Manhattan Project

views updated May 17 2018

Manhattan Project


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 (18851962) 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 (18981964) 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 (18791955). 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 (19041967) 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 (19181988), 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 (19011954) 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.



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).


Los Alamos National Laboratory. Manhattan Project History. "The Italian Navigator Has Landed in the New World. Secret Race Won with Chicago's Chain Reaction" <> (February, 24, 2003).

National Atomic Museum, Albuquerque, New Mexico. "The Manhattan Project." <> (February 24, 2003).


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Manhattan Project

views updated May 09 2018


The Manhattan Engineer District, a secret U.S. government project begun in 1942 to develop an atomic bomb, was managed by Brigadier General Leslie Groves and undertaken by the U.S. Army Corps of Engineers. Under-taken at the urging of physicists Leo Szilard, Eugene Wigner, Edward Teller, Enrico Fermi, and Albert Einstein, the project responded to the threat of atomic weapon development by Nazi Germany. Ultimately, the U.S. effort brought together intelligence operatives, leading physicists, chemists, and engineers, as well as thousands of managers and workers at four major sites.

The best known of these sites, Los Alamos, in New Mexico, was the scientific and design headquarters of the project. Directed by the physicist J. Robert Oppenheimer, the Los Alamos site developed the theoretical knowledge behind the bomb and pieced together the designs for the two types of devices used on the Japanese cities of Hiroshima—a uranium bomb (code-named Little Boy)—and Nagasaki—a plutonium device (code-named Fat Man)—in August 1945.

However, the lesser known sites, such as the Radiation Laboratory in Berkeley, California, the Metallurgical Laboratory at the University of Chicago, and the two atomic manufacturing centers, Oak Ridge, Tennessee, and Hanford, Washington, each made major contributions to the Manhattan Project as well. Berkeley's laboratory, the product of Ernest Lawrence's work on the physics of radiation, produced the theoretical and practical knowledge that drove the electromagnetic separation process in Oak Ridge. The Metallurgical Laboratory in Chicago, headed by Arthur Compton, created the first chain reaction, and established a pilot plant for the manufacture of plutonium, built in Oak Ridge.

Full-scale uranium separation took place in the massive industrial facilities of Oak Ridge, Tennessee. Built as a secret city, the facility drew workers from throughout Appalachia and the South with high wages and promises of housing and a better life. At the three major plants of Oak Ridge—chemical separations (K-25), electromagnetic separations (Y-12), and the plutonium pilot plant (X-10)—engineers, managers, and workers struggled to produce atomic material pure enough to power the bombs being designed and assembled at Los Alamos. The Hanford, Washington, site, built and managed by the Du Pont Corporation, comprised massive camps of workers building and manning a facility to


War has always driven technological advances. United States involvement in the two great global conflicts of the twentieth century impelled the development of weapons of a hitherto unsurpassed efficacy and sophistication. Many of the weapons developed for World War I saw their genesis in the nineteenth century and remain in use in the twenty-first.

The Springfield 1903 Rifle

The Springfield was a bolt-action (single-shot) rifle was issued to United States troops during World War I, and was in wide use during the first half of the twentieth century. The Springfield 1903 was developed after observation of weapons used during the Spanish-American War (1898). Spanish troops were armed with German Mauser 98 rifles, which were superior in many ways to those available to U.S. troops. A prototype of the Springfield was developed in 1900 and went into production in 1903 at the federally-owned Springfield Armory in Geneseo, Illinois. The gun was adapted for German-style pointed ammunition—the Springfield rounds, designated "Cartridge, Ball, Caliber .30, Model of 1906," led to the term .30-'06 (or "thirty-ought six"); this ammunition is used in countless small arms in the twenty-first century. The Springfield was so obviously modeled on the German Mauser that the U.S. government had to pay royalties to the German manufacturer Mauserwerke.

