 9000 was built in 1945, but the remaining 99 were built under British Railways jurisdiction in the period 1948–1950.The class, at least on paper, should have been very free steaming and powerful engines but, in practice, they were not suited to the work to which they were assigned.The engines had driving wheels, which would give them excellent power at low speed, such as that required for freight work, but these engines were intended for passenger use.