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Manhattan Project

The Manhattan Project was the top-secret United States-led research and development program during World War II that produced the first atomic weapons.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

The Manhattan Project was the top-secret United States-led research and development program during World War II that produced the first atomic weapons. It involved major scientific, industrial, and military efforts in the United States, with support from the United Kingdom and Canada. The project culminated in the Trinity nuclear test in July 1945 and the atomic bombings of Hiroshima and Nagasaki in August 1945.

Origins

The Manhattan Project grew out of wartime concerns in 1939 and 1941 that nuclear fission research could be used to build weapons before Germany did. The project became formally organized in 1942 under the U.S. Army Corps of Engineers.

Major facilities

The best-known production and research centres were Los Alamos, Oak Ridge, and Hanford, each serving different roles in bomb design, uranium enrichment, and plutonium production. Other universities and laboratories also contributed to the effort.

Trinity and wartime use

The first nuclear test, Trinity, took place on 16 July 1945 in New Mexico and confirmed the feasibility of the plutonium bomb design. Two atomic bombs were then used against Japan in August 1945, ending the war in the Pacific.

Legacy

The project led to the nuclear age, changed military strategy and international politics, and helped shape the postwar U.S. nuclear establishment. It also contributed to the creation of national laboratories and remains a major subject in science and ethics history.

Key facts

  • The Manhattan Project was a top-secret U.S.-led wartime program that developed the first atomic bombs.
  • It was formally created in 1942 in response to fears that Nazi Germany might develop a nuclear weapon first.
  • Major sites included Los Alamos, New Mexico; Oak Ridge, Tennessee; and Hanford, Washington.
  • The Trinity test on 16 July 1945 was the first successful nuclear detonation.
  • The project marked the beginning of the nuclear age and remains a major subject in science and ethics history.
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Canadian context

Canada was part of the wider Anglo-American wartime collaboration on atomic research and production associated with the Manhattan Project, making the project relevant to Canadian military and scientific history.[10]

Frequently asked questions

What was the Manhattan Project?
It was the top-secret U.S.-led wartime program that developed the first atomic bombs during World War II.
Why was it called the Manhattan Project?
The name came from the Manhattan Engineer District, an Army Corps of Engineers administrative unit whose early offices were in Manhattan.
When did the Manhattan Project begin?
It was formally created in 1942, though its scientific and administrative origins trace back to work and planning in 1939–1941.
Where did the Manhattan Project happen?
Its major sites included Los Alamos, New Mexico; Oak Ridge, Tennessee; and Hanford, Washington.
What was Trinity?
Trinity was the first nuclear weapons test, conducted on 16 July 1945 in New Mexico.
What was Canada’s role?
Canada supported the Anglo-American atomic weapons effort and is part of the broader wartime collaboration associated with the project.

References

  1. National Park Service — https://www.nps.gov/mapr/learn/manhattan-project.htm
    Supports: Overview of the project, major sites, historical significance, and nuclear-age legacy
  2. Atomic Heritage Foundation — https://ahf.nuclearmuseum.org/ahf/history/manhattan-project/
    Supports: Project origins, official creation date, and wartime collaboration
  3. Encyclopaedia Britannica — https://www.britannica.com/event/Manhattan-Project
    Supports: Origins, naming, Trinity test, and historical background
  4. Encyclopedia of the History of Science — https://ethos.lps.library.cmu.edu/article/id/35/
    Supports: Description of the project as an Anglo-American wartime effort and a major megaproject
  5. National Park Service — https://www.nps.gov/mapr/learn/historyculture/timeline.htm
    Supports: Official project dates, workforce size, and duration
  6. The National WWII Museum — https://www.nationalww2museum.org/war/topics/manhattan-project
    Supports: Scale, secrecy, and wartime purpose of the project
  7. U.S. Department of Energy — https://www.energy.gov/lm/manhattan-project-background-information-and-preservation-work
    Supports: DOE’s institutional connection to the Manhattan Project and major sites
  8. Encyclopaedia Britannica — https://www.britannica.com/story/timeline-of-the-manhattan-project
    Supports: Timeline details, Los Alamos, first reactor, and overall scale