- For the 1986 movie, see Manhattan Project (film).
The Manhattan Project, or more formally, the Manhattan Engineering District, was an effort during World War II to develop the first nuclear weapon by the United States with assistance from the United Kingdom and Canada. Its research was directed by American physicist J. Robert Oppenheimer, and overall by General Leslie R. Groves after the MAUD Committee had reported that a weapon based on nuclear fission was possible and that Nazi Germany was also investigating such weapons of its own.
The Manhattan Project resulted in the design, production, and detonation of three nuclear bombs in 1945. The first, using plutonium made at Hanford, was tested on July 16 at "Trinity", the world's first nuclear test, near Alamogordo, New Mexico. The second, a uranium bomb called "Little Boy", was detonated on August 6, over the city of Hiroshima, Japan. The third, another plutonium bomb called "Fat Man", was detonated on August 9, over the city of Nagasaki, Japan.
- 1 1900s-1939: Nuclear physics and international politics
- 2 Research in nuclear explosives urged
- 3 Discovery of the feasibility of an atomic bomb
- 4 The program starts in earnest
- 5 The conferences of summer 1942
- 6 Project sites
- 7 Need for coordination
- 8 The Manhattan Engineering District
- 9 The uranium bomb
- 10 The plutonium bomb
- 11 Similar efforts
- 12 See also
- 13 Further reading
- 14 External links
1900s-1939: Nuclear physics and international politics
Because of the discovery of the electron and radioactivity, at the start of the twentieth century the atom was no longer thought to be indivisible. In 1905 Albert Einstein showed in his theory of Special Relativity that a small amount of mass could be converted into a large amount of energy, though the practical significance of this equation was not fully appreciated for many years.
Ernest Rutherford in 1911 then indicated that the majority of an atom's mass was in a small nucleus, made up of protons and this was surrounded by a cloud of electrons. In the 1920s, quantum mechanics provided an explanation for processes in the nucleus such as radioactive decay. In 1932, James Chadwick discovered that the nucleus contained another fundamental particle, the neutron, and in the same year John Cockcroft and Ernest Walton first "split the atom". In 1934, Irène and Frédéric Joliot-Curie discovered that artificial radioactivity could be induced in stable elements by bombarding them with alpha particles, and in the same year Enrico Fermi reported similar results when bombarding uranium with neutrons.
In December 1938, Germans Otto Hahn and Fritz Strassman published experimental results about the bombardment of uranium with neutrons that their collaborator Lise Meitner (a political refugee in Sweden at the time), with Otto Robert Frisch, correctly interpretated for the first time as the splitting of the uranium nucleus after the absorbtion of a neutron — nuclear fission — which released a large amount of energy and additional neutrons. In 1933, Hungarian physicist Leó Szilárd had realized that if a neutron-driven process released more neutrons than required to start, it could result in an expanding nuclear chain reaction — after experimentation, he found that the fission of uranium did indeed release two or more neutrons on average.
That such mechanisms could potentially lead to implications for civilian power or military weapons was perceived by a number of scientists in many different countries around the same time. While all of these developments in science were occuring, however, many great political changes were happening in Europe. Adolf Hitler was appointed chancellor of Germany in January 1933. His anti-Semitic ideology caused all Jewish civil servants, including physicists at universities, to be fired from their posts. Consequently many European physicists who would later make key discoveries went into exile in the United Kingdom and the United States. After Nazi Germany invaded Poland in 1939, World War II began, and many scientists in the United States and Great Britain became anxious about what Germany might do with nuclear technology.
Research in nuclear explosives urged
I remember very vividly the first month, January 1939, that I started working at the Pupin Laboratories because things began happening very fast. In that period, Niels Bohr was on a lecture engagement in Princeton and I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news. The great news that had leaked out was Hahn's and Meitner's discovery of fission and at least the outline of its interpretation. Then, somewhat later that same month, there was a meeting in Washington where the possible importance of the newly discovered phenomenon of fission was first discussed in semi-jocular earnest as a possible source of nuclear power.
