Chicago Pile-1 was the first artificial nuclear reactor, built under the leadership of Enrico Fermi at the University of Chicago. It became operational on December 2, 1942, marking a significant milestone in the development of nuclear energy. The reactor was constructed using graphite as a moderator and uranium as fuel, allowing for a controlled nuclear chain reaction. The successful operation of Chicago Pile-1 demonstrated the feasibility of sustained nuclear reactions, paving the way for future research in nuclear physics and energy. This experiment was a crucial step in the Manhattan Project, which ultimately led to the development of atomic weapons during World War II.