The
United States was the first country in the world to develop
nuclear weapons, and is the only country to have used them in
war against another nation. During the
Cold War it conducted over a thousand
nuclear tests and developed many long-range weapon delivery systems.
[2] It maintains an arsenal of about 5,000 warheads to this day
[1], as well as facilities for their construction and
design, though many of the Cold War facilities have since been deactivated and are sites for
environmental remediation.
The United States of America first began developing nuclear weapons during World War II under the order of President Franklin Roosevelt in 1939, motivated by a fear that they were engaged in a potential race with Nazi Germany to develop such a weapon. After a slow start under the direction of the National Bureau of Standards, at the urging of British scientists and American administrators the program was put under the Office of Scientific Research and Development, where in 1942 it was officially transferred under the auspices of the U.S. Army and became known as the Manhattan Project. Under the direction of General Leslie Groves, over thirty different sites were constructed for the research, production, and testing of components related to bomb making. These included the scientific laboratory, Los Alamos (in New Mexico), under the direction of physicist Robert Oppenheimer, a plutonium production facility, Hanford (in Washington), and a uranium enrichment facility, Oak Ridge (in Tennessee).
By investing heavily both in breeding plutonium in early nuclear reactors, and in both the electromagnetic and gaseous diffusion enrichment processes for the production of uranium-235, the United States was able by mid-1945 to develop three usable weapons. A plutonium-implosion design weapon was tested on July 16, 1945 ("Trinity"), with around a 20 kiloton yield. On the orders of President Harry S. Truman, on August 6 of the same year a uranium-gun design bomb ("Little Boy") was used against the city of Hiroshima, Japan, and on August 9 a plutonium-implosion design bomb ("Fat Man") was used against the city of Nagasaki, Japan. The two weapons killed approximately 250,000 Japanese citizens outright, and thousands more have died over the years from radiation sickness and related cancers.
Between 1945 and 1990, more than 70,000 total warheads were developed, in over 65 different varieties, ranging in yield from around .01 kilotons (such as the man-portable Davy Crockett shell) to the 25 megaton B41 bomb.[3]
