In 1936, and aswel as the Shadow Factories that existed, an extensive network of tunnels began construction. 
Longbridge was commissioned for an underground factory, which was built underneath Groveley Lane, where aircraft engines and associated components were assembled during WW2. 
By March 1940 tunnels were constructed to link other parts of the works site. These underground tunnels were capable of accommodating 10,000 workers mainly in the South Works.

 

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