Leó Szilárd, Edward Teller and Eugene Wigner (all Hungarian Jewish refugees) believed that the energy released in nuclear fission might be used in bombs by the Germans. They persuaded Albert Einstein, one of the world's most famous physicists and a Jewish refugee himself, to warn President Franklin D. Roosevelt of this danger in an August 2, 1939 letter which Szilárd drafted . In response to the warning, Roosevelt encouraged further research into the national security implications of nuclear fission. After the bombing of Hiroshima, Einstein later commented "I could burn my fingers that wrote that first letter to Roosevelt." The Navy awarded the first atomic energy funding of $6,000 for graphite for experiments.
Roosevelt created an ad hoc Uranium Committee under the chairmanship of National Bureau of Standards chief Lyman Briggs. It began small research programs in 1939 at the Naval Research Laboratory in Washington, where physicist Philip Abelson explored uranium isotope separation. At Columbia University Enrico Fermi, who had emigrated because his wife was Jewish, built prototype nuclear reactors using various configurations of graphite and uranium. The Uranium Committee came under the aegis of the National Defense Research Committee in 1940.
Discovery of the feasibility of an atomic bomb
It had been thought that an atomic bomb would need tons of uranium and so would be difficult to transport. In March 1940 in Birmingham UK, two more German emigrés, Otto Frisch and Rudolf Peierls calculated that an atomic weapon only needed a few pounds of uranium-235 and so it might be practicable. They sent their report, the Frisch-Peierls memorandum, to Henry Tizard, chairman of the Committee for the Scientific Survey of Air Warfare, the most important scientific committee in the British war effort. Tizard set up a sub-committee, the MAUD Committee, to investigate the feasibility in more depth. This committee was under George Paget Thomson, professor of physics at Imperial College, London. After commissioning further research, the MAUD Committee produced their first report in March 1941. The committee confirmed that a uranium bomb could be produced using "about one pound" of the fissionable isotope of uranium, U-235. From this would come an explosion equivalent to that of several thousand tons of TNT. Furthermore their research had shown that isotopic separation of the required quantity of uranium-235 was feasible. Detailed costings followed in another report in July 1941.
Meanwhile in the USA the Uranium Committee had not made comparable progress. The first MAUD Report was sent from Britain to the USA in the March 1941 but no comment was received from the USA.  A member of the MAUD Committee and Frisch's and Peierl's professor, Mark Oliphant, flew to the US in August 1941 in an bomber to find out what was being done with the MAUD reports. He found that Lyman Briggs had simply locked them in his safe, telling nobody, not even the Uranium Committee because the US was "not at war." There was little urgency elsewhere until Oliphant visited Ernest Lawrence, James Conant, chairman of the NDRC, and Enrico Fermi and told them of the MAUD Report. Lawrence also contacted Conant and Arthur Compton, a physicist and Nobel laureate at the University of Chicago, convincing them that they should take Frisch's and Peierl's work very seriously.
The National Academy of Sciences then proposed an all-out effort to build nuclear weapons. On October 9, 1941 Roosevelt authorized atomic weapon development. Bush created a special committee, the S-1 Committee, to guide the effort. This happened to be on the day before the Japanese attack on Pearl Harbor, which was on December 7th, 1941, and meant the start of the war for the United States. In 1941 NDRC was subsumed into the Office of Scientific Research and Development to expand these efforts.
The program starts in earnest
In December 1941, scientists at the University of Chicago Metallurgical Laboratory, the University of California Radiation Laboratory and Columbia University's physics department, accelerated their efforts to prepare the nuclear materials for a weapon.
Arthur Compton organized the Metallurgical Laboratory at the University of Chicago in early 1942 to study plutonium and fission piles. Compton asked theoretical physicist Dr. J. Robert Oppenheimer of the University of California to take over research on fast neutron calculations, essential to the development of a nuclear weapon. John Manley, a physicist at the University of Chicago Metallurgical Laboratory, was assigned to help Dr. Oppenheimer find answers by coordinating and contacting several experimental physics groups scattered across the country.
Plutonium seemed to provide a better method of making a bomb, but much less was known about it. Two parallel and completely separate efforts were undertaken. One project produced a uranium bomb and the other route produced two plutonium bombs, all of which were successfully detonated in 1945.
