As Alan Milward pointed out in his fascinating study of World War II production, the American economy not only produced the material and food needed to wage war and sustain its allies, it also enlarged during the contlict.
"Fighting on Our Own Ground: The War of Production, 1920-1942,"
Naval War College Review: Vol. 45
, Article 9.
Available at: http://digital-commons.usnwc.edu/nwc-review/vol45/iss2/9