Manhattan Project

(engineering) A United States project lasting from August 1942 to August 1946, which developed the atomic energy program, with special reference to the atomic bomb.

Code name for the Anglo-American project to develop the atomic bomb. In June 1943 Churchill and Franklin D. Roosevelt agreed that development should be based at the top-secret research establishment of Los Alamos in New Mexico. Brig Gen Groves was appointed to oversee the project, but the scientific director was Robert Oppenheimer and there were other Soviet intelligence assets involved, so the details were well known to Stalin from the beginning. The first live test of an atomic bomb was on 16 July 1945.

— Jon Robb-Webb

the U.S. effort in World War II that developed the atomic bomb. The possibility of developing an atomic bomb became evident late in 1938 when scientists in Germany successfully split a uranium atom by bombarding it with neutrons. In the United States, Leo Szilard, a physicist at the University of Chicago, recognized that as a result of such nuclear fission, a critical mass of uranium could produce enough neutrons to generate a chain reaction of radioactive material culminating in an enormous nuclear explosion. Prodded by Szilard, Albert Einstein, world‐renowned German physicist who had fled to the United States, wrote to President Franklin D. Roosevelt on 2 August 1939 warning that the Nazis might develop an atomic bomb.

Roosevelt formed a committee of scientists headed first by Enrico Fermi and subsequently by Vannevar Bush (renamed the National Defense Research Committee) to study the feasibility of building such a weapon. In October 1941, this was merged into the new Office of Scientific Research and Development. In spring 1942, Ernest Lawrence of the University of California, Berkeley, demonstrated that in addition to the scarce uranium isotope U‐235, the more available U‐238 could be converted into a new element, plutonium, which was also fissionable. After the United States entered the war, Roosevelt gave the development of nuclear weapons top priority, and in August 1942 he assigned the top‐secret project to the U.S. Army Corps of Engineers. Its code name, the “Manhattan Project,” derived from the Manhattan Engineer District established to supervise the weapon's construction. The commanding officer, Maj. (later Brig. Gen.) Leslie R. Groves, spent $2 billion to develop the atomic bomb.

The Manhattan Project had four main facilities. In the basement of the unused football stadium of the University of Chicago, scientists Enrico Fermi and Arthur Compton built an atomic pile and in December 1942 produced the first chain reaction in uranium. At Hanford, Washington, a plant produced plutonium‐239 from uranium‐238. The Clinton Engineer Works at Oak Ridge, Tennessee, separated uranium‐235 from uranium‐238 through gaseous diffusion. A secret new laboratory, headed by physicist J. Robert Oppenheimer, was built in 1943 on a secluded mesa at Los Alamos, New Mexico, to design and build atomic bombs.

Secrecy was an obsession with Groves, and only a handful of the 125,000 people at the Project's four facilities understood the purpose of their work. Just a few military and congressional leaders knew the reason for the project's huge expenditures, which were concealed within War Department appropriations.

Since scientists in Britain had been working toward a bomb since 1940 and discovered the new element called “plutonium,” Roosevelt and British prime minister Winston S. Churchill cooperated in the research. However, in September 1944, the two leaders decided not to share their information with the Soviet Union. Russia initiated an intense espionage effort in Britain and the United States to aid its own program, headed by physicist Igor Kurchatov.

Soviet leader Josef Stalin learned details of the bomb's progress from Communist sympathizers, among them atomic scientist Klaus Fuchs in Britain, and David Greenglass, an American soldier stationed near Los Alamos. In a controversial trial in 1950, following Fuchs's postwar confession, Greenglass testified that his brother‐in‐law, Julius Rosenberg, and Rosenberg's wife, Ethel, had passed to the Russians atomic secrets he had obtained. The Rosenbergs were executed in 1953. (The Nazi regime did not race to build an atomic bomb, although whether this was due to pessimistic miscalculations by its leading physicist, Werner Heisenberg, or to his moral opposition to such a weapon, remains unclear.)

Following Roosevelt's death on 12 April 1945, President Harry S. Truman was told about the atomic bomb (code‐named “S‐1”) twelve days later. With Germany nearing surrender and the construction of a test device only three months away, Truman created an Interim Committee to study the use of atomic bombs against Japan.

