Douglas is a narrow gauge steam locomotive. It was built by Andrew Barclay Sons & Co. Ltd. in 1918. It was originally used by the Air Service Constructional Corps (RAF) then was bought in 1949 by Abelson & Co. (Engineers) Ltd. who then sold it to the Talyllyn Railway in 1953.
Douglas spent most of its working life at RAF Calshot near Southampton, and was later bought by an engineering company called Abelson's. In the early days of preservation, the Talyllyn Railway had contacted this and other similar firms, asking for redundant equipment. Abelson's offered the locomotive to the Talyllyn, and in return they named it after the donor, Douglas Abelson. After presentation in 1953 the locomotive was retubed and converted from 2ft gauge at Griffin Foundry, Oldbury before being taken by road to Towyn.
Although smaller than the other locomotives on the Talyllyn Railway, it has performed well and was returned to service in 1995, with a new boiler fitted, and turned out in its old Air Ministry Works & Buildings livery.
In recent years Douglas has been painted in standard Talyllyn Railway livery of deep bronze green lined with black borders and yellow lining; however as of 2010 it is painted red, acting as Duncan from the fictional Skarloey Railway. Upon its return in 2013, it will still be in a red livery, but will mainly run as Douglas and running as Duncan during school holidays.
All the steam-operated engines on the Talyllyn Railway (and diesel locomotive Midlander) appeared many times in The Railway Series books by the Rev. W. Awdry on the Skarloey Railway. Talyllyn's and Dolgoch's counterparts were Skarloey and Rheneas, respectively. Sir Haydn and Edward Thomas are represented in the series by Sir Handel and Peter Sam, whose original names were Falcon and Stuart. Douglas formed the basis for the character Duncan.