For all the studying and all the tests, they did not know for certain that they would survive the flight. It had never been done before. But the invasion of Japan was planned next and, for all the destruction this would wreak (and they did not yet know nor anticipate acute radiation syndrome), many more millions of people would surely die if the men in that plane did not take on this burden.
I mentioned once about my uncle’s role in WWII.
A fellow officer greeted my dad’s older brother in the mess hall that night with, “And what did you do today, soldier?”
“I think I just ended the war.”