On 31 May 1945, the Interim Committee, composed of Secretary of War Henry L. Stimson, Secretary of State designate James Byrnes, Harvard president James Conant, physicist and educator Karl Compton, Vannevar Bush, and a few others, listened to Oppenheimer predict the bomb would be equal to 2,000 to 20,000 tons of TNT and with its blast and radiation would kill perhaps 20,000 Japanese. After consulting other scientists and the Joint Chiefs of Staff, the committee agreed on 1 June 1945 that for maximum psychological effect, the atomic bomb should be used without warning against a Japanese city containing a military facility.

Not all the scientists working on the Manhattan Project agreed with this. Szilard, James Franck, and a majority of the scientists at the Chicago laboratory asserted that military use against a Japanese city was unnecessary and immoral and would start a postwar nuclear arms race. In response to their petition for a test demonstration and warning for Japan, a special scientific advisory committee—composed of Fermi, Lawrence, Oppenheimer, and Arthur Compton—met on 16 June but rejected the idea of a noncombat demonstration (the bomb might not explode, and even if it did, its lethality would not be adequately demonstrated).

On 16 July 1945, the first atomic weapon test, code‐named “Trinity,” was held on a desert bombing range at Alamogordo, New Mexico, 200 miles south of Los Alamos. Mounted on a metal tower, the test device—13.5 pounds of plutonium inside 2.5 tons of explosives—was exploded at 5:29 A.M. as Groves, Oppenheimer, Bush, and others watched in awe. The blast equaled 15,000–20,000 tons of TNT and generated a fireball visible for 60 miles.

Truman learned of the successful test while at the Potsdam Conference in Germany. After mentioning cryptically to Stalin that the United States had a new weapon, Truman on 24 July ordered preparations for use against Japan. On the 26th, he issued the Potsdam Declaration, a vague modification of unconditional surrender. When Tokyo declined to consider the offer because it did not guarantee retention of the emperor, Truman, on 30 July, ordered the Army Air Forces to use America's two atomic bombs—one uranium‐cored, the other plutonium‐cored—against Japan. On 6 and 9 August, solitary American B‐29s carried out the atomic bombings of Hiroshima and Nagasaki. The bombings, combined with the Soviet Union's declaration of war against Japan on 8 August, led Tokyo to surrender on 14 August 1945. World War II ended; the atomic age had begun.

[See also Atomic Scientists; Nuclear Weapons; Science, Technology, War, and the Military; World War II: Military and Diplomatic Course; World War II: Domestic Course; World War II: Postwar Impact; World War II: Changing Interpretations.]

Bibliography

• Martin Sherwin, A World Destroyed: Hiroshima and the Origins of the Arms Race, 1973; rev. ed. 1987.
• Leslie R. Groves, Now It Can Be Told: The Story of the Manhattan Project, 1975.
• Richard Rhodes, The Making of the Atomic Bomb, 1986.
• James G. Hershberg, James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age, 1993.
• Gar Alperovitz, The Decision to Use the Atomic Bomb—and the Architecture of an American Myth, 1995.
• Barton J. Bernstein, The Atomic Bombings Reconsidered, Foreign Affairs (January–February 1995), pp. 135–52.
• Robert P. Newman, Truman and the Hiroshima Cult, 1995.
• Dennis D. Wainstock, The Decision to Drop the Atomic Bomb, 1996

The code name for the American project set up in 1942 to develop an atom bomb. The project culminated in 1945 with the detonation of the first nuclear weapon, at White Sands in New Mexico.

See the Introduction, Abbreviations and Pronunciation for further details.

For more information on Manhattan Project, visit Britannica.com.

Manhattan Project, the secret American effort during World War II to construct an atomic bomb. Following the discovery of nuclear fission in Nazi Germany in late 1938, physicists the world over recognized the possibility of utilizing the enormous energy released by the splitting of an atom. If enough neutrons could be emitted by any given "broken" atom, such that at least one neutron struck another atom, causing it to break apart, a self-perpetuating "chain reaction" would result. Such a process, if controlled at a suitable rate, could serve as a power source, or "reactor." If a chain reaction proceeded unchecked, it could result in an explosion of unprecedented magnitude.

