The class originally had very short saddle tanks. They were a Wolverhampton version of the Standard Goods class, which they resembled below the running plate. Between 1879 and 1895 the 16 in × 24 in (406 mm × 610 mm) cylinders were mostly enlarged to 17 in (432 mm), and the wheels enlarged to 4 ft 77⁄8 in (1.419 m) by means of thicker tyres. Most reboilering was done at Swindon rather than Wolverhampton, and with new boilers new, full-length tanks were fitted. From 1911 all but 11 of the class were rebuilt with pannier tanks, at the time that Belpaire fireboxes were fitted. After 1922 heavier boilers were used, and pressure increased. Many had new bunkers, of both Swindon and Wolverhampton design.
These engines were distributed between the Northern and Southern Divisions of the GWR. Apart from four scrapped before 1914 all ran well over a million miles; No. 1047, aged 65, was the last survivor, in summer 1935.