In August 1945, two US Army Air Force B-29 bombers each dropped single "atomic bombs" on the Japanese cities of Hiroshima and Nagasaki. Little Boy and Fat Man each exploded with energies equivalent to more than 10,000 tons of conventional explosive. Just seven years later, in October 1952, the Ivy Mike test saw the detonation of America's first full-scale thermonuclear weapon that achieved a yield over 400 times as much as Little Boy and Fat Man. The invention of nuclear weapons was one of the most stunning scientific and technological developments of the 20th century. Carried out under the auspices of the United States Army's Manhattan Project, this development had profound immediate and long-term impacts: the bombings of Hiroshima and Nagasaki helped bring World War II to a close, but set the stage for the Cold War, nuclear proliferation, and fear of nuclear annihilation and terrorism.This volume, prepared by an acknowledged expert on the Manhattan Project, gives a concise, fast-paced account of all major aspects of the project at a level accessible to an undergraduate college or advanced high-school student familiar with some basic concepts of energy, atomic structure, and isotopes. The text describes the underlying scientific discoveries that made nuclear weapons possible, how the project was organized, the daunting challenges faced and overcome in obtaining fissile uranium and plutonium and in designing workable bombs, the dramatic Trinity test carried out in the desert of southern New Mexico in July 1945, and the bombings of Hiroshima and Nagasaki. The final chapter surveys current worldwide nuclear weapons deployments, and a bibliography lists sources of published and online information along with numerous links.