|Power Classification||4MT reclassified 5MT in 1953|
|Introduced||1931 – 1935|
|Driving Wheels||5ft 8ins|
|Boiler Pressure||225psi superheated|
|Cylinders||Outside – 18in x 30in|
|Valve Gear||Stephenson (piston valve)|
The large Prairie tanks were all developed from a prototype built in 1903. This was No 99. It was later renumbered 3100 and thirty-nine others were built in 1905-1906 and numbered 3111-31149. This was the old 3100 class. In 1906-1908 forty-one engines were built with larger boilers which formed the 3150 class.
|3100 class subsequently called 5100 class|
In 1929 the old 3100 class engines were renumbered in the 5100 series and they were known as the 5100 class. They had been superheated and were rebuilt by Collett with detail alterations and increased weight from 75t 10cwt to 78t 9cwt).
From 1929 onwards new locomotives were built to the modified design and these were known as the 5101 class. There were seventy locomotives in the 6100 class, built in two batches in 1931–1933 and 1935.
The 6100 class locomotives were another variation with increased boiler pressure to work on the London suburban area services where they replaced the ageing 2221 class.
|2221 class – County Tanks – Thirty were built between 1905 and 1912. All were withdrawn by the mid 1930s.|
End of Year
|Built||Withdrawals||No. in Service|
Typical duties were Paddington to Aylesbury via High Wycombe, and from the same terminus to Oxford, Windsor, Reading and Basingstoke. They were mainly shedded at Old Oak Common, Southall, Slough, Reading and Aylesbury throughout their lives. In1955, some were transferred to outlying branch lines and to banking duties through the Severn Tunnel. Withdrawals began in 1958, but the advent of the first generation of diesel multiple units in the early 1960s made them semi-redundant though generally far from worn out. Some remained in service until 1965 although the last few years saw them on more menial duties.