The GWR 4100 Class was a class of steam locomotives in the Great Western Railway (GWR) of the United Kingdom.
The Badminton class express passenger 4-4-0 steam locomotives were introduced in 1897 as a development from the earlier Duke class. The name Badminton was chosen after the Duke of Beaufort's Badminton estate, through which the GWR was building a new line to South Wales at the time.
Further modifications to the design resulted in the Atbara Class entering service in 1900, the names for these locomotives generally being taken from contemporary military engagements or senior army commanders. Later engines were named after cities of the British Empire.
The final batch of locomotives were named after varieties of garden plant and in consequence were known as the Flower Class.
These three types were later standardised and treated as a single class, so are listed together here. Four other prototype 4-4-0s, originally built in 1894 as the Armstrong Class, were also later rebuilt as Badmintons (see below).
This class were subject to the 1912 renumbering of GWR 4-4-0 locomotives, which saw the Bulldog Class gathered together in the series 3300-3455, and other types renumbered out of that series. This class took numbers 4100-4172 (of which numbers 4101-4120 had previously been used by Flower Class locomotives).
The first member of the class, no. 3292, was completed in December 1897 with a domed parallel boiler, a raised Belpaire firebox and an extended, built-up smokebox similar to that used on the Duke Class. The outside frames were curved over each driving wheel axle. It was named Badminton in April 1898. A batch of eleven locomotives, nos. 3293 to 3303, were completed between April and July 1898, with a further batch of eight, nos. 3304 to 3311, between September 1898 and January 1899. The class were the first locomotives on the GWR to be fitted with copper Belpaire fireboxes. The penultimate example, no. 3310 Waterford, was fitted with a domeless parallel boiler, a steel Belpaire firebox, and an enlarged cab.