The GWR 2-6-2T was the mainstay of the Great Western Railway's suburban passenger services. Developed from one of George Jackson Churchward's pioneer designs – the experimental No 99 – a number of derivative classes were built over the period from 1906 to 1950. The development was gradual, but a little convoluted, and is summarised in this article.
No. 99 was built in 1903 and given an extended trial over the ensuing two years. Fitted with the standard number 2 boiler running at 200 psi (1.38 MPa), flat topped tanks and driving wheels of 5 feet 8 inches (1.727 m) in diameter, this was the genesis of 289 similar locos that were to follow. 39 more examples were built to this initial design. This production batch differed from the prototype only in that the tank tops were sloping to aid visibility and the cab sides were incorporated into the tanks. The running numbers of this batch were 3111 to 3149 and the prototype was logically renumbered 3100 and the class became the GWR 3100 Class.
In 1906 a further 41 locomotives were built with the larger standard number 4 boiler, again running at 200 psi. These were numbered 3150 to 3190 (known as the GWR 3150 Class). These two classes were the basis of what was to follow for over forty years.
5100 and 5101 classes
In 1927 the original 40 were renumbered 5100 and 5111 to 5149; the following additions to the class filled in the numbers 5101 to 5110 and extended the class to 5189. These locos were known as the GWR 5101 Class but were really little changed from the first batch, having an increased axle loading of 17 tons 12 cwt (39,400 lb or 17.9 t); the maximum permitted for the ‘Blue’ route availability. Bunkers were of the standard Collett design with greater coal capacity.
Additions to the 5100 class were made until available numbers were exhausted, and 40 engines were then built in the 4100 series.
In 1931 the initially 60-strong GWR 6100 Class were introduced, with an increased boiler pressure of 225 psi (1.55 MPa). This increased the tractive effort from 24,300 to 27,340 lbf (108 to 121.6 kN).
New 3100 class
In 1938 Collett rebuilt some of the oldest locos in the 3100 series with a view to using them as bankers, particularly from Severn Tunnel Junction shed. One of the two classes of rebuilds was a "new" 3100 class derived from the old 3150 class. These engines used the standard class 4 boiler again, but pressed to 225 psi and with smaller coupled wheels of 5 feet 3 inches (1.600 m) in diameter, and a half inch increase in cylinder diameter, nominal tractive effort rose to 31,170 lbf (138.7 kN). Almost impossible to notice was a 2 inch reduction in pony truck wheel diameter to 3 feet 0 inches (0.914 m). Only five engines were ever modified, namely 3173, 3156, 3181, 3155 and 3179 which were rebuilt as 3100 to 3104 respectively.
Ten members of the 5100 series were rebuilt with 5 feet 6 inches (1.676 m) driving wheels and 3-foot pony truck wheels. They retained the number 2 boiler, but again pressed to 225 psi as in the 6100. Numbers 5100 (the 1903 renumbered prototype number 99), 5123, 5118, 5145, 5124, 5126, 5120, 5116, 5133 and 5115, were renumbered 8100 to 8109. This 8100 class were intended to bolster the 6100 class on London suburban duties, with the smaller driving wheels giving a supposed benefit of better acceleration. Whatever the practical advantage in performance, the class became widely dispersed and locos were used alongside their predecessors indiscriminately.
The last 40 locomotives constructed were additions to the 4100 series, built during the final years of the GWR, and the first and second years of BR (WR) control.
Ten engines of the 4100/5100 series have been preserved. They are 5164, 5193, 5199, 4110, 4115, 4121, 4141, 4144, 4150 and 4160. The last three had very short careers in BR ownership, their time in preservation now easily representing the majority of their lives. 5164 - Severn Valley Railway, operational. 5193 - West Somerset Railway, operational. Converted to a 2-6-0 and now numbered 9153. 5199 - Llangollen Railway. Boiler ticket expired summer 2012. Currently being dismantled. 4110 - Tyseley. Formerly based at Southall. In ex-Barry condition. 4115 - Llangollen. Formerly part of the 'Barry 10'. Parts to be used in a converstion. 4121 - Tyseley. Missing pony trucks and in ex-Barry condition. 4141 - Epping and Ongar Railway. Operational. 4144 - Didcot Railway Centre. Undergoing overhaul. 4150 - Severn Valley Railway. Undergoing restoration. 4160 - West Somerset Railway. Opoerational.
The 2-6-2 wheel arrangement is nicknamed "Prairie", a name which originated in the USA. The name is completely inappropriate in Britain because there are no prairies but, nevertheless, it is often used. The locomotives described in this article are nicknamed "Large Prairies" while the smaller 4400, 4500 and 4575 classes are nicknamed "Small Prairies".