1905, although at this time Churchward was still unsure of the relative merits of the 4-4-2 and 4-6-0 wheel arrangements.