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The Manhattan Project was the codename for a project conducted during World War II.The project was led by the United Statesmarker, and included participation from the United Kingdommarker and Canadamarker. Formally designated as the Manhattan Engineer District (MED), it refers specifically to the period of the project from 1942–1946 under the control of the U.S. Army Corps of Engineers, under the administration of General Leslie R. Groves. The scientific research was directed by American physicist J. Robert Oppenheimer.

The project's roots lay in scientists' fears since the 1930s that Nazi Germany was also investigating nuclear weapons of its own. Born out of a small research program in 1939, the Manhattan Project eventually employed more than 130,000 people and cost nearly US$2 billion ($ billion in current value). It resulted in the creation of multiple production and research sites that operated in secret.

Project research took place at over thirty sites across the United States, Canada, and the United Kingdom. The three primary research and production sites of the project were the plutonium-production facility at what is now the Hanford Sitemarker, the uranium-enrichment facilities at Oak Ridge, Tennesseemarker, and the weapons research and design laboratory now known as Los Alamos National Laboratorymarker. The MED maintained control over U.S. weapons production until the formation of the Atomic Energy Commission in January 1947.

Discovery of nuclear fission

The first decades of the 20th century led to radical changes in the understanding of the physics of the atom, including the discovery of the nucleus, the idea of radiation, and the fact that the splitting of atomic nuclei in a chain reaction could lead to massive release of energy (nuclear fission).

By 1933 the atom was thought to consist of a small, dense nucleus containing most of the atom's mass in the form of protons and neutrons and surrounded by a shell of electrons. Study on the phenomenon of radioactivity began in 1896 with the discovery of uranium ores by Henri Becquerel and was followed by the work of Pierre and Marie Curie on radium. Their research seemed to promise that atoms, previously thought to be ultimately stable and indivisible, actually had the potential of containing and releasing immense amounts of energy. In 1919 Ernest Rutherford achieved the first artificial nuclear disintegrations by bombarding nitrogen with alpha particles emitted from a radioactive source, thus becoming the first person in history to intentionally "split the atom". It became clear from the Curies' work that there was a tremendous amount of energy locked up in radioactive decay—far more than chemistry could account for. The source of this energy, as given by Albert Einstein's famous E = mc2 formula, was that some of the mass in the nucleus was being converted to energy, and that a very small amount of mass could produce an enormous amount of energy. But even in the early 1930s such illustrious physicists as Einstein and Ernest Rutherford could see no way of artificially releasing that energy any faster than nature naturally allowed it to leave. "Radium engines" in the 1930s were the stuff of science fiction, such as was being written at the time by Edgar Rice Burroughs. H.G. Wells included air-dropped "atomic bombs" in his 1914 novel The World Set Free. Though Wells' "atomic bombs" bore little resemblance to actual nuclear weapons—they were simply regular bombs that never stopped exploding—Leó Szilárd later commented that this story influenced his later research into this subject.

Progress in controlling and understanding nuclear fission accelerated in the 1930s when further manipulation of the nuclei of atoms became possible. In 1932 Sir John Cockcroft and Ernest Walton were first to "split the atom" (cause a nuclear reaction) by using artificially accelerated particles. In 1934 Irène and Frédéric Joliot-Curie discovered that artificial radioactivity could be induced in stable elements by bombarding them with alpha particles. The same year Enrico Fermi reported similar results when bombarding uranium with neutrons (discovered in 1932), but he did not immediately appreciate the consequences of his results.

In December 1938 Germansmarker Otto Hahn and Fritz Strassmann published experimental results about bombarding uranium with neutrons. They showed that it produced an isotope of barium. Shortly after, their Austrian co-worker Lise Meitner (a political refugee in Sweden at the time) and her nephew Otto Robert Frisch correctly interpreted the results as the splitting of the uranium nucleus after the absorption of a neutron—nuclear fission, which released a large amount of energy and additional neutrons. A direct experimental evidence of the nuclear fission was performed by Frisch, following a fundamental idea suggested to him by George Placzek.

