Stewart Fox was a laboratory helper at the University of Chicago's Metallurgical Laboratory ("Met Lab") during the Manhattan Project. He was part of the Special Engineer Detachment (SED) at the Met Lab.
Fox worked in the Chicago Pile 1 (CP-1) group. On December 2, 1942, he was on one of the forty-nine scientists, who witnessed the Chicago Pile 1 at Stagg Field become the world's first nuclear reactor to critical.
For more information about Stewart Fox and the Chicago Pile 1 Pioneers, please see the following reference: