'Caerphilly Castle' locomotive in transit to the Science Museum, London, 1963.

The 'Castle' clas stream locomotives were designed by Charles Benjamin Collett (1871-1952) to provide the Great Western Railway with a more powerful locomotive than their existing 'Star' clas locomotives. 171 Castle clas locomotives were built between August 1923 and August 1950, the first of which was 'Caerphilly Castle', numbered 4073. Caerphilly Castle was displayed alongside Gresley's famous 'Flying Scotsman' at the 1924 British Empire Exhibition, Wembly, London.