GWR 4100 Atbara/Badminton Class

The GWR Atbara and Badminton Classes were two related series of inside-cylinder 4-4-0 express passenger locomotives designed by William Dean and built at Swindon Works in 1898–1901, representing the peak of Dean's inside-cylinder 4-4-0 express design before Churchward began introducing his outside-cylinder types from 1902. Both classes used 6 ft 8½ in coupled wheels and similar boiler specifications, differing primarily in their firebox proportions and detail dimensions.

The Badminton Class (1897–1899, named after country houses including Badminton itself) was Dean's first really successful inside-cylinder 4-4-0 express, giving the GWR a type capable of genuine express running on the main lines to Bristol, Birmingham, and the West of England. The Atbara Class (1900–1901, named after military victories including the Battle of Atbara of 1898) was a development of the Badminton with minor boiler improvements, and Churchward applied his long-travel valve gear modifications to both classes as he took over the GWR's locomotive programme, significantly improving their performance.

Both classes had a complex later history as Churchward rebuilt many examples with his standard No. 4 boiler, creating what became known as the City Class when fitted with larger boilers — of which City of Truro, the celebrated locomotive that allegedly reached 100 mph in 1904, is the most famous. Several survivors of the Atbara and Badminton rebuilds effectively became City Class locomotives in all but name. None of the original Atbara or Badminton configuration was preserved, but City of Truro (rebuilt from an Atbara) is preserved at the Steam Museum, Swindon.