The explosion of the first two atomic bombs in Hiroshima and Nagasaki in 1945 marked the end of the Second World War, but its history dates years back into the past. Albert Einstein's theory of relativity equation gave scientists around the world the first ideas about creating an atomic bomb by the chain reaction of the atomic fusion of uranium. Albert Einstein was never involved directly in the construction of the bomb; yet, in 1939, at the beginning of Second World War, he sent a letter to United State's President Roosevelt urging him to build the bomb because Nazi Germany had developed a method to split the uranium atom. Later the United States Government implemented a project to develop the atomic bomb called "The Manhattan Project". It was a race against the clock to see who creates the bomb first, United States or Germany. Robert Oppenheimer was head of the Manhattan Project which was implemented in "Los Alamos" Lab, New Mexico. The most difficult task endured by the Manhattan Project was isolating the Uranium 235 which was a needed nuclear reactor in order to make the bomb work. In those times, this process was very difficult and it ought to be done mechanically with the help of centrifuges. This process is called uranium enrichment and was done on separate factories installed in Oak Ridge, Tennessee. Harold Urey from Columbia University and Ernest Lawrence from University of California were in charge of this important part of the project. After years of hard and coordinated work, on July 16, 1945, the first atomic chain reaction was tested in the northern mountains of New Mexico. The detonation was great and the characteristic mushroom like cloud could be seen from miles. The geographic features were obliterated. United States had won the race against Germany and now was time to use it in warfare.