I have often wondered if we could build an Iowa class battleship today...and I think not. The unique, incrementally developed skills necessary to build something like that are likely lost to memory, and would have to be re-learned.
And that is just one example.
That is sobering.
Now, think about our nuclear deterrent and the aging scientists and the shrinking group of specialists who know anything about that. One day soon, there will be nobody to manage/fix that aging collection weapons. We don’t even build new nuclear plants anymore. Skill fields such as those are lost over time, if there isn’t a steady stream of new personnel.
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The same thing goes for the Saturn V moon rocket. It could not be built today for the same reasons you provided about Iowa class battleships, other lost, forgotten, technologies, skills.