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On August 6, 1945, the first bomb was detonated above the city of Hiroshima.

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Lieutenant General Leslie Richard Groves Jr. (17 August 1896 – 13 July 1970) was a United States Army Corps of Engineers officer who oversaw the construction of the Pentagon and directed the Manhattan Project

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The following summer he gathered together at Berkeley a small group of some of the best theoretical physicists in the country to talk about the actual bomb design. The group, which he dubbed the "luminaries," included Hans Bethe and Edward Teller. By the end of the summer they concluded that the bomb project would require a major scientific effort.

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In 1941, Robert Oppenheimer, an American nuclear physicist was brought into the atomic bomb project. His first task was to calculate the amount of uranium needed to sustain a chain reaction.

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With reorganization in place, the nature of the American atomic bomb effort shifted from one that was once dominated by research scientists to one in which scientists played a supporting role in the construction enterprise run by the U.S. Army Corps of Engineers.

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The Manhattan Project cost 2.2 billion dollars which is equivalent to $24.4 billion in today's economy.

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Statistical Review?World War II: A Summary of ASF Statistics

, Statistics Branch, Control Division, Headquarters, Army Service Forces, U.S. War Department, 1946, pp. 75-6. Cost data are for 1942-1945. The total cost to the United States for World War II was approximately $3.3 trillion.)

All bombs, mines and grenades — $31.5 billion

Small arms materiel (not incl. ammunition) — $24 billion

All tanks — $64 billion

Heavy field artillery — $4 billion

All other artillery — $33.6 billion

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The Manhattan Project was a desperate effort by the US to beat the Nazis to the development of a nuclear weapon. Since this task needed to be done with great urgency it required a huge effort by many people willing to sacrifice their time to produce technologies that would outpace the enemies.  The U.S. government was so adamant about this project special towns such as Oak Ridge and Hanford were specifically built for the project. The production of the bombs produced a furious push in the development of science, technology, engineering, military and the whole of society into a new age. It brought out the powerhouse that we see today as the United States of America, a country prior to the beginning of the war which was suffering from the Great Depression and then after the war coming out as the new super power of the world.

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In March 1942, with President Roosevelt’s approval, the Army Corps of Engineers started to partake in S-1 meetings, marking the beginning of the military’s participation in the matter.  S-1 was the code name for the Uranium Committee and the military’s involvement reflected the need for security within the program. This, coupled with the Corps' expertise in construction would be needed to build the production facilities required for making the atomic bomb. Now, an Army officer would be in overall command of the entire project.

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The Manhattan Project started in the fall of 1939. It was created when President Roosevelt became alert of the possibility that German scientists were racing to build an atomic bomb. This struck fear in Roosevelt leading him to set up the Advisory Committee of Uranium which consisted of both civilian and military representatives.

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In June 1940, Roosevelt established a voice for the scientific community by establishing the National Defense Research Committee. This was a reorganization of the Advisory Committee on Uranium into a scientific body that eliminated military membership. The creation of this new committee enabled more influence and more direct access to money for nuclear research. Some of the committee's early priorities were studies on radar, proximity fuzes, and anti-submarine warfare with continued isotope separation and chain reaction work.