That such mechanisms might have implications for civilian power or military weapons was perceived by numerous scientists in many countries, around the same time. While these developments in science were occurring, many political changes were happening in Europe. Adolf Hitler was appointed chancellor of Germany in January 1933. Within three months of taking power, the Nazis passed the Law for the Restoration of the Professional Civil Service, which caused all Jewish civil servants, including many physicists, to be fired from their posts. Consequently many European physicists who later made key discoveries went into exile in the United Kingdom and the United States. After Nazi Germany invaded Poland in 1939 and World War II began, many scientists in the United States and the United Kingdom became anxious about what Germany might do with nuclear technology. Albert Einstein in particular wrote several letters to Franklin Roosevelt urging him to establish nuclear capability before the Germans. These letters, especially one called the Einstein–Szilárd letter (dated August 2, 1939, but not personally received by Roosevelt until October 1939), brought American government attention and support to nuclear research.


It is widely believed that the Manhattan Project's name is simply a code name. In fact, the project was named after the location where many of its early operations were conducted - Manhattan. According to historian Robert Norris, Manhattan contained at least ten sites where the project's work was being conducted—the island was ideal because of its port facilities, the military presence, a large available work force, a population of expatriate European physicists, and Columbia University, a center of early nuclear research.

Uranium Committee (1939–1941)

In 1939, President Franklin Roosevelt called on Lyman Briggs of the National Bureau of Standards to head "The Uranium Committee" as a result of the Einstein–Szilárd letter. Even though Roosevelt had sanctioned the project, progress was slow and was not directed exclusively towards military applications.

Meanwhile, in the United Kingdommarker, Otto Frisch and Rudolf Peierls made a breakthrough by discovering the fissile properties of uranium-235. A British committee, the MAUD Committee, concluded that:
(i) The committee considers that the scheme for a uranium bomb is practicable and likely to lead to decisive results in the war

(ii) It recommends that this work continue on the highest priority and on the increasing scale necessary to obtain the weapon in the shortest possible time

(iii) That the present collaboration with America should be continued and extended especially in the region of experimental work

Their reports were sent to Briggs, but were ignored. One of the members of the MAUD Committee, Mark Oliphant, flew to the United States in late August 1941 to find out why the U.S. was ignoring the MAUD Committee's findings. He reported that "this inarticulate and unimpressive man (Briggs) had put the reports in his safe and had not shown them to members of his committee."

Oliphant then met with the whole Uranium Committee and other physicists to galvanize the USA into action. As a result, in December 1941 Vannevar Bush created the larger and more powerful Office of Scientific Research and Development—which was empowered to engage in large engineering projects in addition to research—and became its director.

Acceleration of the Project

Now that the bomb project was under the OSRD, the project leaders began to accelerate the work. Arthur Compton organized the University of Chicago Metallurgical Laboratory in early 1942 to study plutonium and fission piles (primitive nuclear reactors), and asked theoretical physicist J. Robert Oppenheimer of the University of California, Berkeleymarker to take over research on fast neutron calculations—key to calculations about critical mass and weapon detonation—from Gregory Breit, who had quit because of concerns over lax operational security. John Manley, a physicist at the Metallurgical Laboratory, was assigned to help Oppenheimer find answers by coordinating and contacting several experimental physics groups scattered across the country.

During the spring of 1942 , Oppenheimer and Robert Serber of the University of Illinoismarker 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) quickly confirmed that a fission bomb was feasible.

There were still many unknown factors in the development of a nuclear bomb, however, even though it was considered to be theoretically possible. The properties of pure uranium-235 were still relatively unknown, as were the properties of plutonium, a new element which had only been discovered in February 1941 by Glenn Seaborg and his team. Plutonium was the product of uranium-238 absorbing a neutron which had been emitted from a fissioning uranium-235 atom, and was thus able to be created in a nuclear reactor. But at this point no reactor had yet been built, so while plutonium was being pursued as an additional fissile substance, it was not yet to be relied upon. Only microgram quantities of plutonium existed at the time (produced from neutrons derived from reaction started in a cyclotron).

