I was under the impression that Heisenberg made a fundamental mistake on a back of envelope calculation of the amount of an important input required that led hi

I was under the impression that Heisenberg made a fundamental mistake on a back of envelope calculation of the amount of an important input required that led him to believe it was not a tenable option and therefore the project was eventually killed. that doesn't mean that we didn't just get very lucky and that he might have on the flipside gotten very close to building something