https://www.construction-physics.com/p/how-to-build-300000-airplanes-in
Producing the aircraft needed to win the war required a complete transformation of the aircraft industry. Between 1939 and 1944, the value of aircraft produced annually in the U.S. increased by a factor of 70, and the total weight of aircraft produced (a common measure of aircraft industry output) increased by a factor of 64. In 1940, the airframe industry employed just 59,000 people; three years later that reached 939,000, with another 339,000 building aircraft engines. Factories of unprecedented size, enclosing millions of square feet were built; by the end of the war aircraft engine factory floor space had increased from 1.7 million square feet to 75 million, and a single large engine factory encompassed more space than had been used by the entire pre-war engine industry.