The scientists at the Berkeley conference determined that there were many possible ways of arranging the fissile material into a critical mass, the simplest being the shooting of a "cylindrical plug" into a sphere of "active material" with a "tamper"—dense material which would focus neutrons inward and keep the reacting mass together to increase its efficiency (this model "avoids fancy shapes", Serber would later write). They also explored designs involving spheroids, a primitive form of "implosion" (suggested by Richard C. Tolman), and explored the speculative possibility of "autocatalytic methods" which would increase the efficiency of the bomb as it exploded.

Considering the idea of the fission bomb theoretically settled—at least until more experimental data was available—the conference then turned in a different direction. Hungarian physicist Edward "Ede" Teller pushed for discussion on an even more powerful bomb: the "Super", which would use the explosive force of a detonating fission bomb to ignite a fusion reaction in deuterium and tritium. Such a bomb, they calculcated, would have an explosive yield of 10 megatons, hundreds of times more powerful than the atomic bomb. The concept was based on studies of energy production in stars made by Hans Bethe before the war, and suggested as a possibility to Teller by Enrico Fermi not long before the conference. 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. But Bethe was skeptical. As Teller pushed hard for his "superbomb"—now usually referred to as a "hydrogen bomb"—proposing scheme after scheme, Bethe refused each one. The fusion idea had to be put aside in order to concentrate on actually producing fission bombs.

Teller also raised the speculative possibility that an atomic bomb might "ignite" the atmosphere because of a hypothetical fusion reaction of nitrogen nuclei. Bethe calculated, according to Serber, that it could not happen. However, a report co-authored by Teller showed that ignition of the atmosphere was not impossible, just unlikely. In Serber's account, Oppenheimer 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 being "never laid to rest".

The conferences in June 1942 provided the detailed theoretical basis for the design of the atomic bomb, and convinced Oppenheimer of the benefits of having a single centralized laboratory to manage the research for the bomb project rather than having specialists spread out at different sites across the United States.

Project sites

Though it involved over thirty different research and production sites, the Manhattan Project was largely carried out at four secret laboratories that were established by power of eminent domain in four cities: Los Alamos, New Mexicomarker; Oak Ridge, Tennesseemarker; Richland, Washingtonmarker; Chalk River, Ontario, Canadamarker. The Tennessee site was chosen because of the vast quantities of cheap hydroelectric power already available there (from the Tennessee Valley Authority) to power uranium enrichment processes. The Hanford Sitemarker near Richland, Washington, was chosen for its location near the Columbia River, a river that could supply water to cool the reactors which would produce the plutonium. The Canadian site, Chalk River, Ontario, was chosen for its proximity to the industrial manufacturing of Ontario and Quebec, located on a rail head, adjacent to a large military base, Camp Petawawa, located on the Ottawa River it had access to abundant water. All the sites were suitably far from coastlines and therefore less vulnerable to possible enemy attack from Germany or Japan.

The Los Alamos National Laboratorymarker was built on a mesa that previously hosted the Los Alamos Ranch School, a private school for teenage boys. The site was chosen primarily for its remoteness. Oppenheimer had known of it from his horse-riding near his ranch in New Mexico, and he showed it as a possible site to the government representatives, who promptly bought it for $440,000. In addition to being the main "think-tank", Los Alamos was responsible for final assembly of the bombs, mainly from materials and components produced by other sites. Manufacturing at Los Alamos included casings, explosive lenses, and fabrication of fissile materials into bomb cores.