The conferences of summer 1942
In the spring of 1942, Oppenheimer and Robert Serber of the University of Illinois, worked on the problems of neutron diffusion (how neutrons moved in the chain reaction) and hydrodynamics (how the explosion produced by the chain reaction might behave). To review this work and the general theory of fission reactions, Oppenheimer convened a summer study at the University of California, Berkeley in June 1942. Theorists Hans Bethe, John Van Vleck, Edward Teller, Felix Bloch, Emil Konopinski, Robert Serber, Stanley S. Frankel, and Eldred C. Nelson (the latter three all former students of Oppenheimer) confirmed that a fission bomb was feasible. The scientists suggested that such a reaction could be initiated by assembling a critical mass - an amount of nuclear explosive adequate to sustain it - either by firing two subcritical masses of plutonium or uranium 235 together or by imploding (crushing) a hollow sphere made of these materials with a blanket of high explosives. (Serber credits an early idea of implosion to Tolman). Until more quantitative data on fission reactions became available, this was all that could be done.
Teller saw another possibility: by surrounding a fission bomb with deuterium and tritium, a much more powerful "superbomb" (which he called simply, the "Super") might be constructed. This concept was based on studies of energy production in stars made by Bethe before the war. When the detonation wave from the fission bomb moved through the mixture of deuterium and tritium nuclei, these would fuse together to produce much more energy than fission could. This process of nuclear fusion is similar to the way that elements fuse in stars to produce light.
Bethe was skeptical. As Teller pushed hard for his "superbomb", proposing scheme after scheme, Bethe refuted each one. The fusion idea had to be put aside while the fission bombs, and the war, were completed. (The "super", or thermonuclear device, was produced after the war and tested in 1952, after an acrimonious political fight pitting Teller against Oppenheimer, leading to loss of Oppenheimer's official status. However the H-bomb used methods different than Teller's, which Bethe had correctly refuted.)
Teller also raised the speculative possibility that an atomic bomb might "ignite" the atmosphere, due to a hypothetical fusion reaction of nitrogen nuclei. Bethe calulated, according to Serber, that it could not happen. In his book The Road from Los Alamos, Bethe says a refutation was written by Konopinski, C. Marvin, and Teller as report LA-602 (declassified Feb. 1973 online), showing that ignition of the atmosphere was impossible, not just unlikely. In Serber's account, Oppenheimer unfortunately mentioned it to Arthur Compton, who "didn't have enough sense to shut up about it. It somehow got into a document that went to Washington" which led to the question "never [being] laid to rest". In Bethe's account, this ultimate catastrophe came up again in 1975 when it appeared in a magazine article by H. C. Dudley, who got the idea from a report by Pearl Buck of an interview she had with Arthur Compton in 1959, where she completely misunderstood Compton! The worry was not entirely extinguished in some people's minds until the Trinity test; though if Bethe had been wrong, we would never know.
The conferences in the summer on 1942 provided the detailed theoretical basis for the design of the atomic bomb at Los Alamos. The conclusions were later summarized by Serber in "The Los Alamos Primer" (LA-1 online).
Though it involved over thirty different research and production sites, the Manhattan Project was largely carried out in three secret scientific cities that were established by power of eminent domain: Hanford, Washington, Los Alamos, New Mexico, and Oak Ridge, Tennessee. The Los Alamos National Laboratory was built on a mesa that previously hosted the Los Alamos Ranch School. The Hanford Site, which grew to almost 1000 square miles (2,600 km²), took over irrigated farm land, fruit orchards, a railroad, and two active farming communities, Hanford and White Bluffs. The Oak Ridge facilities cover more than 60,000 acres (243 km²) of several former farm communities. Some Tennessee families were given two weeks notice to vacate family farm lands that had been their home for generations. The existence of these sites and the secret cities of Los Alamos, Oak Ridge, and Hanford was officially secret until the end of WWII.
Need for coordination
The measurements of the interactions of fast neutrons with the materials in a bomb were essential because the number of neutrons produced in the fission of uranium and plutonium must be known, and because the substance surrounding the nuclear material must have the ability to reflect, or scatter, neutrons back into the chain reaction before it is blown apart in order to increase the energy produced. Therefore, the neutron scattering properties of materials had to be measured to find the best reflectors.
