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When the United States dropped the atomic bomb on Hiroshima, Japan in August of 1945 the world entered a new era.

The initial killing power of the weapon was like nothing anyone had ever seen before, and its long-term effects were more horrible than what most could imagine. And beyond the destructive strength that the bomb has, perhaps it is most powerful in the political forum. But for all the complicated problems that arose after its use, the basic design of the bomb nicknamed Fat Man was deceptively simple.

Inside a hard metallic casing were basically three important parts: a sphere of uranium with a cone-shaped piece missing, a cone-shaped piece of uranium and a gun to fire it with. When the bomb was detonated the gun fired the cone into the sphere, and set off the reaction that changed the world. The nature of atomic weaponry made the use of a radioactive substance (uranium) necessary.

Radioactive elements can, under certain conditions, break down at the most basic level and release a great deal of energy. When the cone met the sphere, the uranium reached critical mass, the amount of uranium needed to start the reaction. At this point, one part of one uranium atom broke away from the force that kept it part of the atom, collided with another atom and split it.

The parts that split from this atom then collided with others, setting off a chain reaction that released the energy responsible for the initial damage and death caused by the bomb. The use of a radioactive element in the bomb caused great amounts of radiation to be released into the atmosphere, which was responsible for many of the subsequent deaths attributable to the atomic bomb.

The scientific principles behind the atomic bomb seem very simple now, but the making of the atomic bomb by the United States was a very time consuming and expensive undertaking. On the 2nd August 1939 some scientists wrote to President Roosevelt of efforts in Nazi Germany to purify Uranium-235, which might in turn be used to build an atomic bomb.

It was shortly thereafter that the United States government began the serious undertaking known only then as the Manhattan Project. The Manhattan Project was designed to research and production that would produce a usable atomic bomb. The Project was named after the Manhattan Engineer District of the US Army Corps of Engineers, because a lot of the early research was done in New York.

In 1942 General Leslie Grove was chosen to lead the project. He bought a site at Oak Ridge, Tenn. for facilities to separate the necessary uranium-235 from the much more common uranium-238. Robert Oppenheimer was appointed to lead the day to day running of the project.

The team of scientists who worked on the atom bomb worked 6 days a week and often 18 hours a day. By 1945 the project had nearly 40 laboratories and factories which employed 200,000 people. That was more than the total amount of people employed in the US automobile industry in 1945. The total cost of the Manhattan project was $2-billion which is about the equivalent of $26 billion today. The cost was great, but many believe that had the United States not had atomic capabilities when it did, others would have beaten the US to the punch. The cost of this would certainly have been greater than anything that could be measured in dollars and cents.