No. 100

The first prototype was completed at the Swindon Works of the GWR (Lot 132) in February 1902.^[2] 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 parallel boiler, raised Belpaire firebox, 19 in (48.3 cm) diameter outside cylinders with 30 in (76.2 cm) piston stroke, and boiler pressure of 200 psi (1.38 MPa).^[3] 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.^[4] The parallel boiler was later replaced with a taper boiler, and then the first superheated taper boiler in 1910. Churchward had studied American boiler design, but he was also later influenced by continental practice in efficient motion design. From the Société Alsacienne de Constructions Mécaniques (SACM) a de Glehn 4-4-2 compound engine was ordered for comparative trials on the GWR.^[5] 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to a large extent the use made of engines of the 4-6-0 type".^[6] No.100 was renumbered 2900 in 1912, and was withdrawn from service in 1932.

No. 98

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.^[7] Valve diameters were increased from 6+1⁄2 inches (170 mm) to 10 inches (250 mm).^[5] According to Poultney, these improvements "may truly be said to be the keystone of the arch upon which all modern locomotives are designed".^[8] In 1906 this locomotive was re-boilered with a 225 psi (1.55 MPa) 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 It was renumbered 2998 in 1912, received a superheated boiler in 1911 and was withdrawn in 1933.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 225 psi (1.55 MPa) 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.^[7] The conversion was carried out by substituting 4 ft 1+1⁄2 in (1.257 m) trailing wheels with outside suspension for the final set of driving wheels. It was named Albion in 1904, renumbered 2971 in 1912, received a 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.

Scott series

Whilst 171 was undergoing trials in 1905 nine further locomotives were ordered to be built at Swindon Works to a similar design (Lot 154) followed by a further ten (Lot 158), totalling 19 locomotives in this series. Thirteen of these were built as 4-4-2s and six as 4-6-0s. However, by January 1913, Churchward was persuaded by the superior adhesion provided by a 4-6-0 and they had all been converted to this wheel arrangement.^[9] The new locomotives were numbered 172–190 (renumbered 2972–2990 in 1912). Twelve of the series were named after characters in the novels of Sir Walter Scott. Directors of the GWR accounted for most of the other names. The series was withdrawn between 1931 and 1951.

Ladies

A second series of ten similar locomotives appeared in May 1906 (Swindon Lot 164), numbered 2901–10 and named after historical, mythological or poetical 'Ladies'. Nos. 2904–6 had short tapered boilers and short smokeboxes, whereas Nos. 2902–03 and 2907–10 had longer versions. All except 2901 had 18.125 in × 30 in (460 mm × 762 mm) cylinders, giving a tractive effort of 23,382 lbf (104.01 kN). No. 2901 Lady Superior was the first British locomotive to be built with a modern Schmidt superheater.^[7] The remainder of the locomotives were fitted with Swindon No.3 superheaters between 1909 and 1911 and were withdrawn between 1933 and 1952.

In May 1906 Charles Collett, then assistant manager of Swindon Works, supervised a demonstration run of number 2903 Lady of Lyons, newly released from the erecting shop. By mile-post timings observed from the engine and from passing times recorded at Little Somerford and Hullavington signal boxes, 4+1⁄2 miles apart and with a descending gradient of 1 in 300 between them, a speed of approximately 120 miles per hour (190 km/h) was recorded, but not in a sufficiently accurate manner as to be considered a record.^[10][11][12]

Saints

A third series of twenty further locomotives appeared during August and September 1907 (Swindon Lot 170), numbered 2911–30 and named after Saints. The framing for these had long curved ends under the cab and over the cylinders, which greatly improved the rather angular appearance of the earlier locomotives. They were fitted with cone boilers and smokeboxes. In October 1908, No. 2922 Saint Gabriel was fitted with a Swindon No. 2 superheater. The following year the Swindon No. 3 superheater became standard for the class.^[13] Between 1909 and 1912 the remainder of the locomotives were fitted with the Swindon No. 3 superheater. The Saints were withdrawn between 1932 and 1951. No. 2925 Saint Martin was rebuilt with smaller wheels in December 1924 to become the prototype Collett 4900 and renumbered 4900 but still carrying the same name.

Courts

A fourth series of 25 locomotives appeared during the years 1911 to 1913 (Swindon Lots 185, 189 and 192). These were numbered 2931–55 and named after famous Courts (i.e. mansions). They were all built with superheaters and there were detailed differences between the boilers used on different lots.^[13] They were all withdrawn between 1948 and 1953.