First entering service in 1923, the 4 cylinder Castle Class was derived from the highly successful Star Class, with origins dating back to 1907. When introduced, the Castle Class was heralded as Britain's most powerful express passenger locomotive, being some 10% more powerful than the Star. So successful was the Castle Class that construction continued until 1950, by which time 171 had been built. From 1956, double chimneys and improved superheaters were installed to selected locomotives, resulting in "Drysllwyn Castle" achieving 160 kph (100 mph). The final Castle to run in British Rail service was "Clun Castle", which worked the last steam hauled train out of Paddington in 1965.
Aster's model, "Kingswear Castle" was finally withdrawn from service in April, 1963 and is available in either Great Western or British Rail livery.