Estimating the explosive power required knowledge of many other nuclear properties, including the cross section (a measure of the probability of an encounter between particles that result in a specified effect) for nuclear processes of neutrons in uranium and other elements. Fast neutrons could only be produced in particle accelerators, which were still relatively uncommon instruments in physics departments in 1942.
The need for better coordination was clear. By September 1942, the difficulties involved with conducting preliminary studies on nuclear weapons at universities scattered throughout the country indicated the need for a laboratory dedicated solely to that purpose. An even greater need was the construction of massive industrial plants to produce uranium-235 and plutonium - the fissionable materials that would provide the nuclear explosives.
Vannevar Bush, the head of the civilian Office of Scientific Research and Development (OSRD), asked President Roosevelt to assign the large-scale operations connected with the quickly growing nuclear weapons project to the military. Roosevelt chose the Army to work with the OSRD in building production plants. The Army Corps of Engineers selected Col. James Marshall to oversee the construction of factories to separate uranium isotopes and manufacture plutonium for the bomb.
Marshall and his deputy, Col. Kenneth Nichols, had to struggle to understand the various proposed processes and the scientists with whom they had to work. Thrust suddenly into the new field of nuclear physics, they felt unable to distinguish between technical and personal preferences. Although they decided that a site near Knoxville would be suitable for the first production plant, they did not know how large the site had to be and so put off its acquisition. There were other problems, too.
Because of its experimental nature, the nuclear weapons work could not compete with the Army's more-urgent tasks for top-priority ratings. The selection of scientists' work and production-plant construction often were delayed by Marshall's inability to get the critical materials, such as steel, that also were needed in other military productions.
Even selecting a name for the new Army project was difficult. The title chosen by Gen. Brehon Somervell, "Development of Substitute Materials," was objectionable because it seemed to reveal too much.
The Manhattan Engineering District
In the summer of 1942, Col. Leslie Groves was deputy to the chief of construction for the Army Corps of Engineers and had overseen construction of the Pentagon, the world's largest office building. Hoping for an overseas command, Groves vigorously objected when Somervell appointed him to take charge of the weapons project. His objections were overruled and Groves resigned himself to leading a project he thought had little chance of succeeding. Groves appointed Oppenheimer as the project's scientific director, to the surprise of many. (Oppenheimer's radical political views were thought to pose security problems).
The first thing he did was rechristen the project The Manhattan District. The name evolved from the Corps of Engineers practice of naming districts after its headquarters' city (Marshall's headquarters were in New York City). At the same time, Groves was promoted to brigadier general, which gave him the rank thought necessary to deal with the senior scientists in the project.
Within a week of his appointment, Groves had solved the Manhattan Project's most urgent problems. His forceful and effective manner was soon to become all too familiar to the atomic scientists.
The first major scientific hurdle of the project was solved on December 2, 1942 beneath the bleachers of Stagg Field at the University of Chicago, where a team led by Enrico Fermi initiated the first self-sustaining nuclear chain reaction in an experimental reactor named Chicago Pile-1. A coded phone call from Compton saying, "The Italian navigator (referring to Fermi) has landed in the new world, the natives are friendly" to Conant in Washington, DC, brought the news that the experiment was a success. This was a major turning point.
The uranium bomb
The Hiroshima bomb, Little Boy, was made from uranium-235, a rare isotope of uranium that has to be physically separated from more prevalent uranium-238 isotope, which is not suitable for use in an explosive device. However U-235 is only 0.7% of raw uranium and chemically identical to the 99.3% of U-238, so various physical methods were considered for separation.
One method of separating uranium 235 from raw uranium ore was devised by Franz Simon and Nicholas Kurti, two more Jewish emigrés, at Oxford University. Their method using gaseous diffusion was scaled up in large separation plants at Oak Ridge Laboratories. These used uranium hexafluoride (UF6) gas as the process fluid, see gaseous diffusion. This method eventually produced most of the U-235.
