Near the end of World War II, the United States dropped the first nuclear bomb ever used in warfare. The bomb was code named "Little Boy." The fission-type nuclear bomb exploded with the energy equivalent of approximately 13 kilotons of TNT. This article describes a 16 day model-based inquiry (MBI) unit on nuclear chemistry that investigates the detonation and continuing effects of "Little Boy." The main goal of the unit is to allow students to engage in modeling to construct a valid evidence based explanation for how fission releases radiation and how radiation affects the human body.