Several European scientists who had fled Nazi persecution in Europe felt it was their duty to alert the U.S. government to this new danger. In August 1939, the Hungarian émigré physicist Leo Szilard convinced Albert Einstein to write President Franklin D. Roosevelt and urge increased government support for research on the element most likely to support a chain reaction, uranium. By early 1940, government funding had commenced on a variety of related subjects, and in 1941 a series of studies confirmed the potential that uranium research held to create a usable weapon before the end of the war. In January 1942—only weeks after the Japanese attack on Pearl Harbor—Roosevelt gave the go-ahead to proceed with a full-scale effort to develop the atomic bomb.

By this time it was obvious that large factories would eventually have to be built. Because the work was now being done in secrecy, and considerable construction was foreseen, the Manhattan Engineer District of the U.S. Army Corps of Engineers was created in August 1942 to oversee the entire atomic bomb program. (It was initially headquartered in New York in order to be close to the fission research then being conducted at Columbia University.) The following month, Colonel Leslie R. Groves was promoted to brigadier general and given command of what was coming to be known as the Manhattan Project. Groves quickly brought in major contractors such as Stone and Webster and the Dupont Chemical Company. Less than four years after the discovery of fission, the program to build an atomic bomb had grown from a primarily academic pursuit to what was becoming, by September 1942, a prototypical example of what Dwight D. Eisenhower would later dub the "military-industrial complex." At its height a mere three years later, the Manhattan Project employed more than 130,000 men and women, having already spent more than $2 billion.

The most pressing problem immediately facing Groves was the acquisition, in an extremely short amount of time, of a quantity of fissionable material sufficient first for experimentation and thereafter for the production of at least one bomb. The kind of uranium needed to generate a chain reaction, the isotope U-235, comprised only 0.7 percent of all naturally occurring uranium, and a variety of exotic and unproven techniques were proposed for "enriching" uranium, or increasing the amount of U-235 contained in a sample. Following a period of intense debate, the scientists in November 1942 made their best guess as to which of these methods showed the most promise, choosing gaseous diffusion and electromagnetic separation. Groves immediately ordered the construction of two massive, full-scale uranium-enrichment plants. In less than three years their site at Oak Ridge, Tennessee, grew from remote farmland to the fifth largest town in the state.

In early 1941, a second path to the atomic bomb was pioneered by the discovery of a new element: plutonium. This substance did not occur in nature but could be created by irradiating common uranium. In December 1942, Enrico Fermi demonstrated this by producing the world's first controlled nuclear chain reaction in a "pile," or reactor, constructed beneath the west stands of the University of Chicago's Stagg Field. Soon, three gigantic reactors were under construction on the banks of the Columbia River near Hanford, Washington, to mass produce plutonium.

The final task remaining was to devise the actual means by which these "special nuclear materials" could be transformed into practical weapons. In late 1942, Groves placed J. Robert Oppenheimer in charge of the new weapons laboratory to be built on an isolated mesa in the desert at Los Alamos, New Mexico. Oppenheimer soon managed to assemble a virtual "dream team" of scientists drawn from around the world. Relatively little difficulty was encountered in the design of a uranium weapon. One piece of U-235 could be fired at another in a gun barrel, such that together they would form a critical, or explosive, mass. For technical reasons this crude method was unsuitable for plutonium, however, and, ultimately, a new technique called implosion was conceived, wherein a small sphere of plutonium was rapidly compressed to critical mass by conventional high explosives.

There had never been much doubt that "Little Boy," the gun-type uranium weapon, would work, and on 14 July 1945 it was shipped from Los Alamos to begin its journey westward toward Japan. Because the implosion process was so novel, however, a test of the plutonium design was held near Alamagordo, New Mexico, on 16 July 1945. This test, named "Trinity" by Oppenheimer, exceeded the expectations of almost every scientist at Los Alamos by exploding with a force equivalent to more than 18,000 tons of TNT. Oppenheimer later reported that the blast reminded him of a line from the Bhagavad-Gita: "Now I am become Death, the destroyer of worlds." The reaction of the test director, Kenneth Bainbridge, was more succinct: "Now we are all sons of bitches." On the morning of 6 August 1945, an American B-29 bomber dropped the uranium bomb on the Japanese port city of Hiroshima; three days later the second, plutonium device "Fat Man," was dropped on Nagasaki. Japan offered to surrender the following day. Although estimates vary, it is likely that by the end of 1945, there were at least 200,000 deaths directly attributable to the two bombings. Most were civilians. The total number of deaths after five years, including radiation and other secondary effects, may have been well over 300,000. At the beginning of 1947, control of the growing U.S. nuclear arsenal was formally transferred to the civilian Atomic Energy Commission, and in August of that year, the Manhattan Engineer District was formally disbanded.

