Originally designed for the London & South Western Railway in 1920 by Robert Urie, the S15 was designed as a heavy freight locomotive to operate between London and the south coast ports. The class proved so useful that further batches were built by the Southern Railway in 1927 and 1936 with some modifications by their chief engineer Richard Maunsell.

S15s served on the Southern Railway and into British Railways days before retiring as part of the Modernisation Plan – the last journey a farewell tour in January 1966.

825 was built in April 1927 at Eastleigh works near Southampton and along with most of the class was allocated to Feltham. By the time of nationalisation she was based at Exeter Junction before moving to Salisbury in 1951 and remaining there until withdrawn in January 1964.

No. 825 is one of three S15 locomotives owned by the Essex Locomotive Society, all of which are stabled at the North Yorkshire Moors Railway. She was a regular on the line until her boiler ticket expired in 2013. The boiler is currently being overhauled in Scarborough while the tender and frames are worked on at Grosmont with a combination of ELS resources and NYMR help as required. It is hoped that 825 will return to steam during 2017.

The other two S15s – 830 and 841 “Greene King” are also stored at Grosmont, and both have acted as parts donors to keep 825 running. At present restoration of these two locomotives is a much longer-term project and there are insufficient resources available to make any plans for their restoration.