Oak Ridge facilities covered more than 60,000 acres (243 km²) of several former farm communities in the Tennessee Valley area. Some Tennessee families were given two weeks' notice to vacate family farms that had been their homes for generations. So secret was the site during World War II that the state governor was unaware that Oak Ridge (which was to become the fifth largest city in the state) was being built. At one point Oak Ridge plants were consuming 1/6th of the electrical power produced in the U.S., more than New York City. Oak Ridge mainly produced uranium-235.

Chalk River, was established to house the allied effort that was going on at McGill University, in Montreal. Since the site was 120 miles west of Ottawa, a new community was also built at Deep River, Ontario to be the home of the project team members. Both were established in 1944, with scientists, engineers, trades from Canada, the United Kingdom, New Zealand, Australia, France, Norway, etc. providing their contribution to the war effort.

The Hanford Site, which grew to almost 1,000 square miles (2,600 km²), took over irrigated farm land, fruit orchards, a railroad, and two farming communities, Hanfordmarker and White Bluffsmarker, in a highly populated area where three cities converge called the Tri Cities, (Kennewick, Pasco, and Richland. WA),adjacent to the Columbia River. Hanford hosted nuclear reactors cooled by the river and was the plutonium production center.

The existence of these sites and the secret cities of Los Alamos, Oak Ridge, Richland, and Chalk River were not made public until the announcement of the Hiroshima explosion, and the sites remained secret until after the end of WWII.

The project originally was headquartered at 270 Broadwaymarker in Manhattanmarker. Other offices were scattered throughout the city, including the New York Friars' Clubmarker building. The Broadway headquarters lasted little more than a year before it was moved in 1943, although many of the other offices in Manhattan remained.
A selection of U.S. sites important to the Manhattan Project.

Major Manhattan Project sites and subdivisions included:

Need for coordination

The measurements of the interactions of fast neutrons with the materials in a bomb were essential; because the scientists needed to know the number of neutrons produced in the fission of uranium and plutonium, and because the substance surrounding the nuclear material needed the ability to reflect, or scatter, neutrons back into the chain reaction before it was blown apart—this 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 1942.

The need for better coordination was clear. By September 1942, the difficulties in conducting studies on nuclear weapons at universities scattered throughout the country indicated the need for a laboratory dedicated solely to that purpose. A greater need was the construction of industrial plants to produce uranium-235 and plutonium—the fissionable materials to be used in the weapons.

Vannevar Bush, the head of the civilian Office of Scientific Research and Development (OSRD), asked President Roosevelt to assign the operations connected with the 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, struggled to understand the proposed processes and the scientists with whom they had to work. Thrust 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, Tennesseemarker, would be suitable for the first production plant, they did not know how large the site needed to be, and thus delayed its acquisition.

Because of its experimental nature, the nuclear weapons work could not compete for priority with the Army's more urgent tasks. The scientists' construction of the work and production plants were often delayed by Marshall's inability to obtain critical materials—such as steel—needed in other military projects.

Even selecting a name for the project was difficult. The title chosen by Gen. Brehon B. Somervell, "Development of Substitute Materials," was objectionable because it seemed to reveal too much.

Manhattan Engineer District

Vannevar Bush became dissatisfied with Col. James Marshall's failure to get the project moving forward expeditiously and made this known to Secretary of War Stimson and Army Chief of Staff George Marshall. Marshall then directed General Somervell to replace Col. Marshall with a more energetic officer as director. In the summer of 1942 , Col. Leslie Groves was deputy to the chief of construction for the Army Corps of Engineers and had overseen the very rapid construction of the Pentagonmarker, the world's largest office building. He was widely respected as an intelligent, hard driving, though brusque officer who got things done in a hurry. Hoping for an overseas command, Groves vigorously objected when Somervell appointed him to the weapons project. His objections were overruled, and Groves resigned himself to leading a project he thought had little chance of success. 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). However, Groves was convinced Oppenheimer was a genius who could talk about and understand nearly anything, and he was convinced such a man was needed for a project such as the one being proposed.

