Six tank engines, to the same design, were built in 1926 by the Avonside Engine Co in Bristol. Numbered 1101 to 1106 they were specified and purchased by the Great Western Railway for use in the docks at Swansea. They were built to a standard Avonside design albeit with certain GWR mods including a Belpair firebox. The design incorporated outside cylinders and Walscherts valve gear. Features which were most un-GWR but allowed for easy maintenance and repair. In fact these six engines were unique in that they never visited the Swindon Works but had all repairs done locally. Apart from a brief period when two engines went to Port Talbot, they spent their entire life working around Swansea Docks. With the advent of the diesels they were withdrawn from service in 1959, each with mileages in excess of half a million.