In the first episode we will try to understand how the decision to drop the bomb on Hiroshima was reached, retracing the steps from 1943, the year in which the best minds in physics, such as Oppenheimer and Fermi, gathered at Los Alamos to test the first bomb. The experiment was successful and, during a summit meeting between Truman, Churchill and Stalin, the idea of using this new bomb against Japan began to spread. We will follow with Alberto Angela all the phases of the complex operation, from the preparation to the transport of the atomic bomb to the Tinian base, from where the mission to Hiroshima departed; at the same time we will also follow the advance of the Americans in the Pacific which was the scene of ferocious fighting between sea and sky.