Groves renamed the project The Manhattan Engineer District. The name evolved from the Corps of Engineers practice of naming districts after its headquarters' city (Marshall's headquarters were at 270 Broadwaymarker in New York City). At that time, Groves was promoted to brigadier general, giving him the rank necessary to deal with senior people whose cooperation was required, or whose own projects were hampered by Groves' top-priority 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 Fieldmarker at the University of Chicago, where a team led by Enrico Fermi, for whom Fermilabmarker is named, initiated the first artificial self sustaining nuclear chain reaction in an experimental nuclear reactor named Chicago Pile-1marker. 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, D.C.marker, brought news of the experiment's success.

Uranium bomb

A gun-type nuclear bomb.
The Hiroshima bomb, Little Boymarker, was made from uranium-235, a rare isotope of uranium that has to be physically separated from the more plentiful uranium-238 isotope, which is not suitable for use in an explosive device. Since U-235 makes up only 0.7% of raw uranium and is chemically identical to the 99.3% of U-238, various physical methods were considered for separation. Most of the uranium enrichment work was performed at Oak Ridge.

One method of separating uranium 235 from raw uranium ore was devised by Franz Simon and Nicholas Kurti, at Oxford Universitymarker. Their method using gaseous diffusion was scaled up in a large separation plantmarker at Oak Ridge, using uranium hexafluoride (UF6) gas as the process fluid. During the war this method was important primarily for producing partly enriched material to feed the electromagnetic separation process undertaken in calutrons (see below).

Another method—electromagnetic isotope separation—was developed by Ernest Lawrence at the University of California Radiation Laboratory at the University of California, Berkeleymarker. This method was implemented in Oak Ridge at the Y-12 Plantmarker, employing devices known as calutrons, which were effectively mass spectrometers. Copper was originally intended for electromagnet coils, but there was an insufficient amount available due to war shortages. The project engineers were forced to borrow silver from the U.S.marker Treasurymarker. A total of 70,000,000 pounds of silver from the U.S. Treasury reserves was used for coils, and was returned after the project ended. Initially the method seemed promising for large scale production but was expensive and produced insufficient material and was later abandoned after the war.

Other techniques were also tried, such as thermal diffusion and the use of high-speed centrifuges. Thermal diffusion was not used to produce highly-enriched uranium, but was used during the war in the S-50 facility to begin enrichment of the uranium, and its product was passed as the feed into the other facilities.

The uranium bomb was a gun-type fission weapon. One mass of U-235, the "bullet," is fired down a more or less conventional gun barrel into another mass of U-235, rapidly creating the critical mass of U-235, resulting in an explosion. The method was so certain to work that no test was carried out before the bomb was dropped over Hiroshima, though extensive laboratory testing was undertaken to make sure the fundamental assumptions were correct. Also, the bomb that was dropped used all the existing extremely highly purified U-235 (and even most of the less highly purified material) so there was no U-235 available for such a test anyway. The bomb's design was known to be inefficient and prone to accidental discharge.

Plutonium bomb

The basic concept of an implosion-style nuclear weapon.
Actual pictures and details of the bomb's inner workings remain classified.

The bombs used in the first test at Trinity Sitemarker on July 16, 1945, in New Mexico (the gadget of the Trinity testmarker), and in the Nagasaki bomb, Fat Manmarker, were made primarily of plutonium-239, a synthetic element.

Although uranium-238 is useless as a fissile isotope for an atomic bomb, it is key in producing plutonium . The fission of U-235 releases neutrons, which are absorbed by U-238, which creates uranium-239. U-239 rapidly decays to neptunium-239 (U-239 has a half-life of 23.45 minutes). Neptunium-239 (with a half-life of 2.35 days) then decays 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 the Hanford Sitemarker.
A mock-up of the plutonium bomb, Fat Man
In 1943–1944, development efforts were directed to a gun-type fission weapon with plutonium, called "Thin Man". Once this was achieved, the scientists thought the uranium version, "Little Boy," would require a relatively simple adaptation.

