49 scientists and workers witnessed Chicago Pile-1, the world's first controlled, self-sustaining nuclear chain reaction, going critical on December 2, 1942. Four years later, 15 of those participants posed for an iconic photograph on the steps of Eckhart Hall at the University of Chicago. Below is a list of the men and women in that image, along with their years of birth and death. It is followed by a full list of the people who were present when CP-1 went critical.