Bibliography

Gosling, F. G. The Manhattan Project: Making the Atomic Bomb. Washington, D.C.: History Division, Department of Energy, 1999.

Hewlett, Richard G., and Oscar E. Anderson Jr. A History of theUnited States Atomic Energy Commission. Vol. 1: The New World, 1939–1946. University Park: Pennsylvania State University Press, 1962. Comprehensive official history.

Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon and Schuster, 1986. Pulitzer Prize–winning account focusing on the activities at Los Alamos.

The Manhattan Project was an epic, secret, wartime effort to design and build the world's first nuclear weapon. Commanding the efforts of the world's greatest physicists and mathematicians during World War II, the $20 billion project resulted in the production of the first uranium and plutonium bombs. The American quest for nuclear explosives was driven by the fear that Hitler's Germany would invent them first and thereby gain a decisive military advantage. The monumental project took less than four years, and encompassed construction of vast facilities in Oak Ridge, Tennessee, and Hanford, Washington, that were used for the purpose of obtaining sufficient quantities of the isotopes uranium-235 and plutonium-239, necessary to produce the fission chain reaction, which released the bombs' destructive energy. After a successful test in Alamogordo, New Mexico, the United States exploded a nuclear bomb on the Japanese city of Hiroshima on August 6, 1945. Three days later another bomb was dropped on the Japanese city of Nagasaki, and spurred the Japanese surrender that ended World War II.

In the 1930s and early 1940s, fundamental discoveries regarding the neutron and atomic physics allowed for the possibility of induced nuclear chain reactions. Danish physicist Neils Bohr's (1885–1962) compound nucleus theory, for example, laid the foundation for the theoretical exploration of fission, the process whereby the central part of an atom, the nucleus, absorbs a neutron, then breaks into two equal fragments. In certain elements, such as plutonium-239, the fragments release other neutrons which quickly break up more atoms, creating a chain reaction that releases large amounts of heat and radiation.

Hungarian physicist Leo Szilard (1898–1964) conceived the idea of the nuclear chain reaction in 1933, and immediately became concerned that, if practical, nuclear energy could be used to make weapons of war. Szilard, who fled Nazi persecution first in his native Hungary, then again in Germany, conveyed his concerns to his friend and contemporary, noted physicist Albert Einstein (1879–1955). In 1939, the two scientists drafted a letter (addressed from Einstein) warning United States President Franklin D. Roosevelt of the plausibility of nuclear weapons, and of German experimentation with uranium and fission. In December, 1941, after the Japanese attack at Pearl Harbor and the United States' entry into the war, Roosevelt ordered a secret United States project to investigate the potential development of atomic weapons. The Army Corps of Engineers took over and in 1942 consolidated various atomic research projects into the intentionally misnamed Manhattan Engineering District (now commonly known as the Manhattan Project), which was placed under the command of Army Brigadier General Leslie Richard Groves.

Groves recruited American physicist Robert Oppenheimer (1904–1967) to be the scientific director for the Manhattan Project. Security concerns required the development of a central laboratory for physics weapon research in Los Alamos, New Mexico. Oppenheimer's leadership attracted many top young scientists, including American physicist Richard Feynman (1918–1988), who joined the Manhattan Project while still a graduate student. Feynman and his mentor Hans Bethe (1906–) calculated the critical mass fissionable material necessary to begin a chain reaction.

Fuel for the nuclear reaction was a primary concern. At the outset, the only materials seemingly satisfactory for sustaining an explosive chain reaction were either U-235 (derived from U-238) or P-239 (an isotope of the yet unsynthesized element plutonium). Additional requirements included an abundant supply of heavy water (e.g., deuterium and tritium). At Oak Ridge, the process of gaseous diffusion was used to extract the U-235 isotope from uranium ore. At Hanford, production of P-239 was eventually made possible by leaving plutonium-238 in a nuclear reactor for an extended period of time.

In 1942, Italian physicist Enrico Fermi (1901–1954) supervised the first controlled sustained chain reaction at the University of Chicago. Underneath the university football stadium, in modified squash courts, Fermi and his team assembled a lattice of 57 layers of uranium metal and uranium oxide embedded in graphite blocks to create the first reactor pile.

The Manhattan Project eventually produced four bombs. Little Boy, the code name for the uranium bomb, utilized explosives to crash pieces of uranium together to begin an explosive chain reaction. Fat Man, the code name for the plutonium bomb, was more difficult to design. It required a neutron-emitting source to initiate a chain reaction within a series of concentric nested spheres. The outermost shell was an explosive lens system surrounding a pusher/neutron absorber shell designed to reduce the effect of Taylor waves, the rapid drop in pressure that occurs behind a detonation front and could interfere with an implosion. The next nested sphere was a uranium tamper/reflector shell containing a plutonium pit and beryllium neutron initiator. The spheres were designed to implode, causing the plutonium to fuse, reach critical mass, then start the reaction

The simple design of the uranium bomb left scientists confident of its success, but the complicated implosion trigger required by the plutonium bomb raised engineering concerns about reliability. On July 16, 1945, a plutonium test bomb code named Gadget was detonated in a remote area near Alamogordo, New Mexico. Observed by scientists wearing only welder's glasses and suntan lotion for protection, the test blast (code named Trinity) was more powerful than originally thought, roughly equivalent to 20,000 tons of TNT, and caused total destruction up to one mile from the blast center.

Protecting the secrecy of the Manhattan Project was one of the most complex intelligence and security operations during the war. At the Los Alamos facility, all residents were confined to the project area and surrounding town. Though several leading scientists knew the nature and scope of the entire project, most lab facilities were compartmentalized with various teams working on different project elements. Those who worked in the lab were forbidden to discuss any aspect of the project with friends or relatives. Military security personnel guarded the grounds and monitored communications between research teams. Official communications outside of Los Alamos, especially to the other Manhattan Project sites, were coded and enciphered. Mail was permitted, but heavily censored. Since the actual location of the Los Alamos facility was secret, all residents used the clandestine address "Box 1663, Santa Fe, New Mexico," for correspondence.

Communities were created around other project sites as well. The government created the towns of Oak Ridge and Hanford, relocating thousands of area residents before beginning construction. The towns, thus secured for facility personnel and their families, placed severe restrictions on civilian activities. In some areas, private telephones and radios were prohibited. Residents were encouraged to use simple pseudonyms outside of the lab. Children did not use their full names in school in Oak Ridge, Tennessee.

Managing several different facilities, spaced nearly two thousand miles apart, raised some significant security challenges. Communication was limited, and incoming and outgoing traffic from facility areas was closely monitored. Security of key documents was a constant concern. The isolated locations of the sites helped to insulate them from enemy espionage. However, the separate locations were also a key security strategy. Breaking the Manhattan Project into various smaller operations prevented jeopardizing the entire project in the event of a nuclear accident. The compartmentalization of such projects remains a common practice.

On August 6, 1945, an American B-29 "Flying Fortress," the Enola Gay, dropped the uranium bomb over Hiroshima. Sixty thousand people were killed instantly, and another 200,000 subsequently died as a result of burn and radiation injuries. Three days later, a plutonium bomb was dropped over Nagasaki. Although it missed its actual target by over a mile, the more powerful plutonium bomb killed or injured more than 65,000 people and destroyed half of the city. Ironically, ground zero, the point under the bomb explosion, turned out to be the Mitsubishi Arms Manufacturing Plant, at one time the major military target in Nagasaki. The fourth bomb remained unused.

Many Manhattan Project scientists eventually became advocates of the peaceful use of nuclear power and advocates for nuclear weapons control.

