Timeline of Building Atomic Bombs
Scientists flee Europe to escape the rise of Hitler and fascism.
Otto Hahn and Fritz Strassmann discover the process of fission in uranium.
Eugene Wigner and Leo Szilard went to find Einstein on vacation, urging him to write a letter to Roosevelt about the dangers of Germany’s possible use of nuclear fission research.
July 16, 1939
Albert Einstein writes President Franklin D. Roosevelt, alerting the President to the importance of research on chain reactions and the possibility that research might lead to developing powerful bomb
August 2, 1939
Alexander Sachs discusses Einstein’s letter with President Roosevelt. Roosevelt decides to act and appoints Lyman J. Briggs head of the Advisory Committee on Uranium.
October 11, 1939 - October 12, 1939
Roosevelt informs Einstein that he has set up a committee to study uranium.
October 19, 1939
The Uranium Committee meets for the first time.
October 21, 1939
The Uranium Committee recommends that the government purchase graphite and uranium oxide for fission research.
November 1, 1939
The Uranium Committee receives permission to explore construction needs and cost to build a bomb with the Army.
October 9, 1941
Roosevelt approves production of the atomic bomb.
January 19, 1942
Researchers begin arriving at Los Alamos.
Los Alamos, New Mexico is selected as the bomb laboratory. Robert Oppenheimer is chosen as laboratory director.
November 25, 1942
Scientists led by Enrico Fermi achieve the first self-sustained nuclear chain reaction in Chicago.
December 2, 1942
Bomb design work begins at Los Alamos.
Bomb models are tested at Los Alamos.
A major reorganization to maximize implosion research occurs at Los Alamos.
Los Alamos receives it first plutonium.
February 2, 1945
Los Alamos scientists successfully test a plutonium implosion bomb.
July 16, 1945
Truman informs Stalin that the United States has tested a powerful new weapon.
July 24, 1945
The gun model uranium bomb (Little Boy) is dropped on Hiroshima, Japan.
August 6, 1945
The implosion model plutonium bomb (Fat Man) is dropped on Nagasaki, Japan.
August 9, 1945