I've found this to be a fascinating breakdown of the US's production capacity advantage in WWII:
http://www.combinedfleet.com/economic.htm> America, even in the midst of seemingly interminable economic doldrums, still had:
* Nearly twice the population of Japan.
* Seventeen time's Japan's national income.
* Five times more steel production.
* Seven times more coal production.
* Eighty (80) times the automobile production.
> Furthermore, America had some hidden advantages that didn't show up directly in production figures....the per capita productivity of the American worker was the highest in the world. Furthermore, the United States was more than willing to utilize American women in the war effort....The net effect of all these factors meant that even in the depths of the Depression, American war-making potential was still around seven times larger than Japan's, and had the 'slack' been taken out in 1939, it was closer to nine or ten times as great!
> ...
> By 1944, most of the other powers in the war, though still producing furiously, were beginning to max out their economies (i.e. production was stabilizing or plateauing). This resulted from destruction of industrial bases and constriction of resource pools (in the case of Germany and Japan), or through sheer exhaustion of manpower (in the case of Great Britain and, to an extent, the USSR). By contrast, the United States suffered from none of these difficulties, and as a consequence its economy grew at an annual rate of 15% throughout the war years. As scary as it sounds, by the end of the war, the United States was really just beginning to get 'warmed up.' It is perhaps not surprising that in 1945, the U.S. accounted for over 50% of total global GNP.
> ...
> But it is no joke to say that we were literally building ships faster than anybody could sink them, and still have enough left over to carry mountains of material to the most God-forsaken, desolate stretches of the Pacific. Those Polynesian cargo cults didn't start for no reason, and it was American merchant vessels in their thousands which delivered the majority of this seemingly divinely profligate largesse to backwaters which had probably never seen so much as a can opener before.