The M1 Garand

The federally-owned Springfield Armory in Geneseo was also the site of the development of the only full-power, semiautomatic standard infantry rifle used during World War II. This rifle replaced the Springfield due to its superior speed of fire—it was a clip-loading rather than a bolt-action weapon, and therefore could be fired multiple times before needing to be reloaded. The M1 Garand remains the most popular high-powered target semiautomatic in the world into the twenty-first century.

The Norden Bombsight

The Norden Bombsight (NBS), an optical precision device used to target bombs from aircraft to ground locations much more accurately than had before been possible, was one of the most secret weapons developed and used by the U.S. before and during World War II. Before it was introduced, there was no precise way to guide bombs to specific targets. Bombardiers simply dropped bombs near their intended targets. "Carpet bombing" and the "Blitzkreig" approach of bombing enemy territory guaranteed a high rate of destruction and massive civilian casualties. The Navy Bureau of Ordnance began development of the NBS in 1922. In 1932 the prototype Mark XV was introduced, and the configuration of the NBS was largely unchanged throughout its functional life. Its accuracy during Allied bombing runs made it one of the most important technical developments of World War II. It was used with the first guided bombs—the forerunners of the guided missile. The NBS was used in 1967 and 1968 in the Vietnam War before it was superceded by more accurate equipment.

The Army Signal Corps was the source of most developments in the nation's communications and electronics technology in World War II. In World War I, wire had proven its worth as a communications tool and was used in most tactical and administrative signal equipment. Radio did not lend itself to secrecy and had serious drawbacks in reliability and ease of use, and in the 1930s the Signal Corps focused on researching long-range radio capabilities. The laboratories developed compact switchboards for corps and division levels. Work on a military version of the teletype printer also began, as did development of the military field typewriter. The Army Signal Corps worked to decrease the size of vehicular radios that had to be removed and set up on the ground; infantry, cavalry, and armored divisions suffered the limitations of the equipment's stationary ground use and limited range. Equipment weight was a major concern, along with limited wave range. Navigational radio emerged from World War I: it could be used for intelligence gathering or as a means of taking bearings from fixed radio sites. This concept, first used in ships and planes, has been refined throughout the twentieth century and into the twenty-first to such a degree that it can be used by individuals and has been installed in commercially manufactured automobiles.

Marie Lazzari

create plutonium, a man-made element, for use in the Fat Man device.

Secrecy was the watchword of the project, both among workers and scientists. General Groves' system of compartmentalization meant that almost all project employees, military or civilian, had knowledge of only their small piece of the atomic puzzle, with no overview of how the entire project fit together. However, some information did make its way to the Soviet Union before the close of the war, through the efforts of Soviet agents like Los Alamos physicist Klaus Fuchs.

After the successful atomic test at Alamogordo, New Mexico, on July 16, 1945, the atomic bomb became an important implement of U.S. military and diplomatic policy. At the summit of American, British, and Soviet leaders in Potsdam, Germany, in July-August 1945, President Harry Truman warned an unsurprised Joseph Stalin of the existence of a powerful new weapon. However, the August 6, 1945, dropping of the atomic bomb on Hiroshima took the world (and many Manhattan Project personnel) by surprise. The dropping of the second bomb two days later, on August 8, demonstrated that America was willing and able to use atomic weapons again to bring about Japanese capitulation.

The decision to use the atomic bomb was made by President Truman, against the advice of scientists such as James Franck, who urged the U.S. government to warn Japan first about the atomic bomb, or to demonstrate the bomb for Japanese observers first.

The U.S. sought a target area for the bombs that would hamper the Japanese war effort and provide the Japanese with a full demonstration of the bomb's devastation. Secretary of War Henry Stimson vetoed the consideration of Kyoto as a target because of its cultural value to the Japanese people. Two cities not yet bombed, Hiroshima and Nagasaki, both major cities with military ports, were chosen instead as the first targets for the atomic bombs.

After the bombs' detonations, the wartime Japanese government, at the command of Emperor Hirohito, abandoned its plan for massive resistance to U.S. invasion and surrendered on August 14, 1945. The devastation of the bombing, which killed more than 60,000 in Hiroshima and more than 30,000 in Nagasaki, would become known only in the weeks to come. More than 100,000 people injured by the atomic bombs' blasts and radiation were forced to cope with its impact for the rest of their lives.