Further Reading

Books

Fermi, Rachel, and Esther Samra. Picturing the Bomb: Photographs from the Secret World of the Manhattan Project. New York: H. N. Abrams, 1995.

Norris, Richard. Racing For the Bomb: General Leslie R. Groves, the Manhattan Project's Indespensable Man. South Royalton, VT: Steerforth Press, 2002.

Rhodes, Richard. The Making of the Atomic Bomb. New York: Touchstone, 1995 (reprint).

Electronic

Los Alamos National Laboratory. Manhattan Project History. "The Italian Navigator Has Landed in the New World. Secret Race Won with Chicago's Chain Reaction" <http://www.lanl.gov/worldview/welcome/history.shtml> (February, 24, 2003).

National Atomic Museum, Albuquerque, New Mexico. "The Manhattan Project." <http://www.atomicmuseum.com/tour/manhattanproject.cfm> (February 24, 2003).

The code name for the effort to develop atomic bombs for the United States during World War II. The first controlled nuclear reaction took place in Chicago in 1942, and by 1945, bombs had been manufactured that used this chain reaction to produce great explosive force. The project was carried out in enormous secrecy. After a test explosion in July 1945, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki.

Several innovations in science and technology, such as radar, early computers, large liquid-fueled rockets, penicillin, and the insecticide DDT, came in response to military needs during World War II. Of these, the construction of the atomic bomb and the subsequent harnessing of nuclear energy are probably the most dramatic scientific and technical results of the scientific effort during the war -- although in terms of winning the war, radar and computers were both more important.

Atomic weapon development originated with scientists. Because of fear that Nazi Germany might develop an atomic bomb -- later proven unfounded -- Leo Szilard persuaded Albert Einstein to write a letter to U.S. President Franklin D. Roosevelt, in which Einstein suggested that the fission of uranium could be used to produce an atomic explosion. This letter resulted in the establishment of the largest single enterprise in the history of science up to that time. The operation, later known as the Manhattan Project, comprised 37 installations in 19 states and Canada, and employed 43,000 people. It ran on a budget of $2.2 billion. A large number of physicists, among them the best European scientists who had fled the Nazis, joined the project. Physicists were recruited from college campuses all over the United States as well.

New cities emerged as a direct result of the Manhattan Project. Los Alamos, New Mexico, was the site where the atomic bombs were designed and built under the directorship of the physicist J. Robert Oppenheimer. The project in 1943 took over the Los Alamos Ranch School, a residential school for boys emphasizing outdoor activities. The school had an enrollment of 50 students. With new buildings constructed on the site and on nearby property, the facility came to house 5700 scientists, technicians, and their families by 1945. Oak Ridge, Tennessee, where the gaseous diffusion plant for the separation of uranium-235 from uranium-238 was located, reached a population of 79,000 in less than two years. Hanford in the state of Washington housed the nuclear reactors for the transmutation of uranium-238 to plutonium-239 and reached a population of 60,000.

Notwithstanding the enormous size of the organization, the American government succeeded in keeping the whole operation a secret. Most of the employees, and even some scientists, did not know the exact aim of the organization. Secrecy was strictly enforced. Scientists traveled under assumed names. For example, Enrico Fermi was disguised as Henry Farmer, and Eugene Wigner as Eugene Wagner. All telephone conversations at Los Alamos were under surveillance and were interrupted if the military authorities judged them a threat to security. Sensitive matters were referred to by code words; plutonium was called 49 (94 is its atomic number) and uranium "tube alloy."

The massive effort resulted in the first experimental explosion of a nuclear device in July 1945, quickly followed by the dropping of atomic bombs on the Japanese cities Hiroshima and Nagasaki on August 6 and 9, respectively, 1945. By then Germany had surrendered and Japan was nearly defeated, but the dramatic death and destruction of whole cities propelled Japan into surrendering without an Allied invasion.

After the war, the facilities continued at first to design and make nuclear weapons, but gradually Los Alamos became a national physics laboratory with many projects. Oak Ridge is also a national laboratory, but continues in the business of enriching uranium for peaceful nuclear power projects, while Hanford was dismantled (except for a museum about the Manhattan Project), becoming a major environmental problem of the 21st century.