The Manhattan Project timeline
The atomic bombings of Hiroshima and Nagasaki capped six years of top-secret work by scientists from Europe and North America. Here is a summary of that process, including the Soviet Union's first atomic test four years later.
- 1939 :
Albert Einstein signs a letter warning US president Franklin D. Roosevelt of the destructive potential of nuclear fission, which was discovered by the German chemist Otto Hahn. The letter says the process could result in "extremely powerful bombs of a new type". Roosevelt creates the Advisory Body on Uranium.
- 1941 :
December 7: Japanese warplanes destroy much of the US Pacific fleet based at Pearl Harbor. The next day, the United States enters World War II.
- 1942 :
June: The US launches the Manhattan Project, a top-secret programme to develop an atomic bomb. More than two billion dollars are spent to achieve that goal.
- 1943 :
February: Robert Oppenheimer is named scientific director of a secret lab at Los Alamos, New Mexico, that is to build the bomb. The project includes top physicists from the United States, Britain and Canada, in addition to several who fled from the Nazi occupation of their homelands in Europe.
- 1944 :
November: US officials draw up a list of Japanese cities that could be the target of an atomic bomb. At the top of the list is Japan's seventh largest city, Hiroshima. Kyoto is rejected as a target owing largely to its historic and cultural importance.
- 1945 :
March 9-10: US warplanes carry out massive firebombing attacks on Tokyo and other major Japanese cities. Around 100,000 people die in the capital alone.
March 26: The battle of Okinawa begins. More than 200,000 Japanese soldiers and civilians die over the next three months while 12,000 US soldiers are also killed. The battle is used by US officials to justify using atomic bombs since an invasion of mainland Japan is presumed to carry an even higher cost.
April 12: Roosevelt dies and Harry Truman becomes president of the United States. He learns of the Manhattan Project on April 25.
May 8: Germany surrenders but fighting continues in Asia and the Pacific.
May-July: Components of the atomic bombs are shipped to Tinian, an island in the Marianas chain from where B-29 bombers are able to reach Japan.
July 16: At 5:30 am the "Trinity" test takes place near Alamogordo, New Mexico, demonstrating the awesome power of an atomic bomb and marking the dawn of the nuclear age.
At some point in July, Truman approves a mission to drop an atomic bomb on Japan.
July 26: In the Potsdam Declaration, Britain, China and the United States warn Japan that it must surrender or face "prompt and utter destruction".
July 28: Japan decides to "ignore" the ultimatum, although the word used -- mokusatsu -- also translates as "no comment".
August 6: The US B-29 bomber Enola Gay drops a 9,000-pound atomic bomb on Hiroshima at 8:15 am, killing 140,000 people by the end of December, according to a generally accepted toll. Truman tells Japanese leaders that if they do not surrender, "they may expect a rain of ruin from the air, the like of which has never been seen on this earth."
August 8: The Soviet Union declares war on Japan.
August 9: A second atomic bomb explodes over Nagasaki at 11:02 am, killing 74,000 people.
August 15: Japanese Emperor Hirohito tells his nation it has lost the war. He remains on the throne during post-war reconstruction of the country.
- 1949 :
August 29: Four years after Hiroshima and Nagasaki are destroyed, the Soviet Union successfully tests its own atomic bomb in Kazakhstan and becomes the world's second nuclear power.