Manhattan Project

Manhattan Project, the name given to the United States effortstrongly aided by the United Kingdomto build the atomic bombs that helped end World War II (1939-1945). The Manhattan Project ranks as the largest industrial and scientific effort in the history of the world, costing more than $2 billion in 1945 dollars and involving more than 175,000 workers. All research and experiments were conducted in almost total secrecy. Only a relatively small number of people knew the exact purpose of the project, which created the most powerful weapon ever used.

The Manhattan Project ushered in a new

The Manhattan Project ushered in a new era in human history known as the Atomic Age. It demonstrated the feasibility of atomic energy for both peaceful and military uses. It also led to an arms race that, according to many scientists, produced enough nuclear weapons to destroy human civilization and end most forms of life on Earth. "See also "Arms Control; Nuclear Energy; Nuclear Weapons Proliferation.

The Manhattan Project began in 1942. It

The Manhattan Project began in 1942. It officially ended in 1946 when it became part of the Atomic Energy Commission (AEC). Originally based in Manhattan, a borough of New York City, the project eventually spread across the nation and was concentrated at three main sites located in Oak Ridge, Tennessee; Hanford, Washington; and Los Alamos, New Mexico. Its director was Brigadier General Leslie R. Groves. American physicist J. Robert Oppenheimer was the scientific director at Los Alamos, which attracted some of the most brilliant scientists and mathematicians of the 20th century. Among the scientists and mathematicians who participated in the Manhattan Project were Philip H. Abelson, Hans Bethe, Niels Bohr, Sir James Chadwick, Enrico Fermi, Richard Feynman, Otto Frisch, George Kistiakowsky, Ernest Lawrence, Philip Morrison, Seth Neddermeyer, John von Neumann, Rudolf Peierls, I. I. Rabi, Leo Szilard, Edward Teller, Stanislaw Ulam, Harold Urey, and Victor Weisskopf. Five of these scientists had already won Nobel Prizes when the project began, and three more would later go on to win Nobel Prizes.

The Manhattan Project produced four atomic

The Manhattan Project produced four atomic bombs. One was tested July 16, 1945, at a bombing range site known as Trinity near Alamogordo, New Mexico. Two others were dropped on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945. A fourth was ready for use in late August, but by then Japan had surrendered and World War II had ended.

Origins of the Manhattan Project

The origins of the Manhattan Project can

The origins of the Manhattan Project can be traced to the scientific laboratories of Britain and Europe in the early 1900s. At that time, the basic unit of matter, the atom, was viewed as solid and impossible to divide. The startling discoveries of radium; the X ray; the electron, proton, and neutron; and alpha, beta, and gamma rays, however, alerted scientists to the existence of a subatomic world. As British physicist Ernest Rutherford and Danish physicist Niels Bohr suggested, instead of being solid, the atom resembled a miniature solar system. Within the atom negatively charged electrons orbited positively charged protons and electrically neutral neutrons in the atom`s nucleus.

Scientists knew well that the atoms of

Scientists knew well that the atoms of each chemical element differed from one another. Hydrogen, which consists of one electron orbiting one proton, is the simplest. Scientists classify hydrogen with the atomic number one. Uranium, with 92 electrons orbiting a nucleus with 92 protons, is the most complex of the natural elements. It has the atomic number 92. In addition, these elements often contain variationscalled isotopesthat occur because they have different numbers of neutrons bound to the protons in the nucleus. For example, the element uranium has three isotopes, known by their atomic numbers, U238, U235, and U234. The numbers are derived by adding the number of protons in the uranium nucleus, 92, with the number of neutrons in the nucleus. U238 is the most common form of uranium; the rare U235 isotope forms only about 0.7 percent of naturally occurring uranium. Because uranium appeared to be an unstable element, scientists began to bombard it with streams of neutrons, hoping to discover a new form of energy.

The 1930s saw major breakthroughs in understanding

The 1930s saw major breakthroughs in understanding the atom. In 1933 Hungarian-born physicist Leo Szilard, who had fled Nazi Germany for England, was standing on a London street corner waiting for the light to change. Suddenly he realized that if the right material were found, splitting the nucleus of an atom could release neutrons and cause a nuclear chain reaction in which the released neutrons would cause more atoms to split, or fission. The result would be a self-sustaining series of fissions, causing a continuous release of nuclear energy. Such a chain reaction could be used to produce either electricity or a bomb. The next year Szilard filed a British patent on this subject, but kept it secret out of fear that German scientists might learn it was possible to make an atomic bomb.


Meanwhile, in 1933 in Paris, French scientists Irne Joliot-Curie and her husband Frederic Joliot discovered artificially created radioactivity. Shortly afterwards in Rome, Italian physicist Enrico Fermi created the first artificially created elements (beyond uranium). Fermi also split the atom, but at the time he did not realize what had occurred.