The significance of the Manhattan Project has been assessed from various perspectives. The historian David Kennedy has written, in Freedom from Fear, that the Project

stands as the single best illustration of the American way of war—not so much for the technological novelty of the bombs, or the moral issues they inevitably raised, but because only the Americans had the margins of money, material, and manpower, as well as the undisturbed space and time, to bring an enterprise on the scale of the Manhattan Project to successful completion. (p. 668)

On the other hand, the Project forever changed warfare, international relations, and America's sense of security. Atomic weapons in the hands of governments or terrorists created the possibility of a nuclear holocaust. That specter of mass destruction would not only affect America's defense policy but also help to shape the nation's postwar society and culture.


Kennedy, David M. Freedom from Fear: The American People in Depression and War, 1929–1945. New York: Oxford University Press, 1999.

Boyer, Paul. By the Bomb's Early Light: American Thought and Culture at the Dawn of the Atomic Age. NY: Pantheon Books, 1985.

Committee for the Compilation of Materials on Damage Caused by the Atomic Bombs at Hiroshima and Nagasaki. The Physical, Medical, and Social Effects of the Atomic Bombings. New York: Basic Books, 1981.

Groueff, Stephane. Manhattan Project: The Untold Story of the Making of the Atomic Bomb. Boston: Little, Brown and Co., 1967.

Groves, Leslie. Now it Can Be Told. New York: Harper and Row, 1962.

Jones, Vincent. Manhattan: The Army and the Atomic Bomb. Washington, D.C.: United States Army, 1985.

Sherwin, Martin. A World Destroyed. New York, Vintage, 1987.

Russell Olwell

Manhattan Project

views updated Jun 27 2018

Manhattan Project, 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.]


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.

Dennis D. Wainstock

Manhattan Project

views updated May 14 2018


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.


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.



See alsoNuclear Weapons ; World War II .

Manhattan Project

views updated May 29 2018

Manhattan Project

Nuclear scientists knew in the 1930s that there was a tremendous amount of energy locked in the atomic nucleus. The problem was how to access this energy. With the discovery of nuclear fission in Germany by Otto Hahn, Lise Meitner, and Fritz Strassmann in late 1938 and the subsequent explanation of the process by Meitner and Otto Frisch, many scientists who had been forced to flee from Europe became concerned that Germany might somehow take advantage of this discovery and develop weapons based on nuclear energy. Germany had many competent nuclear scientists, access to heavy water in Norway, quantities of uranium oxide, and a strong engineering history. In the fall of 1939, Leo Szilard, a Hungarian-born physicist who had fled Germany for America, drafted a letter with Albert Einstein to send to President Franklin Roosevelt under Einstein's signature to warn Roosevelt that weapons could be created using a nuclear chain reaction in uranium and that it was very likely that Germany had started working on a uranium bomb. This letter led to the formation of the Advisory Committee on Uranium. The committee did little, however, until Rudolf Peierls and Frisch, working in England, made detailed calculations about the feasibility of nuclear weapons and proposed some possible approaches to making an atomic bomb.

Although government support was relatively weak, important nuclear-science discoveries, unannounced for security reasons, were made in the United States in 1940 and 1941. Potential pathways for enriching 235U, the self-fissioning isotope of uranium, were developed, and Glenn Seaborg and Arthur Wahl produced plutonium, an element that had great potential for use in a nuclear weapon. In December 1941, President Roosevelt authorized the formation of the Manhattan Engineer District of the Army Corps of Engineers ("Manhattan Project" ) as the organization that would oversee the development of the atomic bomb. Groups of scientists, some of whom were already working on nuclear energy research, were organized to work on various aspects of the bomb project. One such project was called the Metallurgical Laboratory at the University of Chicago, where Italian-born physicist Enrico Fermi and other scientists worked on the construction of the first nuclear reactor, powered by uranium enriched in 235U.

