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.

GEC Traction (GECT) was formed in 1972 as part of the GEC Power Engineering Group following earlier amalgamations of the traction divisions of the General Electric Company (GEC), the English Electric Company (EE) and Associated Electrical Industries (AEI). A wholly owned subsidiary company of GEC, the company had offices and works, located at Trafford Park in Manchester, at Strand Road in Preston, and at Attercliffe Common, Sheffield. The headquarters of GEC Traction was Trafford Park, Manchester (previously the headquarters of English Electric-AEI Traction) with design of rotating machines at Preston and Sheffield, and manufacturing activities for control equipment at Manchester and Preston. GEC Traction designed and manufactured a full range of traction machines and control equipment for electric vehicles, including electric locomotives and multiple unit trains for main-line and mass-transit railway systems (dc up to 3,000 volts, and ac up to 50,000 volts), diesel-electric locomotives and trains, mining and industrial locomotives, tramcars and trolleybuses. GEC Traction was the leading supplier of traction equipment in the UK and had a wide market around the world, particularly in South Africa, Australasia, Hong Kong, South Korea, South America and Pakistan. In 1979 the Industrial Locomotive Division of the former English Electric which was based at Vulcan Works, Newton-le-Willows was merged into GEC Traction, which later became a separate company, GEC Industrial Locomotives Ltd. During the late 1980s and 1990s the firm underwent major rationalisation, involving closure of several sites including Attercliffe Common in Sheffield in 1985 and the company’s headquarters at Trafford Park in Manchester in 1998. The company name GEC Traction endured until a merger with the French Alsthom group in 1989, which created GEC Alsthom Traction, which was still a branch of the main company GEC Alsthom.

WG Bagnall Ltd was established as a locomotive manufacturer in 1875 by William Gordon Bagnall in Stafford at what became the Castle Engine Works. Bagnalls first locomotive was produced in 1876, the company going on to produce machines for collieries and overseas plantations. The majority of the products that were manufactured were small four and six-coupled steam locomotives for industrial use, the company were noted for building steam and diesel locomotives in standard and narrow gauges. In 1891 Ernest Edwin Baguley joined the company, he left in 1902 to start his own business. Bagnalls introduced several novel type of locomotive valve gear including the Bagnall-Price and the Baguley. They also used marine (circular) fireboxes on narrow gauge engines, a design that was cheap but needed a different firing technique. Some of the designs of Kerr, Stuart and Co were brought to Bagnalls when they employed William Sydney Edwards, the Chief Draughtsman of Kerr Stuart and Co. Examples of such locomotives can be seen on the Sittingbourne and Kemsley Light Railway. In addition to locomotives, Bagnalls constructed rolling stock and trackwork enabling the complete equipping of light railways. In 1933 Bagnalls entered into an agreement with Deutz of Germany to manufacture their locomotives under licence using engines imported from Germany. In 1948 WG Bagnall Ltd was sold to the Bridge and Steelwork Company, Heenan and Froude, whose owner also owned The Brush Electrical Engineering Co Ltd of Loughborough and in 1951, Bagnalls formed an association with Brush to create Brush-Bagnall Traction Ltd. This association only lasted two years. Heenan and Froude sold Bagnalls to W H Dorman & Co in 1959 in exchange for Dorman ‘A’ shares.

The General Electric Company (GEC) merged AEI Traction Division and English Electric Traction in 1969 after acquiring both companies to create English Electric – AEI Traction Limited. The headquarters were located at Trafford Park in Manchester. This subsidiary company was renamed GEC Traction Limited in 1972.