Another method - electromagnetic isotope separation, which had been developed by Ernest Lawrence at the University of California Radiation Laboratory at the University of California, Berkeley - seemed promising for a while large-scale production, but it proved to be expensive and unlikely that it alone could produce enough material before the war was over. Other techniques were also tried, such as thermal diffusion, and the calutron method, using the mass spectrometer principle of magnetic separation. Most of this separation work was performed at Oak Ridge.
The uranium bomb used the so-called "gun" mechanism to assemble a critical mass of the U-235; one mass of U-235, the "bullet," was fired down a tube into another mass of U-235, suddenly creating a critical mass of U-235 which resulted in a huge explosion.
The plutonium bomb
In contrast, the bombs used in the first test at Trinity Site, New Mexico (the gadget of the Trinity test), and also in the Nagasaki bomb, Fat Man, were made primarily of Plutonium-239. Plutonium is a synthetic element.
Although uranium-238 is useless as fissile material for an atomic bomb, U-238 is used to produce plutonium. The fission of U-235 produces relatively slow neutrons which will be absorbed by U-238, which after a few days of decay, turns into plutonium-239. The production and purification of plutonium used techniques developed in part by Glenn Seaborg while working at Berkeley and Chicago. Beginning in 1943, huge plants were built to produce plutonium at Hanford (Site W) outside of Richland, Washington.
Initial tests of the properties of plutonium were done using cyclotron-generated plutonium-239, which was very pure but in very small amounts. On April 5, 1944, Emilio Segrè at Los Alamos received the first sample of Hanford-produced plutonium. Within ten days, he discovered a fatal flaw: reactor-bred plutonium was far less pure than cyclotron-produced plutonium, and as a result had a much higher spontaneous fission rate than uranium-235. The implications of this made a "gun" detonation mechanism unsuitable: because of the relatively slow speed of the gun mechanism, a plutonium bomb would "fizzle" (i.e. blow itself apart before it developed a substantial chain reaction).
Ideas of using alternative detonation schemes had existed for some time at Los Alamos. One of the more innovative had been the idea of "implosion" — a sub-critical sphere of fissile material could, using chemical explosives, be forced to collapse in on itself, creating a very dense critical mass. Initially it had been entertained as a possible, though unlikely possibility. But after it was discovered that it was the only possible solution for using plutonium in a nuclear weapon, it received the highest project priority. By the end of July 1944, the entire project had been re-organized around solving the implosion problem. It eventually involved using shaped charges with many explosive lenses in order to produce the perfectly-spherical explosive wave needed for proper compression of the plutonium sphere.
Because of the complexity of detonating an implosion-style weapon necessary for the plutonium bomb, it was decided that a test would be required in order to have any confidence that it would work in practice (and not just be a waste of expensive fissile material). After much preparation, the first nuclear test took place on July 16, 1945, near Alamagordo, New Mexico, and was dubbed by Oppenheimer as "Trinity".
A similar effort was undertaken in the USSR headed by Igor Kurchatov (with a specific difference in that some of Kurchatov's World War II investigations came secondhand from Manhattan Project countries, thanks to spies, including at least two on the scientific team at Los Alamos, Klaus Fuchs and Theodore Hall, unknown to each other).
After the MAUD Committee's report, the British and Americans exchanged nuclear information, but initally did not pool their efforts. A separate British project, code-named TUBE ALLOYS, was started but did not have American resources. Consequently the British bargaining position worsened and their motives were mistrusted by the Americans. Collaboration therefore lessened markedly until the Quebec Agreement of August 1943, when a large team of British scientists joined the Manhattan Project.
Axis efforts on the bomb has always been an issue of contention, while it is believed that token efforts in Germany, (headed by Werner Heisenberg,) and in Japan, were also undertaken during the war but made little progress. It was initially feared that Hitler was very close to developing his own bomb. Many Nazi scientists had in fact expressed suprise to their allied captors when the bombs were detonated in Japan; convinced that it was merely propaganda. Incidently Niels Bohr and Heisenberg discussed the possibility of the atomic bomb prior to and during the war. Bohr had recalled that Heisenberg was unaware that the supercritical mass could be achieved with U-235. In fact, Bohr, Heisenberg and Fermi were all collegues who were key figures in developing the quantum theory together with Wolfgang Pauli prior to the war.
