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The Manhattan Project was a research and development program during World War II that produced the first atomic bombs. It was launched in 1939 after the discovery of nuclear fission by German scientists. The project was led by the United States with the support of the United Kingdom and Canada. It involved more than 130,000 scientists, engineers, and other personnel, and cost nearly $2 billion (equivalent to about $28 billion today). The project was highly secretive, and even President Truman, who became President after Roosevelt's death in April 1945, did not know about it until two weeks after taking office. The first atomic bomb was successfully tested in Alamogordo, New Mexico, on July 16, 1945, and on August 6, the United States dropped an atomic bomb on the Japanese city of Hiroshima, killing an estimated 140,000 people.
The Manhattan Project was created as a response to the fear that Nazi Germany would develop an atomic bomb first and use it as a weapon during World War II. The project was mainly focused on producing a weapon that would help the Allies win the war. The project's scientific director, J. Robert Oppenheimer, was responsible for coordinating the work of various scientists, including Enrico Fermi, who successfully produced the world's first controlled nuclear chain reaction. The Manhattan Project's work was carried out in secret, and its existence was known to only a few high-level government officials. Even the workers who were part of the project were kept in the dark about the full extent of the program. The project's success in producing the atomic bomb was a turning point in world history, and it marked the beginning of the nuclear age, which brought about a new era of global political, military, and scientific challenges.