Events
December 7, 1941: Japan bombs Pearl Harbor
and the United States enters World War II.1942: Physicist J. Robert Oppenheimer becomes
director of the Manhattan Project.May 7, 1945: Germany agrees to unconditional
surrender, ending the war in Europe.July 16, 1945: The United States successfully
detonates the worlds first atomic bomb at the
Trinity test site in the desert of New Mexico.August 6,1945: The first atomic bomb to be used as a weapon is dropped on Hiroshima, Japan, at
approximately 8:15 a.m. Nicknamed Little Boy, the bomb is released from the Enola Gay, a B-29
bomber piloted by Brig. Gen. Paul Tibbets. It explodes 2,000 feet above ground, killing 80,000
people instantly. One of the main arguments for use of the bomb by U.S. officials is that it would
force Japan to surrender unconditionally.August 9, 1945: An atomic bomb is dropped over Nagasaki, Japan, by a B-29 bomber piloted
by Maj. Charles Sweeney. It explodes 1,540 feet above the ground. The original target for
the bomb, nicknamed Fat Man, is Kokura, Japan. Due to cloud cover, the bomb is instead
detonated over Nagasaki, the alternate location. It is estimated that 75,000 people are
killed immediately.August 9, 1945: Three days after the Hiroshima bombing, President Truman speaks to the
nation in a radio address: The world will note that the first atomic bomb was dropped on
Hiroshima, a military base. By this time, the United States had already dropped its second
bomb on Nagasaki.August 15, 1945: Japan surrenders, ending World War II.August 2, 1939: Albert Einstein sends a letter
to President Roosevelt describing the feasibility of
atomic power, the potential use of atomic bombs,
and a warning that Germany is already
working on atomic research.March 28, 1941: American
scientists conclude that
plutonium can be used as a weapon.December 6, 1941: President Roosevelt authorizes the
Manhattan Project to develop atomic weapons, a U.S.
government program formed to secretly build and test
an atomic bomb. The project originally began to counter
Nazi Germany.December 2, 1942: Enrico Fermi and his team at
the University of Chicago produce the world’s
first controlled and sustained nuclear fission reaction.March 1943: Construction of the bomb begins
on The Hanford Site, in Washington State.August 1, 1945: A typhoon approaching Japan
prevents launching an attack with Little Boy.
Several days are required for weather to clear.July 31, 1945: The assembly of Little Boy is
completed. It is ready for use the next day.July 26, 1945: President Truman issues the Potsdam Declaration, which warns Japan of
"prompt and utter destruction" and requires unconditional surrender of the Japanese
armed forces.July 29, 1945: The Japanese government rejects
the Potsdam surrender demand.August 4: Tibbets briefs the 509th Composite Group about the impending attack. He reveals
that they will drop immensely powerful bombs, but the nature of the weapons is not revealed.
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