Great Western Railway class 4200

When the 0-6-2T tank locomotives became too weak on the winding coal lines in South Wales, Churchward constructed a successor. Initially, he planned to develop a tank locomotive from his class 2800 2-8-0 by adding a trailing axle. After concerns about the ability to negotiate the tight curves, he omitted the trailing axle. He installed a smaller standard No. 4 boiler and reinforced the frames to carry the boiler and the supplies. The wheel flanges of the second and third driving axles were made thinner and the fourth driving axle had lateral play. 105 locomotives were built between 1910 and 1923 at Swindon.

In tests, the locomotives were said to be able to negotiate curves with a radius of 130 feet without derailing. When hauling coal trains of more than 1,000 tons, the small water supplies of only 1,800 gallons often became a problem. The successor class 5205 was created in 1923 by Collett by increasing the cylinder diameter from 18.5 to 19 inches. After 40 of the class 5205 had been rebuilt to the 2-8-2T class 7200 to increase their supplies, also 14 of the class 4200 were rebuilt to class 7200 between 1937 and 1939. They were withdrawn between 1959 and 1965. Five were preserved with two in working order, one under restoration and another one awaiting its overhaul as of early 2026.