Initial research on the properties of plutonium was done using cyclotron-generated plutonium-239, which was extremely pure, but could only be created 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 problem: reactor-bred plutonium was far less isotopically pure than cyclotron-produced plutonium. A higher concentration of Pu-240, formed from Pu-239 by capture of an additional neutron, gave it a much higher spontaneous fission rate than U-235. Pu-240 was even harder to separate from Pu-239 than U-235 was to separate from U-238, so no purification was attempted. This made the Hanford plutonium unsuitable for use in a gun-type weapon .

The gun-type bomb worked by mechanically assembling the critical mass from two subcritical masses: a "bullet" and a target. The chain reaction resulting from collision of the "bullet" with the target released tremendous energy, producing an explosion, but also blew apart the critical mass and ended the chain reaction. The configuration of the critical mass determined how much of the fissile material reacted in the interval between assembly and dispersal, and therefore the explosive yield of the bomb. Even a 1% fission of the material would result in a workable bomb, equal to thousands of tons of high explosive. A poor configuration, or slow assembly, would release enough energy to disperse the critical mass quickly, and the yield would be greatly reduced, equivalent to only a few tons of high explosive.

The chain reaction of U-235 was slow enough that gun-type assembly would work, but in a gun-type bomb made with the Hanford plutonium, "early" neutrons from spontaneously fissioning Pu-240 would start the chain reaction more quickly during detonation. This would release enough energy to disperse the critical mass with only a minimal amount of plutonium reacted, reducing the resulting yield of the weapon.

In July 1944, based on the measurements of spontaneous fission for Hanford plutonium, the decision was made to cease work on a gun-type assembly for plutonium. There would be no "Thin Man."

Ideas for alternative detonation schemes had existed for some time at Los Alamos. One of the more innovative was the idea of "implosion". Using chemical explosives, a sub-critical sphere of fissile material could be squeezed into a smaller and denser form. When the fissile atoms were packed closer together, the rate of neutron capture would increase, and the mass would become a critical mass. The metal needed to travel only very short distances, so the critical mass would be assembled in much less time than it would take to assemble a mass by a bullet impacting a target.Initially, implosion had been entertained as a possible, though unlikely, method.

The gun method was further developed for uranium only, while most efforts were then directed towards rapidly developing an implosion system. Oppenheimer chose to pursue a design based on the April 1944 suggestion by James L. Tuck to use explosive lenses to create spherical, converging implosion waves.
By the end of July 1944, the entire Manhattan Project had been reorganized around building the implosion-type bomb.

The required implosion was achieved by using shaped charges with many explosive lenses to produce the perfectly spherical explosive wave which compressed the plutonium sphere.

Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, an initial test would be required. The first nuclear test took place on July 16, 1945, near Alamogordomarker, New Mexicomarker, under the supervision of Groves's deputy Brig. Gen. Thomas Farrell. Oppenheimer gave the test the code name "Trinitymarker".

Similar efforts

A similar effort was undertaken in the USSRmarker in September 1941 headed by Igor Kurchatov (with some of Kurchatov's World War II knowledge coming 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 initially did not pool their efforts. A British project, code-named Tube Alloys, was started but did not have United States 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, Canadian and Australian scientists joined the Manhattan Project at McGill University in Montreal and at a new project site located at Chalk River, Ontariomarker, with living facilities for those working in the newly created community of Deep River, Ontario.

