“The Manhattan Project” – the nuclear weapons project in the U.S.A. – was the code name the Americans gave the nuclear weapons development project, which was centered in Los Alamos. Britain and Canada also assisted in the project. The Project’s Director was General Leslie Groves and its Scientific Director was Dr. Robert Oppenheimer. Some of the greatest scientists of that era, physicists, chemists, mathematicians and others, participated in the project, and among them many Jews, including some who had escaped from Europe and the terror of Nazi rule in Germany, who held key positions in the project, including its management. The powerful process of splitting the nucleus of the atom was starting to become clear at the end of the 1930’s. A physicist of Jewish descent and native of Austria, Dr. Lise Meitner, published this first, in a report in February, 1939. Three physicists, Edward Teller, Leo Szilard and Eugene Wigner, also Jews, who had come to the U.S.A. from Hungary, feared that this process, of splitting the atom nucleus, its knowledge available to German scientists, would be exploited by the Nazi regime to develop an extremely powerful bomb. They convinced Albert Einstein, also a physicist of Jewish descent, and native of Germany, already famous then thanks to his achievements, to warn President Roosevelt about this danger. Einstein did that in a letter from 2 August 1939, subsequent to which the President directed to intensify research in the U.S.A. in the area of Nuclear Physics, which signaled the beginning of the secretive “Manhattan Project” to produce a nuclear bomb. The U.S.A.’s entry into the war following the Japanese bombing of Pearl Harbor brought an acceleration of this process. Construction of the plants that will house production of the raw materials necessary to build an atomic bomb began in early 1942. One of the first was an experimental nuclear reactor. It was built by Enrico Fermi, a scientist of Italian descent, at the University of Chicago, and was activated by means of natural Uranium (not enriched) as the nuclear fuel and Graphite as the moderator, where, in 1942, a controlled process of a nuclear chain reaction was achieved for the first time. The principle centers where the project was conducted were the Los Alamos Laboratories in the State of New Mexico, where weapons were developed; the Oak Ridge Laboratories in the State of Tennessee, where the process of Uranium enrichment was accomplished; the Hanford Plant in the State of Washington, where the production of Plutonium was carried out; and laboratories in leading Universities, such as the metallurgic laboratory at the University of Chicago, the University of California, Berkeley, Columbia University and others, whose scientists also supported the project. Simultaneously, preparations were being made in the U.S. Air-Force to deliver the bomb and drop it on the target by B-29 bombers. At its peak in 1945, about 130,000 people were working on the project. The process of building the bomb was conducted in two parallel tracks, Uranium and Plutonium, and it was concluded in 1945 with the production 3 bombs, one of which, that had been produced in Hanford on the basis of Plutonium, was tested on 16 July 1945 in a ground experiment in the New Mexico desert near Alamogordo (code-named “Trinity Site”), and two others that were dropped on Japanese cities, the first on Hiroshima and the second on Nagasaki. The bomb that was dropped on Hiroshima on 6 August, whose code-name was “Little Boy”, was based on Uranium-235, which is a rare Uranium isotope and had to be separated from the Uranium-238 isotope. The bomb that was dropped on Nagasaki on 9 August, whose code-name was “Fat Man”, was based on Plutonium-239, an artificial element produced from Uranium-238 that was discovered by American scientists in the middle of 1942. “The Manhattan Project” was one of the biggest and one of the most secret projects of World War II and its success turned the U.S.A. into the first nuclear power in the world.