Anyone else here highly skeptical of the publicly available stories about how nuclear bombs work?

A nuclear powder plant needs giant rods of U235, perfectly positioned covered under heavy water to be hit with an alpha emitter in order to start a nuclear reaction and only under these specific conditions will the reaction slowly start to grow and even then you are still losing some neutrons escaping from the reaction.

They actually expect us to believe that if you just slam two little balls of U235 together at high speeds there are going to be enough free neutrons already in the material to start the reaction, and grow it to the point were it causes a massive explosion big enough to take out a city?