In 1886 R and W Hawthorn was amalgamated with the shipbuilding company of Andrew Leslie, thus becoming R and W Hawthorn Leslie & Co. Ltd. In 1937 Robert Stephenson & Co. Ltd purchased the locomotive department of R & W Hawthorn Leslie & Co. Ltd. They became Robert Stephenson and Hawthorns Ltd.

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.