This locomotive was built by Avonside Engine Company in 1914 as a class B3 0-6-0ST.
Between 1906 and 1926 59 locomotives were built to this design. Of these 26 operated on the Mersey Docks & Harbour Board Railway at Liverpool.
Sir John was employed in the coalfields where it was withdrawn from service in the early 1970s whilst based at Mountain Ash Colliery in South Wales.
It moved into preservation in May 1981.
The locomotive was stored by the Taff Vale Railway Society at British steel Dowlais Foundry until December 1987 when it moved to The Vale of Neath Railway Society at Abergarwed. Both proved to be failed preservation projects.
It has since been preserved on the Gwili Railway where it arrived in the summer of 1994.