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Predecessor Deasy Motor Company
Founded 1910
Founder(s) J D Siddeley
Headquarters Coventry, England
Products automobiles

Siddeley-Deasy was a British automobile, engine and aircraft company based in Coventry in the early 20th century. It was central to the formation, by merger and buy-out, of the later Armstrong Sideleley Motor and Armstrong Whitworth Aircraft companies.


The Deasy Motor Company was founded by Henry Hugh Peter Deasy in the factory that had previously been used to manufacture Iden cars. Deasy left in 1908 following disagreements with his Chief Engineer.[1] The company changed its name from Deasy to Siddeley-Deasy after J D Siddeley joined the company from Wolseley in 1910.[2]

Siddeley-Deasy grew rapidly using Rover chassis and Daimler and Aster engines. During World War I, Siddeley-Deasy grew to have 5,000 workers producing ambulances and aircraft engines which included the Puma, a water cooled straight-6 and the Tiger. The latter was a water cooled V-12, basically two Pumas on a common crankshaft.[3] They were one of six companies to produce the Royal Aircraft Factory R.E.8 aircraft from 1916. In 1917 three staff from the Royal Aircraft Factory joined Siddeley-Deasy and began to design fixed-wing aircraft.[4] Theye were S.D.Heron, an engine designer, F.M.Green, who became the chief engineer, and John Lloyd, who became chief aircraft designer. These last two stayed with Siddeley Deasy and its successor for many years. During 1917-18 the team led by Lloyd had designed three aircraft, one of which, the Siskin, was to become well known.

After the war, conditions for manufactures were difficult, and in 1919 Siddeley suggested[5] a merger with Armstrong-Whitworth who had been a supplier of Siddeley-Deasy engine castings. Armstrong Whitworth had themselves made aircraft, chiefly designed by Frederick Koolhoven who left the company in 1917 and then by F.M Murphy, but by 1919 they had decided to abandon aircraft manufacture and shed the associated staff. The merger in May 1919 initially produced an Armstrong Whitworth subsidiary called the Armstrong Whitworth Development Co. Ltd, which in turn produced its own subsidiary, Armstrong Siddeley Motors Ltd, essentially the old Siddeley-Deasy Company. Armstrong-Siddeley produced radial aircraft engines throughout its life, together with turbojets after the war. In April 1920 or slightly later, it produced its own subsidiary, The Sir W.G. Armstrong Whitworth Aircraft Co. Ltd. This last company went on to produce the Armstrong Whitworth Siskin aircraft in large numbers, together with all the later Armstrong Whitworth designs.

In March 1927, John Siddeley bought the parent Armstrong Whitworth Development Co. Ltd. and its subsidiaries from Armstrong Whitworth, renaming it the Armstrong Siddeley Development Co. Ltd. The name of the aircraft subsidiary, Sir W.G. Armstrong Whitworth Aircraft Co. Ltd. remained the same. The two key members of the Siddeley Deasy design team stayed with the reamed company for many years. John Lloyd was chief designer until 1948 and retired as technical director in 1959. F.M. Green retired in 1933.



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References / sources

  1. Tapper p.11
  2. Tapper p.12
  3. Tapper p.114
  4. Tapper p.15
  5. Tapper p.17-8


  • Tapper, Oliver (1973). Armstrong Whitworth Aircraft since 1913. London: Putnam Publishing. ISBN 0 370 10004 2. 

External links

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