In September 1938, the world was again on the brink of war. Nazi Germany demanded to annex a large part of its neighbour Czechoslovakia. Czechoslovakia's allies thought that by betraying it to Hitler, they would keep the peace. They were wrong.
Five months later, two publications in scientific magazines declared that atoms of the chemical element Uranium were successfully broken into smaller atoms by being hit with neutrons, a process which also released significant energy. The authors of the two separate publications were actually one team of scientists who worked together for many years, but two members, Lise Meitner and Otto Robert Frisch, were Jews, who had to escape from the violent persecusion of Jews in Nazi Germany, as did other prominent Jewish physicists who previously worked in Germany, including the most prominent of them all, Albert Einstein.
Nazi Germany was not sorry to see some of the world's brightest scientists escape. The scientific breakthroughs made in nuclear physics, starting with Einstein's 1905 "theory of relativity", were so revolutionary, and so advanced, in comparison with classic physics, and the contribution of Jewish scientists in that field so prominent, that many in the German academic community, and in the Nazi regime, considered the whole thing as "Jewish Physics", false science. They were wrong.
Most of the physicists in Britain at that time were already pulled into the military research and development effort, focusing on new technologies as RADAR. The few who could still devote their time to nuclear physics, where those who lacked security clearance, including the Jewish refugees from Nazi Germany. During 1939 and early 1940, Frisch, who was "stuck" in Britain because of the war, and German-born Rudolf Peierls, worked on the practical calculations of what it would take to actually create an atomic bomb. It was originally assumed by most physicists that many tons of Uranium would be needed for a bomb, making it impractical as a weapon. But Frisch and Peierls correctly calculated that if the rare Uranium 235 isotope of Uranium will be used, then just a few kilograms of it would be enough to create a chain reaction, a bomb. They also correctly calculated the explosive power of such a bomb as equivalent to "several thousand tons of dynamite".
A year after the discovery of "Nuclear Fission", in March 1940, Frisch and Peierls wrote their findings in a memorandum that was passed to Sir Henry Tizard, the head of Britain's air defense related scientific research. This led to the creation of a committee to evaluate the "Military Application of Uranium Detonation" (MAUD). A second method for creating an atomic bomb was then suggested by scientists which fled occupied France. The 2nd method did not require extracting the rare Uranium 235 from the natural Uranium metal. Instead, it suggested to convert some of the natural Uranium to Plutonium, which would then be separated from the Uranium, and which could also produce chain reaction.
Over a year of scientific and industrial evaluation and research had passed, when on July 15, 1941, with Hitler's victorious army advancing towards Moscow, and the USA still trying to remain isolated from the war, the British MAUD committee delivered its final report. It said that an atomic bomb was feasible (and detailed methods and costs), and that it was urgent, because it was believed that Germany, where nuclear fission was discovered, was working on such a bomb. In response, the British atomic bomb project, code named "Tube Alloys", was started.
While the USA was still isolated from World War 2, there was minimal progress there. On August 2nd, 1939, six months after the published discovery of nuclear fission in Uranium, and just before World War 2 started in Europe, three Hungarian Jewish physicists, who previously participated in nuclear physics research in German universities, and then fled from German Nazism to the USA, decided that the US president must be warned of the danger that Germany will develop an atomic bomb. They approached Albert Einstein, the world's most famous physicist, and convinced him to join them in warning the president. The Einstein–Szilard letter reached president Roosevelt, who started a secret advisory committee on the subject with a token budget of $6,000. Later, in the summer of 1941, meetings between British and American physicists helped speed things in the US nuclear research and political decision making. In October 1941 president Roosevelt approved an American nuclear bomb development project, to be managed by the US Army.
The American and British atomic projects were combined. The US Army Corps of Engineers' project leadrship was located at an office in Manhattan, New York, which gave the entire project its unofficial but well known name, the Manhattan Project. The project progressed, still somewhat slowly, until Vannevar Bush, the head of the US Office of Scientific Research and Development, decided that aggressively efficient leadership was required, and on Spetember 23, 1942, Leslie Groves, an Army engineer who distinguished himself in overseeing the initial construction of the Pentagon, was appointed to command the Manhattan Project.
The production of an atomic bomb was scientifically feasible, but the task still ahead was immense, both in scale, and in difficulty. The main tasks of the Manhattan Project were to :
Under Groves' and Oppenheimer's leadership, the immense project overcame all the difficulties, and in less than three years it produced three atomic bombs. One was used in a live test, on July 16, 1945, which produced an explosion equivalent to 20,000 tons of explosives. The other two, one Uranium 235 bomb and one Plutonium bomb, were dropped on two Japanese cities, Hiroshima and Nagasaki, and practically levelled them, killing most of the population either by blast, heat, radiation, or radiation pollution which continued to kill people years later. In response, the shocked Japanese leadership surrendered, and World War 2 finally ended.
German Secret Weapons