There are two types of atom bombs or atomic bombs: fission bombs (or uranium or plutonium based nuclear bombs) and fusion bombs or hydrogen bombs. Fission bombs were developed before fusion bombs and the United States was the first country to do so. The fission bombs were developed under a project called the Manhattan Project, in collaboration with Canada and the United Kingdom. The project was chaired by J. Robert Oppenheimer, who was a physicist. The very first atomic bomb was field tested in New Mexico, in July 1945 (under the code name of Trinity Test). Only two nuclear bombs have ever been used in a war and the bombing of Hiroshima and Nagasaki in 1945 (with nuclear bombs codenamed Fat Man and Little Boy) effectively ended the war with Japan. Since then several countries (including Soviet Union, United Kingdom, France, China, India, Pakistan, etc.) have successfully made and tested their own nuclear weapons.
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