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atomic bomb or A-bomb, weapon deriving its explosive force from the release of nuclear energy through the fission (splitting) of heavy atomic nuclei.The first atomic bomb was produced at the Los Alamos, N.Mex., laboratory and successfully tested on July 16, 1945.tomic bombs were subsequently developed by the USSR (1949; now Russia), Great Britain (1952), France (1960), and China (1964). A number of other nations, particularly India, Pakistan, Israel, and North Korea now have atomic bombs or the capability to produce them; South Africa formerly possessed a small arsenal.
The program that developed the atomic bomb for the United States during World War II was the largest secret project ever undertaken by the U.S. government. The project was originally named Development of Substitute Materials, but there was concern that the name was too suggestive of its real purpose. section of land near Alamogordo, in south-central New Mexico was chosen and code-named Trinity. On July 16, 1945, the world entered the nuclear age with the detonation of the first atomic bomb. The explosion created a crater which measured nearly 2,400 feet across and was equivalent to about 20,000 tons of TNT.