You could really write a treatise on the subject; the story is really one of the history of industrialization in the US from circa 1870 on up to the war and involves the location of natural resources like coal and iron ore and the placement of ports and railroads. It should also be noted that significant new capacity was built during the war as well. Ford's Willow Run plant outside Detroit (it built B-25s) was built from scratch in 1942 and was the largest industrial manufacturing facility in the world; current I-94 west from Detroit to Ypsilanti was built so workers could get there. Aircraft plants were built at Wichita, KS and Oklahoma City; Kaiser built shipyards on the West Coast. What made it all go was the production of steel, centered in Pittsburgh, but with major facilities in Youngstown, Birmingham, AL, Allentown and Gary, IN. Iron ore came from the Iron Range in Minnesota and was transported on the Great Lakes directly to the plants (why Gary was built) or to Cleveland and other ports for rail transport. Much of the auto industry, which was centered in Detroit but had assembly plants from coast to coast and parts suppliers all over the place, was converted to other forms of war production. Tanks, aircraft, military vehicles and other forms of materiel came out of what had been auto plants. The conversion of the US economy to war production was the one time in US history where it had a command economy, which was dedicated completely to producing war materiel. There was really no corner of the economy which was not affected, from heavy industry, to timber, to energy, to textiles and clothing manufacture, to agriculture. It was total economic commitment of all sectors of the US economy.