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-...
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.