In Berlin

In Berlin, Germany, physical chemists Otto Hahn and Fritz Strassmann repeated Fermi`s experiments, bombarding uranium with neutrons. In late 1938 they were baffled when they found traces of barium in their results. Hahn wrote to his longtime scientific partner, Lise Meitner, to ask her opinion. Meitner was probably the foremost woman scientist of her generation. She had been forced to flee Germany due to the anti-Semitic laws enacted by the Nazi regime of Adolf Hitler ( "see "National Socialism). Meitner and her nephew, physicist Otto Frisch, concluded in a December 1938 discussion that the two German scientists had split the uranium atom`s nucleus virtually in half. As a result of splitting the uranium atom, barium with the atomic number 56 and krypton with the atomic number 36 were formed. Added together they represented the 92 protons in the uranium atom`s nucleus. Frisch was the first to name this process fission. (See the Sidebar with this article, The Discovery of Fission.)

Meitner and Frisch provided a theoretical

Meitner and Frisch provided a theoretical explanation for Hahn and Strassmann`s results and argued that the experiments confirmed Bohr`s model of the atom. When the uranium atom split or fissioned, it released an enormous amount of energy. How much energy could be calculated by using the famous formula of Austrian-born physicist Albert Einstein, "E"= "mc"2. In this formula "E" is energy, "m" is mass, and "c" is the speed of light squared. Since the speed of light300,000 kmsec (186,000 misec)is such a large number, very little mass is required to produce a great deal of energy. Moreover, if each fission released additional neutrons in the process, a nuclear chain reaction would be possible.

Meitner and Frisch raced to Copenhagen

Meitner and Frisch raced to Copenhagen, Denmark, to inform Bohr, who was preparing to leave for a physicists` conference in Washington, D.C., in January 1939. As soon as the scientists in Washington learned that uranium could be fissioned, several rushed to their laboratories to repeat the experiment. Within a year, more than 100 scientific papers had appeared on nuclear fission. When Szilard first heard the news of uranium fission, he predicted that the world was headed for grief. By 1939 a small group of scientists was well aware that a weapon of terrible power was possibleat least in theory.

The Building of the Atomic Bomb

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The British Effort

In early 1939 most nuclear scientists believed

In early 1939 most nuclear scientists believed that from 50 to 180 tons of natural uranium, containing only a tiny percentage of U235, would be required for a chain reaction to occur and an atomic bomb to be built. However, it was not practical to build a bomb weighing 50 tons. As a result most scientific research concentrated on other possible uses of nuclear energy, such as using uranium to operate large power plants or, perhaps, as power sources for ships or submarines. Then Nazi Germany invaded Poland on September 1, 1939, and Europe plunged into war. The scientists realized that any plans to build large-scale nuclear power plants would have to wait until the war was over.

Two weeks after the invasion of Poland

Two weeks after the invasion of Poland, Hitler made a radio speech in which he threatened Britain with a weapon against which there is no defense. British intelligence officers monitored this speech and came up with four possible interpretations: (1) Hitler was bluffing, (2) the Nazis had developed a deadly poison gas, (3) Hitler was referring to the German Air Force, the Luftwaffe, or (4) the Germans had developed an atomic bomb. In the fall of 1939 British intelligence could neither confirm nor deny the existence of a German atomic weapon. Thus, Prime Minister Winston Churchill decided that Britain should take no chances, and he instructed British scientists to investigate this possibility.

Because most of Britain`s scientists

Because most of Britain`s scientists were already occupied with other work, the job fell to two refugee German physicists who had fled Nazi Germany but were not yet British citizens: Otto Frisch and Rudolf Peierls. After intense study the two men produced the March 1940 Frisch-Peierls Memorandum. This brief scientific paper concluded that only the U235 isotope fissionedrather than the more abundant U238. Consequently, if U235 could be separated from U238, then only a relatively small amount of U235 would be needed for a chain reaction to occur. Fifty tons of natural uranium would not be required to make a bomb. Instead, a bomb could be made by utilizing about a kilogram of U235 (later revised upward to about 10 kg [22 lb]). Although it would be difficult, scientists could separate U235 from U238 using industrial techniques.

The two scientists warned

The two scientists warned, however, that Britain might not wish to use this bomb because of the radioactive fallout that would occur. Churchill`s government immediately formed a top-level committee to further examine the report. In 1941 this committee concluded that although the bomb program might cost as much as a battleship, Britain should pursue it. I wish I could tell you that the bomb is not going to work, British scientist Sir James Chadwick told two American scientists, but I am 90 percent certain that it will.

By 1940 British scientists viewed the possibility

By 1940 British scientists viewed the possibility of creating an atomic weapon with utmost seriousness. But German bombers could easily reach British targets, and Churchill knew that Britain could never build the gigantic factories necessary to produce such bombs. Any new building of that size would be quickly spotted and destroyed by the Luftwaffe. So the British effort remained largely at the theoretical level.

