The very first use of an atomic weapon in warfare was on August 6, 1945, when the United States Air Force dropped a bomb known as "Little Boy" on the Japanese city of Hiroshima. Then, just three days later, the U.S. Air Force dropped another bomb, dubbed Fat Man, on the city of Nagasaki. World War II had become focused on the Pacific theater, as Nazi Germany had surrendered in May. At the Potsdam Conference in July, the United States, United Kindom, and China issued a declaration required Japan's total surrender. The United States had also just tested an atomic bomb at the Trinity test. So when the United states promised "prompt and utter destruction," it was clear what that meant. The Japanese government refused to respond, so the Allies dropped bombs. In actuality, the atomic bombing of Hiroshima was unlike anything else ever seen before. Then, to reinforce the promise of "utter destruction," the U.S. took Japan's silence after Hiroshima as a go ahead to bomb another city. Nagasaki wasn't even the intended target. Yet it experienced the same kind of total destruction and the deaths of tens of thousands. And less than a week later, Emperor Hirohito had officially surrendered.