With the creation of the Manhattan Project in August 1942, the U.S. government had an organization that could manage the complex and costly effort needed to build the atomic bomb. However, the practicality of the bomb still had to be proven. The first big step toward making the bomb a reality was taken in Chicago in an unused squash court. Here Enrico Fermi and Leo Szilard built the first working atomic pile. The pile was made of alternating layers of uranium and graphite blocks stacked or piled into a cube. The graphite was needed within the pile to slow down the bombarding neutrons so they could be absorbed by the nucleus of the uranium atoms. The pile also contained control rods made of cadmium that prevented a chain reaction until they were removed. On December 2, 1942, Fermi gave the order to withdraw the control rods...