As for the USA, yes, holy shit, but it was also a country almost uniquely capable of achieving such a feat. Even more incredible is that it did that without even severely affecting the standard of living of its citizens, unlike the other countries, which all introduced very intense civil production rationing to pull off their more modest increases.

In the case of the USSR, fighting for its life and already an economy that barely focused on civil well-being, the doubling of war production and associated war expenses caused a gigantic famine in the immediate post-war years, while also causing massive suffering during the war years, and this aside from the brutalities introduced by the German invasion.

Also, I strongly recommend a couple books here: First: "The Wages of Destruction: The Making and Breaking of the Nazi Economy" by Adam Tooze

Second (truly a unique book that looks at the world's biggest war with a focus entirely on how people in different parts of the fighting countries ate and avoided starvation) "The Taste of War: World War Two and the Battle for Food " by Lizzie Collingham.

Even today common US citizens themselves cannot comprehend the scale involved. There are some interesting YouTube videos on the bonkers production efforts [1] [2] [3] [4] [5] that give some other angles of perceiving the scale. By 1944, fully 44% of the US GDP was devoted to wartime production, starting from an already-formidable economic base that many already recognized back in the 1930's despite the US' comparatively feeble industrial showing in WW1. Among the more famous leaders who recognized this massive industrial potential before WW2 even started were Yamamoto and Churchill.

Just as astonishing as the scale was the rapidity. The US military before WW2 was objectively not a top 10 rank by nearly any metric one cared to employ. This shifted practically overnight with substantive progress measured in months.

To really geek out over some of the critical numbers, check out this page [6].

Looking back, it gave me an intuitive grasp of just how much of the manufacturing sector the US bled out to the PRC, and even then, US manufacturing is still no slouch on the world stage.

[1] https://www.youtube.com/playlist?list=PLfMrqOdrCidQ2gpuSIxW0...

[2] https://www.youtube.com/watch?v=ncgQ33yu7Cc

[3] https://www.youtube.com/watch?v=6at-eJfJOgI

[4] https://www.youtube.com/watch?v=BExMOol11LA

[5] https://www.youtube.com/watch?v=PTtR1hqpnwU

[6] https://www.ww2-weapons.com/military-expenditures-strategic-...

I never really tried to find out (well I tried but not too hard) but in my opinion this was the part of what later made 'American Dream' (tm) come true:

The enormous, trained work force no longer needed after the war at the plants where they worked for the war effort started to move out over the whole country, bringing their knowledge and families with them. Combine it with a surplus of parts, machine tools (hot rods with aircraft engines as an extreme example) which allowed to prop the small business everywhere. And also this allowed for many people of color to get a standing in life (random exceprt to confirm my opinion):

>> After the war. When Black, Hispanic, and Native American soldiers returned they found a country that still did not grant them full rights, but a movement for the expansion of civil rights had been born. Some black soldiers who had left farm jobs in the South decided not to return home. Instead, they moved to cities, looking for work that was similar to what they had learned in the armed forces. This movement represented an intensification of the black migration that began around the turn of the century.

>> Birdie Farr's husband, John, worked as an airplane mechanic during the war and wanted to work on cars after it. His war work was vital to keeping bombers in the air. Like many black veterans, John had trouble finding similar work when he returned home. John applied for a mechanic's job at a York, Nebraska, auto dealership. The owner said he wouldn't hire him as a mechanic, but he'd hire him to clean up the shop. John said, "That isn't what I went to school for or come out of the service for. I want a real job." John had to work at odd jobs in the York area. Eventually, he took a job at the auto dealer, running the car wash until he worked his way into a job as a mechanic. John Farr worked as a specialty mechanic for 22 years before he started his own auto business in York.

>> Birdie credits the war with helping break up discrimination. "The war broke up a lot of that prejudice," she says. "You were there to do a job. And if you can do it, you're going to do it not matter what color you are. You work next to the next guy. Your life depended on him regardless of what color they are."

This is certainly true. Comparatively though, rationing in the U.S was nowhere near as bad as it was even in Britain, never mind the Reich, any other European country or much less the Soviet Union and Japan. These latter two placed millions of their people on near starvation rations and imposed extreme cutbacks in even the most basic civilian "luxury" goods. The Nazis were remarkably consistent about feeding their own people well (though with steadily decreasing food quality) but they pulled this off by literally starving vast other areas of Europe.

One of the books I recommend in a reply further down "The taste of war" goes into deep, carefully referenced detail on the food rationing by country, and even with their cutbacks, Americans had it incredibly better than any other country involved in the war, by far. It truly was quite impressive.