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Conclusion

Thousands of Americans and immigrants from many countries contributed to the Manhattan Project, the product of an urgent resolve to develop the nuclear technology necessary to complete an atomic bomb before Nazi scientists could do the same.

The global threat was real, and the world was watching. Never before had such an extensive, expensive, technologically advanced and scientifically unprecedented effort commenced, on U.S. soil or anywhere else.

A top-secret project from its inception, the Manhattan Project employed more than 130,000 men and women who each contributed to a mysterious mission that they knew very little about, other than it was essential to the war effort—and that everyone's contribution mattered.

Visit the Manhattan Project National Historical Park at Oak Ridge, Los Alamos and Hanford. Experience the history. Take the tour at each historic site, and discover the secrets of the Manhattan Project.

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The war has ended party.
Image of Albert Einstein working on the manhattan project.
1939
  • Germany invades Poland, starting World War II. German physicists split a uranium atom.
  • Legitimate fears of potential Nazi super weapons spread internationally. The U.S. remains neutral.
  • Einstein and Fermi (an Italian-American physicist) warn President Roosevelt of the nuclear risk.
Image of a warship at dock.
1941
  • Japan attacks Pearl Harbor, killing 1,500. The United States declares war on Japan and Germany.
Image of an airstrip during world war 2
1942
  • Fermi leads the first controlled nuclear chain reaction at Stagg Field, University of Chicago
  • The Manhattan Project, a secret effort to build an atomic bomb, begins under Gen. Leslie Groves.
  • Groves approves “Site X” in Tennessee for uranium enrichment. Oak Ridge construction begins.
Military checkpoint during World War II
1942
  • Groves and physicist Robert J. Oppenheimer designate “Site Y” at Los Alamos, New Mexico.
  • Oppenheimer runs Los Alamos laboratory—the bomb research, development and design lab.
  • Absolute secrecy. No publicity. Public unaware. Workers unaware. VP Truman unaware at first.
Site construction is completed, and bomb design begins at Los Alamos, under Oppenheimer.
1943
  • Groves selects a 670-square-mile area in southern Washington State for “Site W” at Hanford.
  • Uranium enrichment begins at Oak Ridge’s X-10 graphite reactor and Y-12 plant.
  • Site construction is completed, and bomb design begins at Los Alamos, under Oppenheimer.
The X-10 graphite reactor at Oak Ridge reaches criticality, becoming self-sustaining.
1943
  • Nuclear sites readied at Oak Ridge, Tennessee; Hanford, Washington; Los Alamos, New Mexico.
  • Oak Ridge enriches uranium. Hanford manufactures plutonium. Los Alamos designs bombs.
  • President Roosevelt designates all three nuclear sites as military districts.
  • The X-10 graphite reactor at Oak Ridge reaches criticality, becoming self-sustaining.
First enriched uranium (200 grams of U-235) is delivered to Los Alamos, from Oak Ridge.
1944
  • First enriched uranium (200 grams of U-235) is delivered to Los Alamos, from Oak Ridge.
  • Hanford’s plutonium-239-producing Reactor B reaches criticality, becoming self-sustaining.
Hanford delivers the first plutonium-239, used in the “Fat Man” bomb, to Los Alamos.
1945
  • Hanford delivers the first plutonium-239, used in the “Fat Man” bomb, to Los Alamos.
  • European theater of WWII ends with Hitler’s suicide in Berlin and Germany’s surrender.
  • Refusing surrender, Japanese fight to the death or commit suicide in multiple large battles.
  • Following the firebombing of scores of Japanese cities, Allies plan a mainland invasion.
Invasion estimates predict 1-4 million Allied casualties and 5-20 million Japanese deaths.
1945
  • Invasion estimates predict 1-4 million Allied casualties and 5-20 million Japanese deaths.
  • Japan prepares, backing 2.3 million troops with civilian militia of 28 million men and women.
  • Pacific battles continue. Potsdam Declaration again demands unconditional Japanese surrender.
  • Japan ignores ultimatum despite threat of “prompt and utter destruction.” War continues.
The first nuclear test is conducted with a bomb detonation near Alamogordo, New Mexico.
1945
  • Long-ranged U.S. Boeing B-29 Superfortress heavy-bomber airplanes reach combat readiness.
  • The first nuclear test is conducted with a bomb detonation near Alamogordo, New Mexico.
Japan surrenders to the Allies aboard the USS Missouri in Tokyo Bay, ending WWII.
1945
  • “Little Boy” is dropped on Hiroshima, which is 70% destroyed. Japan refuses to surrender.
  • “Fat Man” is dropped on Nagasaki, which is 44% destroyed. More bombs are readied.
  • Japan surrenders to the Allies aboard the USS Missouri in Tokyo Bay, ending WWII.
U.S. sustains 1.25 million casualties killed or injured throughout the entirety of WWII.
1945
  • Total Japanese death toll from both bombs ranges from 129K to 226K+; a majority are civilians.
  • U.S. sustains 1.25 million casualties killed or injured throughout the entirety of WWII.
  • An estimated 60-80 million people die in WWII, the most deadly conflict in human history.
 The Manhattan Project ends, after spending $2B ($27B in 2017) and employing 130K Americans.
1946
  • The Manhattan Project ends, after spending $2B ($27B in 2017) and employing 130K Americans.
  • 90% of MP cost = building facilities, producing fissile material. 10% = weapons production.
  • New weapons testing and development continues at Bikini Atoll w/ Operation Crossroads.
The Atomic Energy Commission assumes nuclear weapons development control from the military.
1948
  • The Atomic Energy Commission assumes nuclear weapons development control from the military.
  • A new network of national laboratories dedicated to large scale “Big Science” is ushered in.
  • The nuclear era creates lifesaving isotopes for medical, biological, industrial, agricultural research.
Departments of Interior and Energy establish the Manhattan Project National Historical Park.
2015
  • Departments of Interior and Energy establish the Manhattan Project National Historical Park.