By 1918 it was apparent to the GWR Chief mechanical engineer George Jackson Churchward that his Star Class 4-6-0 locomotives would soon be incapable of handling the heaviest West of England expresses without assistance. He therefore proposed fitting the diameter boiler used on his 4700 Class 2-8-0 on to a 4-6-0 chassis, in 1919, to create a more powerful express locomotive, but was prevented from doing so by the weight restrictions on the GWR main line. The future problem was therefore left for his successor, C.B. Collett to solve.