Robert E. Johnson was a research assistant at the University of Chicago's Metallurgical Laboratory ("Met Lab") during the Manhattan Project.
Johnson 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. A photograph of the Chicago Pile-1 members including Johnson (fourth row, left-most) at the twentieth anniversary appears on the left.
At the age of ninety-one, Robert E. Johnson died in Palos Park, IL on December 10, 2009.
For more information about Johnson and the Chicago Pile 1 Pioneers, please see the following reference: