On Aug. 6, 1945, The Enola Gay, a specialized B-29 bomber, dropped an atomic bomb on the city of Hiroshima. Given the code-name "Little Boy," the bomb was the first nuclear weapon used in a war, a decision that came about after years of testing, debate and last-minute negotiations.
Jan. 19, 1942: President Franklin Delano Roosevelt approves construction of an atomic bomb
With the United States officially in World War II, President Roosevelt approves the construction of atomic bombs. In the summer of 1942, Col. James C. Marshall, director of the Laboratory for the Development of Substitute Metals, sets up the Manhattan Engineering District in New York City and the effort to create a viable atomic bomb would later become known as the Manhattan Project.
May 7, 1945: Scientists conduct the '100 Ton Test' at the Alamogordo Test Range
After creating a viable nuclear weapon, Manhattan Project scientists decide to calibrate their measuring equipment before testing this new device. The group then detonates more than 100 tons of TNT as well as tubes containing 1000 curies of fissionable materials at the Alamogordo Test Range in New Mexico.
Named after scientist Marie Curie, a curie is a unit of measure for radioactivity. By using nuclear material, the scientists and technicians attempted to gauge how far radioactive fallout would spread.
July 16, 1945: The successful testing of a plutonium bomb at the Trinity test site
At 5:29:45 a.m. Mountain War Time on July 16, Dr. J. Robert Oppenheimer, scientific head of the Manhattan Project, oversees the detonation of the 'Gadget,' a plutonium-based implosion bomb. The Gadget produces a destructive force equivalent to 20,000 tons of TNT.
July 26, 1945: The Potsdam Declaration is delivered to the Japanese government
During the Potsdam Conference in Germany, President Harry S. Truman, Soviet Premier Stalin and British Prime Ministers Churchill and Atlee meet to discuss World War II and its inevitable aftermath in Europe.
The Potsdam Declaration, a joint proclamation of the United States, Great Britain and China, is issued during the conference and delivered to the Japanese government. It calls for Japan's unconditional surrender and warns of "prompt and utter destruction" in the case of noncompliance.
July 28, 1945: Japan announces a position of 'mokusatsu'
Speaking to journalists on July 28, Prime Minister Kantaro Suzuki announces Japan's position of mokusatsu towards the Potsdam Declaration. Mokusatsu is a Japanese term that can be translated in various ways, including "ignore" or "refrain from any comment."
Based on the translation that they receive, the Allied forces believe that Japan is planning to ignore the terms of the Potsdam Declaration.
July 30, 1945: President Truman gives Secretary of War Henry Stimson the orders to bomb Hiroshima
After receiving information from Secretary of War Henry Stimson about the readiness of the atomic bombs, President Truman gives his approval to attack Hiroshima, but no sooner than Aug. 2.
Aug. 5, 1945: The Enola Gay is selected to drop the first atomic weapon
One of several special B-29 bombers designed to handle atomic weapons, the Enola Gay is selected for the first atomic mission that was code-named "Operation Centerboard I."
Aug. 6, 1945: 'Little Boy' detonates over Hiroshima
Under the command of Lt. Col Paul W. Tibbets, the Enola Gay releases the atomic bomb known as 'Little Boy' over Hiroshima, creating a blast that flattened most buildings within the city. Approximately 200,000 people died from radiation poisoning in the days, weeks and years that followed.
- Enola Gay
- Potsdam Declaration
- Secretary of War Henry Stimson
- dropped an atomic bomb
- Trinity test site
- President Harry S. Truman
- in World War II