The Great Western Railway’s large Class 42xx, 52xx and 72xx tank engines were an evolution of a design first conceived in 1906 by George Jackson Churchward, Chief Mechanical Engineer of the Great Western Railway between 1902 and 1922.The 2-8-0 Class 42xx was the first of its type to be used in Britain and arose because of a need for a powerful freight locomotive capable of handling increasing heavy mineral loads, especially in South Wales.
Sharing a number of parts with the Class 28xx tender locomotives, some degree of side play in the rear two pairs of driving wheels, as well as thinner flanges on the middle two pairs, enabled the engines to negotiate tighter curves, right down to two chains in radius.The first production batch proved a huge success and 105 locomotives were built between 1910 and 1923. With rising costs and falling revenue during the 1920s, the new CME of the GWR, Charles Collett, decided it was more practical and economic to modify existing locomotive designs, rather than create new, untried ones. The class underwent extensive detail alterations and modifications, including having the cylinders increased in size and the addition of outside steam pipes, resulting in an increased tractive effort and a new classification of Class 52xx.
Production continued normally through to 1926, with 70 locomotives entering traffic, but the effects of the Great Depression of the 1930s had a marked impact on the finances and running of the GWR. The twenty 52xx locomotives built under Lot 266 in 1930 were sent straight into storage, but Collett decided to make use of these engines by altering them to 2-8-2T locomotives. Adding 4 feet to the frame and a trailing radial axle and wheels, these changes increased their coal carrying capacity, creating the Class 72xx, the first 2-8-2T locomotive to be built in Britain and the largest tank engine to run on the GWR.One of the final batch of 42xx locomotives built to Lot 220 at Swindon in August 1921, 4287 spent its British Rail life allocated to 86H Aberbeeg Shed in South Wales, from where it was withdrawn to Swindon for disposal in 1961, being cut up in April that year.