Joseph Armstrong designed a class of 2-2-2 standard-gauge passenger locomotives, ten of which were built in 1866 at the Swindon Works of the Great Western Railway (GWR). They were the first standard-gauge passenger tender locomotives to be built at Swindon. In 1869, a further 20 were built, also at Swindon, which differed little from the first 10, although the safety-valve covers were of different shape.