The question of Axis efforts on the bomb has been a contentious issue for historians. It is believed that efforts undertaken in Germany, headed by Werner Heisenberg, and in Japan, were also undertaken during the war with little progress. It was initially feared that Hitler was very close to developing his own bomb. Many German scientists in fact expressed surprise to their Allied captors when the bombs were detonated in Japan. They were convinced that talk of atomic weapons was merely propaganda. However, Werner Heisenberg (by then imprisoned in Britain at Farm Hall with several other nuclear project physicists) almost immediately figured out what the Allies had done, explaining it to his fellow scientists (and hidden microphones) within days. The Nazi reactor effort had been severely handicapped by Heisenberg's belief that heavy water was necessary as a neutron moderator (slowing preparation material) for such a device. The Germans were short of heavy water throughout the war because of Allied efforts to prevent Germany from obtaining it, and the Germans never did stumble on the secret of purified graphite for making nuclear reactors from natural uranium.

Niels Bohr, Werner Heisenberg and Enrico Fermi were all colleagues who were key figures in developing the quantum theory together with Wolfgang Pauli, prior to the war. They had known each other well in Europe and were friends. Niels Bohr and Heisenberg even discussed the possibility of the atomic bomb prior to and during the war, before the United States became involved. Bohr recalled that Heisenberg was unaware that the supercritical mass could be achieved with U-235, and both men gave differing accounts of their conversations at this sensitive time. Bohr at the time did not trust Heisenberg, and never quite forgave him for his decision not to flee Germany before the war when given the chance. Heisenberg, for his part, seems to have thought he was proposing to Bohr a mutual agreement between the two sides not to pursue nuclear technology for destructive purposes. If so, Heisenberg's message did not get through. Heisenberg, to the end of his life, maintained that the partly-built German heavy-water nuclear reactor found after the war's end in his lab was for research purposes only, and a full bomb project had not been contemplated (there is no evidence to contradict this, but by this time late in the war, Germany was far from having the resources for a Hanford-style plutonium bomb, even if its scientists had decided to pursue one and had known how to do it).

See also


  1. The most comprehensive history of the Manhattan Project is Richard Rhodes, The Making of the Atomic Bomb (Simon & Schuster, 1986).
  2. Stephen I. Schwartz Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons. Washington, D.C.: Brookings Institution Press, 1998. Manhattan Project expenditures
  3. Rhodes, 137
  4. Rhodes, 24
  5. Rhodes, 201-203
  6. Rhodes, 251-253
  7. Rhodes, 256-260
  8. Rhodes, 262-263
  9. Frisch O. R.: "The Discovery of Fission—How It All Began". Physics Today 20 (1967), 11, pp. 43–48. Wheeler J. A.: "MIn 1933 Hungarian physicist Leó Szilárd had proposed that if any neutron-driven process released more neutrons than those required to start it, an expanding nuclear chain reaction might result. Chain reactions were familiar as a phenomenon from chemistry (where they typically caused explosions and other runaway reactions), but Szilárd was proposing them for a nuclear reaction for the first time. However, Szilárd had proposed to look for such reactions in the lighter atoms, and nothing of the sort was found. Upon experimentation shortly after the uranium fission discovery, Szilárd found that the fission of uranium released two or more neutrons on average, and immediately realized that a nuclear chain reaction by this mechanism was possible in theory. Szilárd kept this secret at first because he feared its use as a weapon by fascist governments. He convinced others to do so, but identical results were soon published by the Joliot-Curie group, to his great dismay. echanism of Fission". Physics Today 20 (1967), 11, pp. 49–52
  10. Rhodes, 185
  11. Rhodes, 306-309; 312-315>
  12. Broad, William J., "Why They Called It the Manhattan Project", New York Times, October 30, 2007.
  13. Rhodes, 322-325
  14. Rhodes, 369
  15. Rhodes, 372
  16. Rhodes, 416
  17. Rhodes, 415
  18. Rhodes, 381; 388-389
  19. Serber, Robert. The Los Alamos Primer (Los Alamos Report LA-1, compiled April 1943, declassified 1965): p. 21.
  20. Rhodes, 417
  21. Rhodes, 421
  22. Rhodes, 419
  23. In Bethe's account, the possibility of 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. The worry was not entirely extinguished in some people's minds until the Trinity test.
  24. Why They Called It the Manhattan Project,, accessed Nov 2, 2007.
  25. Natural self-sustaining nuclear reactions have occurred in the distant past (circa two billion years ago); see Natural nuclear fission reactor
  26. The Atomic Heritage Foundation—Atomic History Timeline 1942–1944


