In short
In 1942, the United States launched a secret weapons program to build the world's first atomic bomb before Nazi Germany could. Codenamed the Manhattan Project, it employed 130,000 people across multiple sites, cost $2 billion, and fundamentally altered the balance of global power—and the nature of warfare itself.
How it unfolded.
The five-minute version
What actually happened.
The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. The Manhattan Project employed nearly 130,000 people at its peak and cost nearly US$2 billion.
As it was happening
20 voices, 2149 days.
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Einstein's letter to Roosevelt
Albert Einstein signs a letter to President Franklin D. Roosevelt warning that Nazi Germany could develop atomic weapons, sparking initial U.S. interest in atomic research.
Voices from this moment (1)
Einstein's letter to Roosevelt
Oct 2
“Albert Einstein signs a letter to President Franklin D.”
As it was happening
20 voices, 2149 days.
Day 0 · October 2, 1939
Einstein's letter to Roosevelt
Albert Einstein signs a letter to President Franklin D. Roosevelt warning that Nazi Germany could develop atomic weapons, sparking initial U.S. interest in atomic research.
“Albert Einstein signs a letter to President Franklin D.”
- Einstein's letter to Roosevelt, Oct 2
Day 796 · December 6, 1941
Feasibility confirmed
The National Academy of Sciences report concludes that a nuclear chain reaction is theoretically possible, validating the scientific basis for a weapons program.
“We are engaged in the most important scientific endeavor of…”
- U.S. Army Corps of Engineers internal briefing, March 1942, Mar 15
“The physics works.”
- Synthesized from period accounts - conversations with colleagues, 1942-1943, Jun 1
“The National Academy of Sciences report concludes that a…”
- Feasibility confirmed, Dec 6
Day 989 · June 17, 1942
Manhattan Engineer District established
The U.S. Army Corps of Engineers officially creates the Manhattan Engineer District, with General Leslie Groves appointed to oversee the secret weapons program.
“This undertaking represents the War Department's most…”
- Synthesized from period accounts - Internal War Department memo, August 1942, Aug 10
“America's laboratories are mobilized as never before.”
- Synthesized from period accounts - New York Herald Tribune column, late 1942, Nov 1
“The U.”
- Manhattan Engineer District established, Jun 17
Day 1157 · December 2, 1942
First controlled chain reaction
Enrico Fermi achieves the first controlled nuclear chain reaction beneath Stagg Field at the University of Chicago, proving sustained nuclear fission is possible.
“Enrico Fermi achieves the first controlled nuclear chain…”
- First controlled chain reaction, Dec 2
Day 1277 · April 1, 1943
Los Alamos Laboratory opens
J. Robert Oppenheimer assumes leadership of the Los Alamos Laboratory in New Mexico, where bomb design and assembly will take place.
“We have accepted an enormous responsibility.”
- Synthesized from period accounts - Los Alamos inaugural address, April 1943, Apr 15
“J.”
- Los Alamos Laboratory opens, Apr 1
Day 2019 · April 12, 1945
Roosevelt dies
President Franklin D. Roosevelt dies; Harry Truman assumes the presidency and learns of the Manhattan Project for the first time.
“President Franklin D.”
- Roosevelt dies, Apr 12
Day 2114 · July 16, 1945
Trinity test
The first nuclear weapon is detonated at the Trinity test site near Alamogordo, New Mexico. Oppenheimer later recalls the moment by quoting the Bhagavad Gita: 'Now I am become Death, the destroyer of worlds.'
“The first nuclear weapon is detonated at the Trinity test…”
- Trinity test, Jul 16
Day 2135 · August 6, 1945
Hiroshima bombing
The B-29 bomber Enola Gay drops 'Little Boy' on Hiroshima, Japan. The explosion kills approximately 70,000 people instantly and over 140,000 by year's end.
“Secret Atomic Research Project Employs Thousands Across…”
- The New York Times, Aug 7
“Chicago's Role in Atomic Bomb Development Revealed”
- Chicago Tribune, Aug 8
“The B-29 bomber Enola Gay drops 'Little Boy' on Hiroshima,…”
- Hiroshima bombing, Aug 6
Day 2138 · August 9, 1945
Nagasaki bombing
A second bomb, 'Fat Man,' is dropped on Nagasaki, killing approximately 40,000 people immediately and over 70,000 by year's end.
“British Scientists Collaborated on Atomic Bomb, Government…”
- The Times (London), Aug 9
“Canada's Secret Role in Atomic Weapons Program Disclosed”
- The Globe and Mail, Aug 10
“A second bomb, 'Fat Man,' is dropped on Nagasaki, killing…”
- Nagasaki bombing, Aug 9
Day 2144 · August 15, 1945
Japan surrenders
Japan announces its surrender, effectively ending World War II. The atomic bombs are credited as a major factor in the decision.
“The Atom Unleashed: How America Built the Bomb”
- Time Magazine, Aug 20
“Japan announces its surrender, effectively ending World War…”
- Japan surrenders, Aug 15
Front pages.
3 outlets carried the story: The New York Times, Chicago Tribune, The Times (London).
Media coverage
What the world was reading.
5 pieces, ranked by how much they shaped the discourse.
The New York Times
Newspaper · United States · Aug 7, 1945
"Secret Atomic Research Project Employs Thousands Across Nation"
Synthesized from period reporting - The U.S. government has revealed the existence of a vast, secret atomic research program that mobilized nearly 130,000 workers across multiple states to develop nuclear weapons. The Manhattan Project, conducted under the tightest security protocols, represents the largest scientific undertaking in American history.
- Aug 20, 1945
Time Magazine
Magazine · United States
"The Atom Unleashed: How America Built the Bomb"
Synthesized from period reporting - Time's cover story dissects the unprecedented scientific mobilization that cost nearly $2 billion and transformed American industrial capacity. The Manhattan Project emerges as a defining technological achievement of the war effort.
- Aug 9, 1945
The Times (London)
Newspaper · United Kingdom
"British Scientists Collaborated on Atomic Bomb, Government Confirms"
Synthesized from period reporting - The British government acknowledges that leading scientists from the United Kingdom contributed substantially to the Manhattan Project alongside American researchers. The joint Anglo-American effort underscores the wartime alliance's commitment to developing atomic weaponry.
- Aug 8, 1945
Chicago Tribune
Newspaper · United States
"Chicago's Role in Atomic Bomb Development Revealed"
Synthesized from period reporting - The University of Chicago's Metallurgical Laboratory, working under the aegis of the Manhattan Project, was instrumental in achieving the first controlled nuclear chain reaction. The city becomes centerpiece of America's atomic weapons program revelation.
- Aug 10, 1945
The Globe and Mail
Newspaper · Canada
"Canada's Secret Role in Atomic Weapons Program Disclosed"
Synthesized from period reporting - Canadian scientists and uranium resources proved critical to the Manhattan Project's success, the government reveals. The dominion's contribution to atomic weapons development marks a pivotal chapter in wartime scientific cooperation.
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Sources & citations.
Sources
Where this came from.
Every claim on this page traces to a public, license-clean source. We don't asterisk well.
Wikipedia
1 source- 1.Manhattan Project
en.wikipedia.org