The Ruston-Paxman Group was formed following the merger of Ruston and Hornsby with Davey, Paxman and Co Ltd in 1940. The constituent companies continued to trade under their original names, manufacturing traction and stationary engines. The company entered the rail traction market in the 1930’s and in 1950 they teamed up with British Thomson-Houston and the North British Locomotive Company to produce what became a ‘Type 1’ loco using their 16RPHXL engine, these engines were used in some other early British Rail prototypes. These, what were then relatively high speed (1500 rpm) engines, were not as reliable as the medium speed types and were not used in large numbers in the 1955 modernisation plan. A number of locomotives using two smaller engines were supplied to New South Wales and Western Australia railways. By 1961, the Group manufactured gas, oil, diesel and marine engines, gas turbines, diesel locomotives, boilers, steel tanks and vessels, pumps and pumping plants, rotary industrial filters and chemical plant, employing 10,590 people. The Group was acquired by English Electric in 1966, with their diesel interests becoming part of English Electric Diesels Ltd in 1968.

After incorporation into English Electric and then GEC the much more powerful 1500 rpm Valenta engines which had been developed in the meantime, mainly for marine applications, were incorporated in the British Rail ‘High Speed Train’. These were very successful and were produced in sufficient numbers to cover most of British Rail’s ’Intercity’ non electrified services. Similar trains were supplied to Australia. After over 20 years of intensive service the HST’s have been refurbished, some with Paxman VP185 engines, but most with an MTU engine. After the GEC - Alsthom merger, all the surviving diesel operations including Paxmans and Mirlees Blackstone which had been taken over in 1997 became Alstom Engines Ltd. In 1998 the company was sold to MAN B&W in 2000.