Together with the cryptographic efforts centered at Bletchley Park and also at Arlington Hall, the development of radar and computers in the UK and later in the USA, and the jet engine in the UK and Germany, the Manhattan Project represents one of few massive, secret, and outstandingly successful technological efforts spawned by the conflict of World War II.
- Timeline of the Manhattan Project
- August 1945
- Related locations
- Hanford Site (plutonium production)
- Ames Laboratory (uranium production from ores)
- Los Alamos National Laboratory (secret weapons lab)
- Lawrence Livermore National Laboratory (second weapons lab, created in 1950s)
- Metallurgical Laboratory (first controlled nuclear chain reaction)
- Oak Ridge National Laboratory (uranium enrichment)
- Trinity site (first nuclear test)
- Nuclear weapons
- Other projects
- Badash, Lawrence, Joseph O. Hirschfelder, Herbert P. Broida, (eds) Reminiscences of Los Alamos, 1943-1945, Dordrecht, Boston: D. Reidel, 1980, ISBN 902771097X, LoC QC791.96.R44
- Bethe, Hans A. The Road from Los Alamos, NY: Simon and Schuster, 1991, ISBN 0671740121
- Groueff, Stephane, Manhattan Project: The Untold Story of the Making of the Atomic Bomb, (Boston: Little, Brown & Co, 1967) The definitive history of the technical work of the Project, including many of its little-known technical achievements.
- Jungk, Robert, Brighter Than a Thousand Suns: A Personal History of the Atomic Scientists, (NY: Harcourt, Brace, 1956, 1958)
- Groves, Leslie, Now it Can be Told: The Story of the Manhattan Project (New York: Harper, 1962) The managerial history of the Project, by its leader.
- Herken, Gregg, Brotherhood of the Bomb : The Tangled Lives and Loyalties of Robert Oppenheimer, Ernest Lawrence, and Edward Teller (New York: Henry Holt and Co., 2002). ISBN 0805065881
- Hoddeson, Lillian, Paul W. Henriksen, Roger A. Meade, and Catherine L. Westfall, Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943-1945, Cambridge, 1993
- Nichols, Kenneth David, The Road to Trinity: A Personal Account of How America's Nuclear Policies Were Made (New York: William Morrow and Company Inc, 1987). ISBN 068806910X
- Rhodes, Richard, The Making of the Atomic Bomb (New York: Simon & Schuster, 1986) ISBN 0671441337 An excellent contemporary overall history of the Project.
- Serber, Robert, The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb (University of California Press, 1992) ISBN 0520075765 Original 1943, "LA-1", declassified in 1965. (Available on Wikimedia Commons).
- Serber, Robert, Peace and War: Reminiscences of a Life on the Frontiers of Science, (NY: Columbia Un. Press, 1998), ISBN 0231105460, LoC QC16.S46A3 1998
- Sherwin, Martin J., A World Destroyed: The Atomic Bomb and the Grand Alliance (New York: Alfred A. Knopf, 1975). ISBN 0394497945
- Smyth, Henry DeWolf, Atomic Energy for Military Purposes; the Official Report on the Development of the Atomic Bomb under the Auspices of the United States Government, 1940-1945 (Princeton: Princeton University Press, 1945). (Smyth Report)
- US House of Representatives, 81st Congress, 2nd Session, Committee on Un-American Activities, Hearings Regarding Shipment of Atomic Material to the Soviet Union During World War II (DC, US Gov Printing Office [GPO], 1950
- National Atomic Museum | The Manhattan Project
- Children of the Manhattan Project
- B Reactor Museum Association A collection of Hanford-related documents from a group fighting to preserve the B-100 Reactor at Hanford.
- Eye witness accounts of the Trinity test. If you want to read some extreme writing, read this.
- Press release from Truman annoucing the bombing of Hiroshima August 6, 1945.
- Development of the Atomic Bomb
- Federation of American Scientists Many Los Alamos reports were put on web in 2000, then later removed. Currently stored at fas.org
- Truth of Atomic Bomb : from Hiroshima
- Origins of the project
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