shadow factory
noun1
UK, Historical An aircraft factory in the World War II era, partly staffed by people from the motor industry, that was kept hidden from enemy aircraft.
- [...] but common prudence demanded, even before the outbreak of war, that details should not be disclosed which might reveal to a potential enemy the positions of "shadow factories" and air bases, and the location of stores of munitions, petrol, food, and so forth.1939 November, Charles E. Lee, “Railways and the War — I”, in Railway Magazine, page 313: