The inventions were partly understood mechanistically- just like ML. What we didn't understand was the consequences of deployment (such as massive radiation leaks due to testing, unpredictable yields, the risks of global thermonuclear war, and the ongoing cost of maintaining a fleet of nuclear weapons).

Similar issues with molecular biology- we knew how to clone a gene from one organism to another, but that doesn't mean we really knew all the things going on (side effects) or what the large-scale implications are (hence the Asilomar agreement).

Even cars- while engines were understood mechanistically, it took quite some time for people to appreciate why automobile safety glass was necessary.

See the experiences learned during testing nuclear weapons- we tested them because we didn't understand them mechanistcally, at least not fully enough to predict many effects.