In 1903 W.H.Dorman produced their first internal combustion engine for the early motor car industry; this became the main activity of the company.
During the First World War the company was made a Controlled Establishment under the Conditions of War Act and made a notable contribution to the war effort, especially in the development of aerial warfare.
In 1929 Dorman began to move part of the plant to a new 20-acre site on Tixall Road, Stafford. By 1939 the manufacture of engines for road use had ceased and the company began to concentrate on the production of industrial and marine engines.
In 1939 the Ministry of Labour requisitioned the Foregate works for use as a training centre for engineers. The remainder of the plant transferred from Foregate Street to Tixall Road.centrate on the production of industrial and marine engines.
In 1959 W.H.Dorman bought the old established Stafford engineering firm of W.H.Bagnall’s Ltd.
W.H.Dorman was taken over by the English Electric Company in 1961 and by 1979 Dorman Diesels Ltd. was a subsidiary of GEC producing Dorman Diesel engines at Stafford and at the old Ruston & Hornsby factory in Lincoln.
The Dorman diesel engine business was bought in 1987 by Broadcrown and was later purchased by the Perkins Engines Company of Peterborough in 1993.
The last Dorman branded engine was produced in 1995.
In 1998 Perkins sold the Ruston & Hornsby range to RHL Spares Ltd following the closure of Dorman Diesels Central Spares Division in Lincoln. Formed by a group of experienced former Dorman employees to support the Ruston & Hornsby and Dorman Diesel engine ranges; RHL purchased the stock and rights to exclusively support the old Ruston & Hornsby range of engines. The RHL Spares business was purchased in 2006.
In September 2010 Perkins Engines agreed to sell all Dorman Diesels non-SE related parts business including the ST, DA,Q, J, L, LS, P, Y, Monair, F, and DWD engine ranges.