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http://en.wikipedia.org/wiki/Supermarine_Spitfire#Production_dispersal

During the Battle of Britain, concerted efforts were made by the Luftwaffe to destroy the main manufacturing plants at Woolston and Itchen, near Southampton. The first raid, which missed the factories, came on 23 August 1940. Over the next month, other raids were mounted until, on 26 September 1940, both factories were completely wrecked,[91] with 92 people being killed and a large number injured; most of the casualties were experienced aircraft production workers.

Fortunately for the future of the Spitfire, many of the production jigs and machine tools had already been relocated by 20 September, and steps were being taken to disperse production to small facilities throughout the Southampton area.
POD
Suppose Lord Beaverbrook takes the first raid in the Southampton area as a more pressing matter and moves all production, development and design to dispersed sites at once (large scale dispersal to some 60 different sites starting up work again by September 1940). This would retain the type 317 four engine bomber design and the twin engine heavy fighter design equipped with six cannon. Also the aircraft production workers would increase build and training capacity at a vital point in wartime production. The downside is reduced stocks of Spitfires, Walruses, etc. up to September 1940.

The drawing office in which all Spitfire designs were drafted was relocated to another purpose-built site at Hursley Park, near Southampton. This site also had an aircraft assembly hangar, with its associated aerodrome, where many of the prototype and experimental Spitfires were assembled and flown.[92]

Four towns and their satellite airfields were chosen to be the focal points for these workshops:[91]

* Southampton and Eastleigh Airport
* Salisbury with High Post and Chattis Hill aerodromes[nb 7][94]
* Trowbridge with Keevil aerodrome
* Reading with Henley and Aldermaston aerodromes.

Completed Spitfires were delivered to the airfields on large Commer "Queen Mary" low-loader articulated trucks, there to be fully assembled, tested, then passed on to the RAF.
As usual, I'm more interested in points of view on impact of this than full blown time lines.
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