In 1937 Robert Stephenson & Co. Ltd purchased the locomotive department of R & W Hawthorn Leslie & Co. Ltd. They became Robert Stephenson and Hawthorns Ltd. The policy was to concentrate the building of main line locomotives at Robert Stephenson’s Darlington works and industrial locomotives at Forth Banks. In 1944 Vulcan Foundry acquired Robert Stephenson and Hawthorns Ltd, ending Hawthorns' 137 year connection with Forth Banks. In 1955 Vulcan Foundry became full members of the English Electric group of companies, which became part of the GEC group of companies in 1968.

The Vulcan Foundry was originally opened in 1830 at Newton-le-Willows, as Charles Tayleur and Company. It initially produced girders for bridges, switches and crossings, and other ironwork following the opening of the Liverpool and Manchester Railway. Robert Stephenson became a partner in 1832, and in the same year, the first locomotives ‘Tayleur’ and ‘Stephenson’ were delivered to the North Union Railway. By 1840 locomotives had been delivered to five European countries and to North America. The company became The Vulcan Foundry Company in 1847 and acquired limited liability in 1864. From the beginning of 1898, the name changed again to The Vulcan Foundry Limited, dropping the word 'company.' Vulcan locomotives were exported all over the world, with the first locomotives for Russia and Japan supplied in 1837 and 1871 respectively and a long association with India began in 1852. First World War production included shells, gun mountings and mine sweeping equipment. The first non-steam locomotive, an electric, was produced for India in 1929. The first diesel locomotive design commenced in 1932/33 and an agreement was reached with A/S Frichs in Denmark. The English Electric 6K engine was used from this time. The “Waltzing Matilda” tank was developed in 1938 and produced in large numbers and over five hundred ‘Austerity’ steam locomotives were produced for the War Department. Other wartime production included gun mountings and torpedo parts. In 1944 Vulcan acquired the locomotive business, Robert Stephenson & Hawthorns Ltd, based in Newcastle-upon-Tyne. In 1946 the company began working with the English Electric Company producing diesel and electric locomotives and became part of the English Electric Group in 1955. All locomotive building from Preston was transferred to Vulcan Foundry and Robert Stephenson’s in Darlington. Under the new ownership, the works produced many locomotives for both domestic and foreign railways, notably the Deltic. The mid-sixties saw the ‘RK’/’V’ engine production at Preston moved to Vulcan and Ruston & Hornsby Ltd merged with English Electric Diesels in 1966. After the General Electric Company plc (GEC) takeover in 1968 the Ruston name was used for some time inside what became GEC Diesels Ltd in 1975. Engine production and development continued for locomotive, industrial and marine applications until after the GEC-Alsthom merger in 1989. The company took over Mirlees Engines, Stockport in 1997 and was renamed Alstom Engines Ltd.