This article is about the 5 locomotives rebuilt in 1938/9 from the 3150 Class. For the 40 locomotives built in 1903–06 as the 3100 class, see GWR 5100 Class.
This class of large prairie was created in 1938 when Collett rebuilt some of Churchward's 3150 Class with a view to using them as bankers, particularly from Severn Tunnel Junction shed. These engines used the standard class 4 boiler again, but pressed to 225 psi (1,550 kPa). and using smaller coupled wheels of 5 feet 3 inches (1.600 m) diameter, and one-half inch (13 mm) increase in cylinder diameter, nominal tractive effort rose to 31,170 pounds (14,140 kg). Almost impossible to pick out was a 2 in (50.8 mm) reduction in pony truck wheel diameter to 3 ft 0 in (914 mm). Only five engines were ever modified, namely 3173, 3156, 3181, 3155 and 3179 which were rebuilt as 3100 to 3104 respectively. None of these were preserved.
Whitehurst, Brian (1973). Great Western Engines, Names, Numbers, Types and Classes (1940 to Preservation). Oxford, UK: Oxford Publishing Company. pp. 30, 102, 135. ISBN 978-0-9028-8821-0. OCLC815661.