I think I’ll do some reading, because honestly, even after watching shows explaining it, I just barely began to follow. I understand that a trigger kind of like a gunshot was needed to start the reaction for the 2 A bombs in Japan. Then I think two types of materials mingle and cause the reaction.
Like I said, I have some reading to do later.
Better late to the party than never. Today we are spoiled, we can Google what used to send us to the encyclopedias.
Considering the lack of modern computational resources (though there were strenuous efforts to mechanize calculations for the sake of military purposes) what took place in the early and mid decades of the 20th century was amazing.
Two sub-critical masses were used and a conventional explosive forced them together creating a single critical mass of fissionable material.