The GWR 2-6-2T was the mainstay of the Great Western Railway's suburban passenger services. Many classes were built and they were developed from one of George Jackson Churchward's pioneer designs – the experimental No 99. The basic design was so sound that derivatives were built until the end of the company's life in 1948 and even beyond. The development was gradual, but a little convoluted, and is summarised in this article.
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No. 99 was produced 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.
1906 saw the first alteration to the design of the class, when numbers 3150 to 3190 (known as the GWR 3150 Class) were produced using the larger standard number 4 boiler, again running at 200 psi. These two classes were the basis of what was to follow for over forty years.
A renumbering in 1927 saw the original 40 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.
1931 saw the next batch of engines, the initially 60-strong GWR 6100 Class. It had a useful alteration to the original design in the use of 225 psi (1.55 MPa) boiler pressure. This increased the tractive effort from 24,300 to 27,340 lbf (108 to 121.6 kN).
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.
The other modified class was from the 5100 series (ex 3100). This was rebuilt into the 8100 class and retained the number 2 boiler, but again pressed to 225 psi as in the 6100. Coupled wheels were of (yet another trifling reduced size) 5 feet 6 inches (1.676 m) in diameter. These too had the 3-foot pony truck wheels. These were intended to bolster the 6100 class on London suburban duties with a supposed benefit of better acceleration. Just how much difference the 2 inch variance actually made is open to question, given that wheels were designed to wear down by about that amount in normal service. Whatever the practical performance advantage, the class became widely dispersed and locos were used alongside their predecessors indiscriminately.
Just ten of these engines were rebuilt – numbers 5100 (the 1903 renumbered prototype number 99), 5123, 5118, 5145, 5124, 5126, 5120, 5116, 5133 and 5115, rebuilt as 8100 to 8109 respectively. In practical terms these were nothing more or less than the 6100 class with 2 inch smaller driving and pony truck wheels. In retrospect these rebuilds seem somewhat superfluous cases of fiddling with proven designs, given that later new builds reverted to the more or less original 1905 specification and dropped the non-standard driving wheel sizes and even the (probably more useful) higher boiler pressure.
The last 40 locomotives constructed were additions to the 4100 series in the final years of the GWR, and even into the second year 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.
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".
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