The Manhattan Project officially began on September 23, 1942, when Colonel Leslie Groves was named director of the project. Groves acquired production sites at Oak Ridge, Tennessee, and Hanford, Washington, and he brought in Robert Oppenheimer, a physicist from the University of California at Berkeley, as the scientific director at Los Alamos, New Mexico. Los Alamos was to be the center of physics research, engineering, and weapons design. Oak Ridge was to be the site to enrich 235U, and Hanford was to produce plutonium in nuclear reactors. Many of the country's leading chemical and engineering firms were called in to design and construct these production facilities

Oak Ridge was to produce uranium enriched in the self-fissioning isotope 235U by gaseous diffusion of the volatile compound UF6 at the K-25 plant, a facility more than a mile long, and by electromagnetic separation at the Y-12 plant. Nuclear reactors were built at Hanford to produce plutonium from natural uranium, 238U. Processes were developed to chemically separate and purify the plutonium isotopes 239Pu and 240Pu. Scientists from Great Britain also played key roles in the efforts at Los Alamos, and they were instrumental in developing the functional design of the atomic bomb. Work went on at a feverish pace during 1943 and 1944, and it was estimated that an atomic weapon would be completed by early 1945.

In the spring of 1945, preparations began in the Pacific for the use of the atomic bomb. On May 8, 1945, Germany surrendered, and the project was then focused solely on Japan. On July 16, 1945, a test device code-named "Gadget" was detonated at the Alamogordo Bombing Range in New Mexico as part of Project Trinity, the first explosion of a nuclear weapon. The success of the first test of a nuclear weapon was a testament to the ability of the leadership of the Manhattan Project to carry out an unprecedented industrial project, with the world's most talented scientists

cooperating and focusing on a single goal. That the people involved in the Manhattan Project were able to achieve such a spectacular success working in a realm of utmost secrecy in isolated locations was a most singular achievement.

On August 6, 1945, after Japan refused to surrender unconditionally, the first atomic bomb, named "Little Boy," a 235U-based bomb, was dropped over Hiroshima, Japan. Three days later, "Fat Man," a plutonium-based weapon, was dropped on Nagasaki.

Whether Germany really attempted to build an atomic weapon is debated even today. German scientists, led by physicist Werner Heisenberg, certainly had the talent to build a device. Germany had access to large uranium mines in Czechoslovakia and produced heavy water, a form of H2O in which the hydrogen atoms have an extra neutron, in Norway. Most likely there never was a serious effort in Germany to build an atomic weapon, possibly as result of sabotage of the project by Heisenberg or because of a lack of interest by Adolf Hitler.

see also Einstein, Albert; Fermi, Enrico; Heisenberg, Werner; Meitner, Lise; Nuclear Fission; Oppenheimer, Robert; Radiation; Seaborg, Glenn Theodore.

W. Frank Kinard


Frayn, Michael (2000). Copenhagen. New York: Anchor Books.

Rhodes, Richard (1986). The Making of the Atomic Bomb. New York: Simon & Schuster.

Manhattan Project

views updated May 18 2018

Manhattan Project

The Manhattan Project is the name of the program that developed the atomic bomb in the 1940s. The United States dropped two atomic bombs on Japan in 1945 to end World War II (1939–45). Ever since then, the world has wrestled with the problem of how to prevent a nuclear war.

Nuclear potential

The atomic bomb is a military weapon based on the science of splitting the nuclei within certain elements. (The nucleus is the center of an atom, the smallest part of a chemical element.) The splitting process is called nuclear fission, and the elements that are used in the process are uranium and plutonium.

Nuclear fission was discovered by scientists in Germany in late 1938. Physicists throughout the world quickly recognized the possibility of using the enormous energy released in this reaction to build weapons. There were, however, many questions to answer about the new science and challenges to overcome before a bomb could be built.

Both Germany and England investigated the possibility of a nuclear weapon early in World War II, but the war quickly demanded their full attention. Only the United States had sufficient resources and the scientific manpower to undertake the project at the time.

