1939-1950   1951-1970   1971-1980   1981-1990   1991-2000   2001   2002   2003   2004

August 2, 1939
Albert Einstein writes President Franklin D. Roosevelt, alerting the President to the importance of research on nuclear chain reactions and the possibility that research might lead to developing powerful bombs. Einstein notes that Germany has stopped the sale of uranium and German physicists are engaged in uranium research.

September 1, 1939
Germany invades Poland. World War II begins.

December 7, 1941
The Japanese attack Pearl Harbor. The United States enters the war.

January 19, 1942
President Roosevelt approves production of the atomic bomb following receipt of a National Academy of Sciences report determining that a bomb is feasible.

June 17, 1942
President Roosevelt instructs the Army to take responsibility for construction of atomic weapons complex. The Army delegates the task to the Corps of Engineers, which establishes the Manhattan Engineer District.

September 19, 1942
Brigadier General Leslie R. Groves, head of the Manhattan Engineer District, selects Oak Ridge, Tennessee, site for facilities to produce nuclear materials. Isotope separation of uranium235 takes place in the gaseous diffusion plant built in the K-25 area of the site, in the electromagnetic plant in the Y-12 area, and in the liquid thermal diffusion plant. A pilot pile (reactor) and plutonium separation facility are built and operated at the X-10 area.

November 25, 1942
Groves selects Los Alamos, New Mexico, as site for separate scientific laboratory to design an atomic bomb.

December 2, 1942
Metallurgical Laboratory scientists led by Enrico Fermi achieve the first self-sustained nuclear chain reaction in pile constructed under the west grandstand at Stagg field in Chicago.

January 16, 1943
Groves selects Hanford, Washington, as site for full-scale plutonium production and separation facilities. Three reactors--B, D, and F--are built.

April 12, 1945
President Roosevelt dies. Harry S. Truman becomes President.

May 7, 1945
Germany surrenders.

July 16, 1945
Los Alamos scientists successfully test a plutonium implosion bomb in the Trinity shot at Alamogordo, New Mexico.

August 6, 1945
The gun model uranium bomb, called Little Boy, is dropped on Hiroshima, Japan.

August 9, 1945
The implosion model plutonium bomb, called Fat Man, is dropped on Nagasaki, Japan. Five days later, Japan surrenders.

June 14, 1946
Bernard Baruch presents the American plan for international control of atomic research to the United Nations. The Soviet Union opposes the plan, rendering it useless.

August 1, 1946
President Truman signs the Atomic Energy Act of 1946.

January 1, 1947
In accordance with the Atomic Energy Act of 1946, all atomic energy activities are transferred to the newly created Atomic Energy Commission.

June 23, 1948
Soviet Union begins blockade of West Berlin.

August 29, 1949
Soviet Union detonates first atomic device.

January 31, 1950
President Truman instructs the Atomic Energy Commission to expedite development of a thermonuclear weapon.

June 25, 1950
North Korea invades South Korea. The Korean War begins.

October 9, 1950
President Truman approves a $1.4 billion expansion of Atomic Energy Commission facilities to produce uranium and plutonium for nuclear weapons.

Last Reviewed: 12/4/2007