<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Nuclear weapons possess enormous destructive power from nuclear fission or combined fission and fusion reactions . Building on scientific breakthroughs made during the 1930s, the United States, the United Kingdom and Canada collaborated during World War II, in what was called the Manhattan Project, to counter the suspected Nazi German atomic bomb project . In August 1945, two fission bombs were dropped on Japan, standing to date as the only use of nuclear weapons in combat . The Soviet Union started development shortly thereafter with their own atomic bomb project, and not long after that both countries developed even more powerful fusion weapons known as "hydrogen bombs". </P> <P> In the first decades of the 20th century, physics was revolutionised with developments in the understanding of the nature of atoms . In 1898, Pierre and Marie Curie discovered that pitchblende, an ore of uranium, contained a substance--which they named radium--that emitted large amounts of radioactivity . Ernest Rutherford and Frederick Soddy identified that atoms were breaking down and turning into different elements . Hopes were raised among scientists and laymen that the elements around us could contain tremendous amounts of unseen energy, waiting to be harnessed . </P> <P> H.G. Wells was inspired to write about atomic weapons in a 1914 novel, The World Set Free, which appeared shortly before the First World War . In a 1924 article, Winston Churchill speculated about the possible military implications: "Might not a bomb no bigger than an orange be found to possess a secret power to destroy a whole block of buildings--nay to concentrate the force of a thousand tons of cordite and blast a township at a stroke?" </P>

When did the development of nuclear science begin