Dolgoch holds an important place in railway preservation history as it was the only serviceable locomotive on the Talyllyn Railway when it became the first ever preserved railway to be operated by volunteers in 1951, and largely single-handedly kept the railway going during this first season.
The design is unusual for a 0-4-0. The well tank engine has a long wheelbase and the driving axle is behind the firebox, which prevents the use of a conventional valve gear layout. Consequently, the Allan valve gear is driven from the leading coupled axle and doubled back to connect to the valve rods.
The engine was renamed "Pretoria" between about 1900 and 1914 in celebration of the relief of the township of Pretoria in South Africa by Lord Roberts during the Boer war. It then reverted to the original name "Dolgoch", which it retains to this day. In the top left photograph, the engine carries the name "Pretoria" - the freshly painted appearance hints that this photograph was taken after the repainting and name change (records indicate it was repainted and renamed around 1900, and would have been a bit paint-weary prior to that. When the image is darkened and zoomed in "Pretoria" can be read painted on the boiler side between the chimney and the side coal bunker). For most of the Railway's life, engine names were painted only on one side of the engines - the North side (the side facing the station platforms which were also only on this side for the whole line). Polished brass nameplates are a feature of current preservation.