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The Shadow Factories were a government initiative for the production of aero engines in 1936.
The factories were financed by H. M. Government and both shops and plant remained Government property but they were managed by the factories as agents.
Within a year five factories were set up and run by five motor car companies:
All the manufactured components were inspected by the Aeronautical Inspection Directorate. The first engine assembled from the composite parts underwent testing at the works of the Bristol Aeroplane Co.
The engine selected for production was the Bristol Mercury VIII, a fully supercharged nine cylinder air-cooled radial engine with a power output of 825 b. h. p. at 13,000ft, designed by Mr. A. H. R. Fedden. Two of these engines were installed in the Bristol Blenheim bomber.
Each firm specialised in different components of the engine. The Rootes (Humber) factory produced the crankcase rear cover, blower and accessories. The Daimler Company manufactured the crankcase, oil sump, priming system, and such like. The Standard Motor Co was responsible for the cylinder group, and the Rover Company at Tyseley, provides connecting rods, pistons, valves, and tappet gear. The Austin Company produced the crankshaft and the reduction gear, etc.