For power class 3, first a tank locomotive with a 2-6-2 wheel arrangement was developed. Its running gear was based on that of the Ivatt class 4 tender locomotive of the LMS, and other parts also came from this. However, the boiler was based on the GWR's standard No. 2 boiler used on the class “Large Prairie” 5101 and the class 5600. Shortly after the last locomotives were put into service, diesel multiple units were delivered, which contested part of their service area. Nevertheless, the first withdrawals did not take place until 1964 and the last ones were completed in 1967. 