What was the name of the secret U.S. project that developed the atomic bomb?

The Manhattan Project was the secret U.S. project during World War II that aimed to develop the atomic bomb. Initiated in response to fears that Nazi Germany might be working on similar weapons, the project brought together some of the country's top scientific minds, including notable physicist J. Robert Oppenheimer. Its success culminated in the first nuclear tests in 1945, ultimately leading to the bombings of Hiroshima and Nagasaki. The project was named after the Manhattan District of the U.S. Army Corps of Engineers, which oversaw the project's early stages. This historical context underscores the project's significance in wartime technology and its profound implications for international relations in the post-war era.

The other choices, while significant in their own contexts, do not pertain to the development of the atomic bomb. Operation Overlord refers to the Allied invasion of France, Project Blue Book was a U.S. Air Force program investigating UFOs, and the Atomic Energy Commission was formed after the war to oversee nuclear energy and weapons but was not involved in the initial development of the atomic bomb itself.