'Dukedog' 9021 was one of sixteen of the class allocated to Machynlleth in the mid 'fifties, that depot having the majority of the remaining members of the class and also having responsibility for the large sub-shed at Aberystwyth. The Great Western needed a locomotive light enough to traverse the wooden Barmouth Bridge but capable of handling passenger and freight workings over the Cambrian system, and the solution was to use the frames from condemned 'Bulldogs' married with boilers and cabs from similarly condemned 'Dukes'.