The 5101 Class, or Large Prairies as they became know as, are a medium sized tank engine that was designed to operate stopping passenger services. Prairie refers to the 2-6-2 wheel arrangement that they were built with, and they were referred to as large for being bigger than the GWR 4500 and 4575 classes. Designed by Charles Collett, they were a development on George Churchward’s 3100 Class. They were built with the slightly larger No2 boiler and their coal bunker capacity was increased, and they had a lower axle loading than the 3100 Prairies. The 5101 class was then developed again after this with a higher boiler pressure, and the result was the 6100 class.
209 Large Prairies were built by both the GWR and British Rail. The history of Large Prairies is quite complex, but below is a quick summary of the class’ development.
The 209 included 50 3100s that were rebuilt from 1927 onwards. 50 5101s were ordered in 1927, with a further 50 being built including 40 by BR in 1948/49 under the 4100 numbering scheme.
40 3100s were introduced in 1903, including prototype No. 99 which became No. 3100, and was to be modified and renumbered 5100 in 1928, the rest of the class was modified and re-numbered 5111 to 5149. 40 3150s (tank engine version of the 4300 class) were introduced in 1906, with 50 5101s being introduced in 1929 following tests on no. 3100. This class was so successful that a further 60 were built, this time in the 4100 number scheme as all the 51—numbers had been used up, and then another 20 being built under BR with high superheat boilers in 1948/49. 70 6100s were also constructed between 1931 and 1935. 10 5100s were rebuilt as 8100s in 1938 and 5 3150s were rebuilt as bankers in 1938 and classified 31xx.
The GWR gave them the power classification of D with a Blue Route availability. They became the GWR main workhorses for the company, with their proven quality at the job they were built for. Under BR they were classified as 4MT.
Out of 209 Large Prairies built, eight of the 5101 class have survived into preservation, and one 6100:

  • 5164 (5164 Fund, based at the Severn Valley Railway)
  • 5199 (5199 Project Group, based at the Llangollen Railway)
  • 4110 (GWR Preservation Group at Southall, under restoration at Tyseley)
  • 4121 (Private Owner, based at Tyseley)
  • 4141 (Private Owner, currently at the Great Central Railway)
  • 4144 (Didcot Railway Centre)
  • 4150 (4150 Fund, based at the Severn Valley Railway)
  • 4160 (4160 Ltd, based at the West Somerset Railway)
  • 6106 (Didcot Railway Centre)

In addition 5193 was saved from Barry but has been converted by the West Somerset Railway as a mogul number 9351. 4115 survived as a member of the “Barry 10” but she is being broken up to assist with the construction of a new build 4700 class.