On December 28, 1942, United States president Franklin D. Roosevelt formally approved an investment in the top-secret project that would result in atomic bombs being dropped on the Japanese cities of Hiroshima and Nagasaki three years later, killing thousands of people. The approval of detailed plans for building production facilities was made after a series of more incremental decisions committing the nation to creating atomic weapons. Years in the making This research and development project moved slowly — in the late 1930s, there were anxieties that Nazi Germany might build an atomic bomb first, and the Manhattan Project became the...