Depuis Krugman : http://krugman.blogs.nytimes.com/
After reviewing evidence from the 1940-41 editions of Business Week, Fortune, and The New York Times, Gordon and Krenn document that the American economy went to war starting in June 1940, fully 18 months before Pearl Harbor. In February 1941 fully one percent of the American labor force was at work building army training camps for 1.4 million new draftees. Employment in ship-building to expand the U. S. Navy and to supply Lend-Lease aid to Britain accounted for another one percent of the labor force in 1941. As early as June 1941, capacity utilization had reached 100 percent in the production of iron and steel and durable goods of all types.

And they show that during the period before capacity constraints were hit, the multiplier was actually fairly high.

Effectivement les indicateurs économiques des US notent la montée de la production *avant* l’entrée en guerre avec le Japon, le fait est donc à savoir pour l’expliquer.