"On August 6, 1945, we enjoyed a tranquil morning with the end of the air-raid sirens that had continued far into the night, never dreaming that the fateful moment of 8:15 a.m. was approaching. Relieved to have gotten through the night without an attack, I resolved to put myself into the day's work. I was also excited at the thought of my wedding just three days off. So I dressed quickly, and when my family too had prepared for the day, my mother suggested we leave early while the air was still cool. But just as we were about to leave, the siren blared again."
This is a quote from Harry Truman's announcement to a dozen members of the Washington press corps when he was returning from the Potsdam conference:
"Sixteen hours ago an American airplane dropped one bomb on Hiroshima, an important Japanese Army base. That bomb had more power than 20,000 tons of TNT. ...The Japanese began the war from the air at Pearl Harbor. They have been repaid many fold. ...It is an atomic bomb. It is a harnessing of the basic power of the universe."
Dr. Michihiko Hachiya lived through the atomic bombing of Hiroshima on August 6, 1945. He kept a diary of his experience. This is an excerpt from that diary.
"Suddenly, a strong flash of light startled me - and then another. So well does one recall little things that I remember vividly how a stone lantern in the garden became brilliantly lit and I debated whether this light was caused by a magnesium flare or sparks from a passing trolley..."
This is a brief account of the mission's weaponeer, Comdr., now Capt., F. L. Ashworth, U.S.N., who was in technical command of the bomb and was charged with the responsibility of insuring that the bomb was successfully dropped at the proper time and on the designated target.
"The bomb burst with a blinding flash and a huge column of black smoke swirled up toward us. Out of this column of smoke there boiled a great swirling mushroom of gray smoke, luminous with red, flashing flame, that reached to 40,000 feet in less than 8 minutes. Below through the clouds we could see the pall of black smoke ringed with fire that covered what had been the industrial area of Nagasaki."

This is a newspaper from August 6, 1945 that was printed after Hiroshima was bombed.
One of the other reasons why Truman decided to drop the atomic bomb was because he was trying to scare the Soviet Union. In the August 15, 1960 issue of U.S. News and World Report James F. Byrnes was interviewed and asked: “Was there a feeling of urgency to end the war in the Pacific before the Russians became too deeply involved?” and he responded: “There certainly was on my part, and I’m sure that, whatever views President Truman may have had of it earlier in the year, that in the days immediately preceding the dropping of the bomb his views were the same as mine- we wanted to get through the Japanese phase of the war before the Russians came in.”