Some feel that the 'Castle' Class locomotive was the ultimate in GWR locomotive development, rather than the 'Kings'. It was a development of Churchward’s 'Star' Class of 1907. Built at Swindon, they had longer frames, an increased cylinder size and a larger firebox. They were a post-Grouping design by Collett and were made over many years to produce one of the largest classes of locomotives on the GWR. The building programme did not finish until 1950 and so some of them went straight into BR livery. The class was built for express passenger duties which they fulfilled very well. 166 were built, the last one being withdrawn from service in 1965. Eight of them have been preserved.

There is little doubt that the Hornby Dublo model of Bristol Castle, of 1957, did much to popularise the subject amongst modellers. It is surprising, therefore, that it took until 1979 before a plastic bodied, 2-rail proprietary model was produced. This was the Airfix one which soon after passed to Palitoy (Mainline Railways) and thence to Dapol. It was Dapol who developed the Hawksworth tender and produced the Hawksworth 'County' variation of the model. In 1996 the 'Castle/County' tooling passed to Hornby and the first Hornby models arrived the following year.

Rovex Scale Models Ltd did not choose to model a 'Castle' in the early years but had chosen a 'Hall' instead. This was possibly because there was already the metal bodied 'Castle' in the rival Hornby Dublo rang, referred to above. They eventually had access to the tools to that model when Meccano Ltd joined the Lines (Tri-ang) Group in 1964, but passed them to their subsidiary, G&R Wrenn Ltd, along with much of the other Dublo tooling. Then, in 1996 they acquired the tools to the Airfix/Dapol 'Castle', as referred to above, and over the next 12 years made 28 versions of it. However, GWR enthusiasts kept reminding Hornby that the 'Castle' was being left behind by the rising standard of newly tooled models and that such a popular subject should itself be retooled. This Hornby eventually did and the new super-detailed model arrived in 2010.