They insisted that Albert Einstein inform President Roosevelt about the possibility of the Germans making an atomic bomb. In late 1939, President Roosevelt ordered an American effort to make an atomic bomb before Germany. This project to produce the atomic bomb was named "The Manhattan Project- . Industrial and research activities took place all over the United States. J. Robert Oppenheimer led The Manhattan Project. Oppenheimer directed the design and building of the bomb. He and other scientists worked on this project from 1943 to 1945. The first atomic bomb was successfully exploded on July 16, 1945, near Alamogordo, New Mexico. .
President Roosevelt died on April 12, 1945. Vice President Harry S. Truman became President of the United States. On May 7, 1945 Germany surrendered. Truman proclaimed May 8 as V-E Day (Victory in Europe Day). In July, President Truman went to Potsdam, Germany, to discuss war issues with Prime Minister Churchill of Great Britain and Premier Stalin of the Soviet Union. During his time in Posdam, the President received secret word that the atomic bomb had been successfully tested. On his way back to the United States, President Truman ordered American fliers to drop an atomic bomb in Japan. .
On August 6, 1945, a B-29 bomber named Enola Gay left the Pacific island of Tinian to bomb the Japanese city of Hiroshima. The pilot, Colonel Paul Tibbets, named the Enola Gay after his mother. The crew of Enola Gay was told that no one could be sure what would happen when the atomic bomb was dropped over Hiroshima. The atomic bomb was named "Little Boy." The Enola Gay carried the "Little Boy" and 7,600 gallons of fuel that made it very heavy. No one was sure if the Enola Gay could be able to lift of the ground, so the final assembly of the bomb was done in the air. The bomb was dropped from an altitude of thirty-one thousand feet and detonated at 1,800 feet above the center of the city.