The development of a nuclear weapon

The United States was fearful that Germany, led by Nazi dictator Adolf Hitler (1889–1945), might develop an atomic bomb. President Franklin D. Roosevelt (1882–1945; served 1933–45) initiated secret research to produce the first weapon. The project became known as the Manhattan Project.

In 1939, funding was increased to allow theoretical and experimental research to move more quickly. In 1942, the Office of Scientific Research and Development began overseeing feasibility studies in laboratories. By mid-1942, it was obvious that new factories would have to be built. Congress approved a special fund for the president to use for secret projects, and in December 1942 Roosevelt approved $400 million for the project. By the end of the war, funding for the project totaled an enormous and unforeseen $2 billion.

With such immense funding and pressure to produce a weapon to use during the war, General Leslie Groves (1896–1970), who was in charge of the project, initiated research in as many areas as possible at the same time. No approach was to be disregarded until proven unsatisfactory. In December 1942, physicist Enrico Fermi (1901–1954) succeeded in producing and controlling a chain reaction of fission in a reactor built at the University of Chicago.

To support further research, top-secret plants were constructed. A plutonium-generating reactor was built in Hanford, Washington . A gas-diffusion facility was built in Oak Ridge, Tennessee , and a physics research lab was constructed in Los Alamos, New Mexico .

Scientists at Los Alamos worked to overcome the technical problem of how to amass fissionable material and shape it into a bomb. Uranium and a newly created element, plutonium, were at the center of the research. Eventually, two types of bombs were developed at Los Alamos. The first bomb was tested successfully in a southern New Mexican desert at Alamogordo on July 16, 1945. The explosion shook the earth with the power of twenty thousand tons of dynamite, and it was the beginning of the atomic age.

The end of World War II

By summer 1945, Germany and Italy had surrendered to the United States and its Allies . Japan, however, was not willing to surrender, despite aggressive attacks from the United States. President Harry S. Truman (1884–1972; served 1945–53), after issuing several warnings and demands for surrender, gave orders to use the atomic bomb as a military weapon.

On August 6, 1945, the bomber Enola Gay dropped a uranium bomb on Hiroshima, Japan. It totally destroyed four square miles of the city and killed more than fifty thousand people. Then on August 9, 1945, a bomber approached Japan. This time it headed for the city of Nagasaki and dropped a plutonium bomb. It destroyed one-third of the city and killed more than forty thousand people. The Japanese surrendered days later.

The Manhattan Project

views updated May 29 2018


In 1939 scientist Albert Einstein wrote a letter to U.S. President Franklin Roosevelt encouraging government funding for atomic and nuclear fission research for use in atomic weapons. His letter was prompted by rumors that Adolf Hitler and the Nazis were close to creating an atomic bomb. Roosevelt agreed and placed General Leslie Groves and physicist J. Robert Oppenheimer in charge of the Manhattan Project two years later. The name "Manhattan Project" was the code word for the development of the atomic bomb. On July 16, 1945, the first atomic bomb was tested at the Trinity Site in New Mexico. The weapon was later used against the Japanese to end World War II.

The Manhattan Project

views updated May 29 2018


Beginning in June 1942 during World War II, the United States' Manhattan Project brought together scientists and military experts to create the world's first atomic bomb. The project began following concerns that the Nazis were close to creating effective atomic weapons of mass destruction. Led by Gen. Leslie Groves and J. Robert Oppenheimer, the Manhattan Project successfully detonated the first atomic bomb at the Trinity test site in New Mexico in July 1945.

Manhattan Project

views updated Jun 11 2018

Manhattan Project Code name given to the development of the US atomic bomb during World War 2. Work on the bomb was carried out in great secrecy by a team including US physicists Enrico Fermi and J. Robert Oppenheimer. The first test took place on July 16, 1945, near Alamogordo, New Mexico, and the next month the US Air Force dropped bombs on Japan.

Manhattan Project, the

views updated Jun 08 2018

Manhattan Project, the 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.

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