The definitive, Pulitzer prize–winning account. I learned new things about the development of nuclear physics and of the industrial and managerial challenge of building and testing the bomb. For instance, creating the first critical pile of uranium was a serious technical challenge even after the basic physical theory had been worked out (you have to get very pure materials, build it in just the right shape, etc.) Another challenge was creating the critical mass quickly enough to release the energy all at once: put the pieces together too slowly, and the reaction fizzles out. The implosion method that accomplished this for the plutonium bomb was tricky: the charges had to be placed very precisely to get a uniform shell of inward force. The book also presents both the abject horror of the bomb’s effects on Hiroshima, and also the reasons why the US felt they had to use it—a fair treatment in my opinion.