After Japanese leaders flatly rejected the Potsdam Declaration, President Truman authorized use of the atomic bomb anytime after August 3, 1945. On the clear morning of August 6, the first atomic bomb, nicknamed Little Boy, was dropped on the city of Hiroshima. Leveling over 60 percent of the city, 70,000 residents died instantaneously in a searing flash of heat. Three days later, on August 9, a second bomb, Fat Man, was dropped on Nagasaki. Over 20,000 people died instantly.