America was unprepared for war militarily, but ready industrially. Underestimating how ready was the enemy's biggest wartime mistake. And they should have known. Even in 1938, U.S. national income was double the incomes of Germany, Japan and Italy combined. America produced five million new 1937 cars, while Japan produced 26,000.
Even so, at war's start American workers and resources were underutilized. Three million men were unemployed. Automobile plants were operating at 50%. The war ended the Depression, and the Depression made America—uniquely self-sufficient, with an industrial heartland far from attack—a national factory open and hoping for business.
A month after Pearl Harbor, FDR's "impossible" 1942 production goals, including 60,000 aircraft, 120,000 tanks, and 55,000 antiaircraft guns, were intended to energize America, and frighten the enemy. Organization was difficult. New production agencies conflicted with established military purchasing bureaus. With the Army alone ordering a quarter of a billion trousers and half a billion socks, military production threatened the quality of civilian life. Finally, by May 1943, the organization was in place to maximize American industrial might.
The big winners were the big corporations. 33 of them received half of all military contracting. General Motors alone supplied 1/10th of all war production. Corporate profits went from $6.4 billion in 1940 to $11 billion in 1944. Farmers did well too, as farm prices rose 50%. Due partly to overtime, average worker earnings rose 65%, as the war provided jobs for 3.2 million new job seekers and 7.3 million others (half of them women) who wouldn't have worked otherwise. The output per American worker hour was double that of Germany, five times that of Japan. Ford's Willow Run plant rolled out a B24 every hour; Kaiser built a Liberty Ship in four days, just to show it could. By January, 1944 America had a weapons stockpile that would give the Yanks a 3-to-1 advantage over the enemy, and supply 60% of all allied munitions. And that massive advantage meant fewer troops in combat—90 divisions, instead of the estimated 215—and therefore thousands of lives saved.
"The most important things in this war are machines," said Joe Stalin, "and the United States is a country of machines."
By war's end, America had produced 299,293 aircraft (Japan 70,000), 1,556 naval vessels, 5,777 merchant ships, 634,569 jeeps, 88,410 tanks (Germany, 44,000), 6.5 million rifles, 2,383,311 trucks and 40 billion bullets.