Overall, administrative, and diplomatic histories of the Manhattan Project
  • DeGroot, Gerard, The Bomb: A History of Hell on Earth, London: Pimlico, 2005. ISBN 0-7126-7748-8
  • Feynman, Richard P. "Surely You're Joking, Mr. Feynman!". W. W. Norton & Company, 1997. ISBN 978-0393316049.
  • Groves, Leslie. Now it Can be Told: The Story of the Manhattan Project. New York: Harper, 1962. ISBN 0-306-70738-1.
  • 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 0-8050-6588-1.
  • Hewlett, Richard G., and Oscar E. Anderson. The New World, 1939–1946. University Park: Pennsylvania State University Press, 1962.
  • Howes, Ruth H. and Herzenberg, Caroline L. Their Day in the Sun: Women of the Manhattan Project. Philadelphia: Temple University Press, 1999. ISBN 1-56639-719-7.
  • Jungk, Robert. Brighter Than a Thousand Suns: A Personal History of the Atomic Scientists. New York: Harcourt, Brace, 1956, 1958.
  • Norris, Robert S., Racing for the Bomb: General Leslie R. Groves, The Manhattan Project's Indispensable Man. Vermont: Steerforth Press, First Paperback edition, 2002. ISBN 1-58642-067-4.
  • Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986. ISBN 0-671-44133-7.
  • Rhodes, Richard. Dark Sun: The Making of the Hydrogen Bomb. New York: Simon & Schuster, 1995. ISBN 0-684-80400-X.
  • Kelly, Cynthia. Remembering the Manhattan Project: Perspectives on the Making of the Atomic Bomb and Its Legacy New Jersey: World Scientific, 2005. ISBN 978-981-256-040-7.
  • Kelly, Cynthia. Oppenheimer and the Manhattan Project: Insights into J Robert Oppenheimer, “Father of the Atomic Bomb” New Jersey: World Scientific, 2005. ISBN 978-981-256-418-4.
Technical histories
  • Groueff, Stephane. Manhattan Project: The Untold Story of the Making of the Atomic Bomb. Boston: Little, Brown & Co, 1967.
  • 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. New York: Cambridge University Press, 1993. ISBN 0-521-44132-3.
  • Serber, Robert. The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb. Berkeley: University of California Press, 1992. ISBN 0-520-07576-5—Original 1943, Los Alamos Report "LA-1", declassified in 1965. (Available on Wikimedia Commons).
  • Sherwin, Martin J. A World Destroyed: The Atomic Bomb and the Grand Alliance. New York: Alfred A. Knopf, 1975. ISBN 0-394-49794-5.
  • 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. See Smyth Report.
  • Yenne, William. "The Manhattan Project", Secret Weapons of World War II: The Techno-Military Breakthroughs That Changed History. New York: Berkley Books, 2003, p. 2–7.

Participant accounts
  • Badash, Lawrence, Joseph O. Hirschfelder, Herbert P. Broida, eds. Reminiscences of Los Alamos, 1943–1945. Dordrecht, Boston: D. Reidel, 1980. ISBN 90-277-1097-X.
  • Bethe, Hans A. The Road from Los Alamos. New York: Simon and Schuster, 1991. ISBN 0-671-74012-1.
  • 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 0-688-06910-X.
  • Serber, Robert. Peace and War: Reminiscences of a Life on the Frontiers of Science. New York: Columbia University Press, 1998. ISBN 0-231-10546-0.
  • Ulam, Stanisław. Adventures of a Mathematician. New York: Charles Scribner's Sons, 1983. ISBN 0-520-07154-9.

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