It had been known since about 1900 that the natural decay of radioactive elements produced quantities of energy that were enormous compared to those produced by chemical reactions. The problem was that natural processes liberated it very slowly; for example, the half-life of radium is 1602 years, so a lump of radium will stay warm for thousands of years, but is not warm enough to be a useful source of energy. In 1914, [[H.G. Wells]] wrote a science-fiction novel describing "atomic bombs," in which the release of energy had been artificially speeded up; his description of the process was, however, imaginary gobbledegook. In 1933, Hungarian-born physicist [[Leo Szilard]] invented the idea of the nuclear ''chain reaction'' which made the rapid release of atomic energy a theoretical possibility. The idea was in the air, and in fact during the Second World War, Japan, Germany, and the United States all worked on atomic bomb projects, although the Japanese and German projects did not get far.
[[Leo Szilard]], who had immigrated to the United States, was determined to persuade President [[Franklin Roosevelt]] to fund the building of an atomic bomb.<ref>http://www.dannen.com/ae-fdr.html</ref> He felt that a letter to the President by [[Albert Einstein]] would help. Einstein, a pacifist, was better-known better than most physicists. Einstein agreed to sign a letter written by Szilard, which was then taken to President Roosevelt in early August 1939. The letter explained the feasibility and importance of developing an atomic bomb.
But President Roosevelt did little based on this letter, and instead only allocated a tiny $6,000 for such a project. Over two years passed without progress. It was not until Dec. 6, 1941, the day before Pearl Harbor, that an all-out effort to build an atomic bomb began under the direction of General [[Leslie Groves]]. This was what became known as the Manhattan Project.