The Problem With the Hiroshima Bomb

The problem of assembling these materials was the main way that the bomb was a problem, if you will. They had to figure out how to make these materials assemble rapidly enough so they didn't start a chain reaction prematurely in which case they would melt down. So famously one of the problems that almost sunk the program occurred in 1944 in the spring when the first big production reactors in Washington State started producing plutonium from the reactors.