After the GWR had taken over the Cambrian Railways, they needed modern locomotives for passenger services on these lines which only allowed a low axle load. Since there were none of these locomotives available, they decided to mount the superheated boiler of Duke class No. 3265 “Tre Pol and Pen” to the intact frames of Bulldog class No. 3365 “Charles Grey Mott” in 1929. This prototype retained the number and name of the Duke.

Because this prototype was successful, 29 further locomotives were built in the same way between 1936 and 1939. They got numbers from 3200 onwards and were officially called “Earl” class. Due to their origin being a mix of the Duke and Bulldog classes, they were also called “Dukedog”. The only one that has been preserved is No. 9017 “Earl of Berkeley”, which hasn't been operational since 2011.