Feynman was recruited to join the Manhattan Project, the top-secret US government initiative to develop the atomic bomb during World War II. He was drawn to the project by the urgency and importance of the work, despite his initial reservations about nuclear weapons.

Feynman was stationed at the Los Alamos Laboratory in New Mexico, where he played a crucial role in the theoretical calculations and simulations necessary for the bomb's development. He worked alongside many of the leading physicists of the time, including Enrico Fermi, Robert Oppenheimer, and Hans Bethe.

At a young age, Feynman headed the theoretical computing group responsible for using IBM punch card machines to perform the calculations needed for the development of the atomic bomb. His ingenuity and resourcefulness were highly valued.

After the war, Feynman grappled with the moral implications of his involvement in the Manhattan Project. He recognized the destructive power of nuclear weapons and expressed concerns about their potential misuse. This experience deeply impacted his views on science and society.