This class of large prairie was created in 1938 when Collett rebuilt some of Churchward's 3150 Class engines for use as bankers, particularly from Severn Tunnel Junctionshed. These engines used the same standard class 4boiler, but with pressure increased to and smallerdriving wheels and a increase in cylinder diameter. This raised their tractive effort to. Less noticeable was a reduction in pony truck wheel diameter to. Only five engines were ever modified, Nos. 3173, 3156, 3181, 3155 and 3179 which were rebuilt as 3100 to 3104 respectively. All members of the class were scrapped.