The U.S. Program

The U.S. atomic bomb program moved at a

The U.S. atomic bomb program moved at a somewhat slower pace. Early in 1939 various emigre scientists living in the United States steadily campaigned for increased U.S. nuclear research. They met so many obstacles, however, that they felt they were swimming in syrup, as the refugee Hungarian physicists Eugene Wigner and Leo Szilard put it. In July 1939 Szilard, Wigner, and another refugee Hungarian physicist, Edward Teller, conferred on the best way to gain the attention of the U.S. government. They decided on a plan to have the world`s most famous scientist, fellow refugee Albert Einstein, write a letter to President Franklin D. Roosevelt. The three men met with Einstein at his summer home on Long Island. Einstein later signed his name to a letter, dated August 2, 1939, that officially warned Roosevelt of a new type of bomb. Hidden in the hold of a ship, such a bomb could easily destroy a harbor city. At the time no one dreamed that an atomic bomb could ever be dropped from an airplane. (See the Sidebar, Einstein`s Letter to Franklin D. Roosevelt.)

Alexander Sachs

Alexander Sachs, an acquaintance of the scientists who was on familiar terms with Roosevelt, delivered the letter on October 11, 1939, a month after the Nazi invasion of Poland. Although Roosevelt knew little about science, he immediately established an Advisory Committee on Uranium to look into the matter. In June 1940 an even more important National Defense Research Committee came into being, followed by the Office of Scientific Research and Development on June 28, 1941. Still, the Americans never displayed the same fear or sense of urgency as the British until Japan attacked Pearl Harbor on December 7, 1941. Suddenly the United States was at war with Japan and Germany. With this, all discussion regarding an atomic bomb shifted from abstract theory to practical application: The nation that built the atomic bomb first would surely win the war.

In the months following Pearl Harbor

In the months following Pearl Harbor, the U.S. government completely reorganized its atomic bomb effort by enlisting the aid of the United States Army Corps of Engineers. The project shifted from a program dominated by scientists in university laboratories to a gigantic, nationwide construction project under the Corps of Engineers` Manhattan Engineer District (hence the name Manhattan Project). Brigadier General Leslie R. Groves, an able engineer who had helped build the Pentagon, assumed overall charge of the project. Groves insisted on a complete refocus for all nuclear research. All discussion of postwar power plants or individual power sources for airplanes, ships, or submarines had to cease. From then on, the project had only one goal: to create an atomic weapon to end the war in the shortest possible time.

Groves began by enlisting the aid of several

Groves began by enlisting the aid of several large American corporations, including Chrysler, General Electric, Eastman Kodak, Westinghouse, and DuPont. He also called on numerous universities, such as the California Institute of Technology in Pasadena, Columbia University in New York City, the University of Chicago, the Massachusetts Institute of Technology (MIT) in Cambridge, and the University of Rochester in New York, to conduct further nuclear research. Finally, he oversaw the creation of three gigantic federal installations at Oak Ridge, Tennessee; Hanford, Washington; and Los Alamos, New Mexico. The race to beat the Nazis to the secret of the atomic bomb had begun in earnest.

Groves did not assume control of the project

Groves did not assume control of the project until the fall of 1942, by which time the United States had been at war with the Axis powers for almost nine months. Bold newspaper headlines followed the fortunes of the U.S. Army, Navy, and Marines on a daily basis. Americans read in detail about the fierce battles in Europe and the Pacific. But the Manhattan Project moved along a completely different track. Groves forbade any publicity about its research and insisted on the compartmentalization of knowledge for all project workers. This meant that a person knew only enough to do his or her task, but no more. This proved frustrating, for ordinary workers as well as for the top-level scientists. Still, a strict culture of secrecy blanketed the entire project.


Meanwhile, the scientists continued their research at a furious pace. Enrico Fermi moved his experiments from Columbia University to the Metallurgical Laboratory (Met Lab) at the University of Chicago, which loaned him a squash court under the unused Stagg football stadium. There Fermi and his crew assembled a gigantic pile of uranium and graphite blocks that reached almost to the ceiling. Fermi had discovered that graphite could be used to moderate, or control, a chain reaction. On the afternoon of December 2, 1942almost four years after Bohr had brought the news of uranium fission to the United StatesFermi oversaw the world`s first controlled release of nuclear energy. The pile produced only enough energy to light a small flashlight, but all the scientists` theories had proven correct: Humankind had created, and, for the moment controlled, the release of atomic energy. All atomic weapons and all nuclear power plants trace their ancestry to this moment.

Fermi`s successful experiment reassured

Fermi`s successful experiment reassured the scientists that they were on the right path, but the technical problems that lay ahead were enormous. General Groves later likened the process to a manufacturer who tried to build an automobile full of watch machinery, with the precision that was required of watchmaking, and the knowledge that the failure of a single part would mean complete failure of the whole project. Perhaps the central hurdle lay with the fact that the most common form of uraniumU238does not fission. The U235 isotope does fission, but only 1 in every 140 uranium atoms is the isotope U235. Thus, the scientists had to devise a means to separate several pounds of U235 from U238 on an atom-by-atom basis. The separation could not be done by chemical methods because the two isotopes are chemically the same. Instead, they had to be separated physically.

Manhattan Project 1 | Manhattan Project 2 | Manhattan Project 3 | Manhattan Project 4 |

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