Students will learn about the role of African Americans in the Manhattan Project as scientists, technicians, and workers. They will examine fourteen scientists and technicians who contributed to the Manhattan Project. They will read biographies of these individuals and share their findings with the class. As an elaboration exercise, students will gain a better understanding of critical mass and how a nuclear reaction can become sustained. Students will be able to visualize what is meant by subcritical, critical, and supercritical masses. Note: This lesson plan works extremely well alongside the AIP Teacher’s Guide: African Americans and Life in a Secret City, which has students use oral histories and historical photographs to explore the living and working conditions for African Americans at Hanford, one of the sites of the Manhattan Project.