Manhattan Project
The Manhattan Project was a pivotal World War II initiative undertaken by the United States to develop nuclear weapons, spurred by fears that Nazi Germany was pursuing similar capabilities. This large-scale research and engineering effort began in response to a letter from physicists Albert Einstein and Leo Szilard, which warned President Franklin D. Roosevelt about the potential for nuclear fission to be weaponized. Key locations for the project included Los Alamos in New Mexico for bomb development, Oak Ridge in Tennessee for uranium enrichment, and Hanford in Washington for plutonium production. Scientists created two types of atomic bombs: "Little Boy," which used uranium, and "Fat Man," which used plutonium. The successful testing of these bombs culminated in their deployment over Hiroshima and Nagasaki in August 1945, resulting in significant loss of life and hastening Japan's surrender. The outcomes of the Manhattan Project ushered in the nuclear age, establishing the United States as a dominant global power and shaping international relations during the ensuing Cold War. The legacy of the project continues to provoke ethical discussions and cultural reflections, including recent media portrayals that explore its historical impact and the moral dilemmas faced by its key figures.
Manhattan Project
Identification U.S. Army research project, officially named the Manhattan Engineering District, that designed and built the world’s first nuclear weapons
The Manhattan Project ushered the world into the nuclear age, demonstrating that the energy released by nuclear fission could be triggered and controlled. It produced the two atomic bombs dropped on Japan at the end of World War II; achieved the first artificial nuclear chain reaction and laid the scientific and engineering foundations for the generation of electricity from nuclear power; and advanced the art of nuclear chemistry, achieving transmutation of the elements and the artificial production of radioactive isotopes on a practical scale.
Otto Hahn and Lise Meitner discovered uranium fission during the late 1930s. The immense amount of energy released in the process opened up the possibility that uranium could be used as an explosive of unprecedented destructive power. In a letter delivered to President Franklin D. Roosevelt on October 11, 1939, physicists Albert Einstein and Leo Szilard alerted the president that Nazi Germany might be researching nuclear fission to develop a nuclear weapon and that the United States should follow suit. At Roosevelt’s direction, an aide set up an Advisory Committee on Uranium to keep the president informed as research continued.
In June 1942, roughly six months after the US entered World War II (1939–45) against Nazi Germany, the Empire of Japan, and the other Axis Powers, the committee reported that the Nazi's research had advanced to the point that construction of a pilot plant and preliminary design of production plants for fissionable material were possible. It recommended that the U.S. Army Corps of Engineers begin construction on its own program. President Roosevelt agreed. An unnamed engineering district under the direction of Colonel James C. Marshall was created on June 18, 1942, to carry out this responsibility.
In September of 1942, Colonel Marshall was promoted, reassigned overseas, and relieved by Brigadier General Leslie R. Groves. The district was now designated the Manhattan Engineering District after the location of Colonel Marshall’s headquarters; General Groves made his new headquarters in Washington, D.C.
The greatest challenge facing the Manhattan Project was the accumulation of sufficient quantities of fissionable material. Physicists had identified two very likely candidates: the natural isotope uranium-235 (U-235), and the artificial isotope plutonium-239 (Pu-239). Natural uranium is only seven-tenths of 1 percent U-235; the remainder is overwhelmingly uranium-238 (U-238), which could not be made to fission with any process available during the 1940’s. U-235 cannot be chemically separated from U-238; it must be physically separated using processes that rely on the tiny 1.2 percent difference in mass between the two isotopes. Plutonium is an artificial element created by bombarding U-238 with neutrons to form U-239, which then radioactively decays into Pu-239. Producing either of these two materials in industrial quantities seemed so difficult and uncertain that it was decided to pursue both in parallel. The plutonium effort was assigned to the Hanford Nuclear Reservation, and the uranium effort was assigned to the Clinton Engineering Works at Oakridge, Tennessee. Design and construction of the nuclear weapons themselves was assigned to a new laboratory known only as Los Alamos.
Hanford Nuclear Reservation
Natural uranium contains enough U-235 to support a controllable fission chain reaction under the proper circumstances. The copious amounts of neutrons emitted by the reaction bombard U-238 atoms and transmute them into Pu-239. The Pu-239 can then be chemically separated and used as raw material for nuclear weapons. A team of scientists and engineers led by Enrico Fermi created the first sustainable fission chain reaction in uranium on December 2, 1942. Within weeks, the Manhattan Project acquired 780 square miles of vacant land in south-central Washington State for the Hanford Engineer Works. Construction of three nuclear reactors and four chemical separation plants began in late 1942. In the next three years, this huge facility produced enough Pu-239 for three nuclear devices.
Clinton Engineering Works
The Manhattan Project settled on two competing methods to separate U-235 from U-238. In electromagnetic separation, the uranium was rendered into a gas (uranium hexafluoride), the gas ionized and then electrically propelled through a magnetic field. In traveling through the magnetic field, the lighter U-235 followed a more sharply curved path than the U-238. The two isotopes ended their journeys at two different places. In gaseous diffusion, the uranium hexafluoride was pumped through a series of porous barriers with millions of submicroscopic openings per square inch. The gas molecules containing U-235 trickled through the barriers at a slightly higher rate than those with U-238. After passing through several thousand such barriers, the concentration of U-235 was significantly enhanced.
The Manhattan Project acquired 59,000 acres of land along the Clinch River in eastern Tennessee in September, 1942, for the Clinton Engineer Works, anchored by the town of Oak Ridge. The electromagnetic separation complex was known as Y-12; it eventually employed more than 4,800 people. The gaseous diffusion complex was known as K-25, a single four-story building with 43 acres under one roof. In three years, Y-12 and K-25 together separated enough U-235 for a single bomb.
Los Alamos
The Manhattan Project acquired the Los Alamos Ranch School outside Santa Fe, New Mexico, to use as the site for the bomb development laboratory. The University of California was contracted to operate the laboratory. J. Robert Oppenheimer was appointed laboratory director. Los Alamos produced two different types of bomb. “Little Boy” used a gun to fire a uranium slug into a subcritical mass of uranium at high velocity. Once the slug and subcritical mass joined, an explosive fission chain reaction was spontaneous. “Fat Man” used chemical explosives to squeeze a subcritical mass of plutonium to a density high enough for explosive fission to occur. The Little Boy design was considered so reliable that no testing was required. The Fat Man design was successfully tested at 5:30 a.m. on July 16, 1945, at a desert site code-named Trinity near Alamogordo, New Mexico.
On August 6, 1945, at 8:15 a.m., Little Boy detonated over the Japanese city of Hiroshima, killing 145,000 people. On August 9, 1945, at 11:02 a.m., Fat Man detonated over the city of Nagasaki, killing 70,000. On August 15, 1945, the Emperor of Japan broadcast a statement to his subjects ordering the acceptance of the Allied surrender terms. The surrender documents were signed aboard the USS Missouri on September 2, 1945.
Impact
The successful conclusion of the Manhattan Project and the dawn of the nuclear age drastically altered the role of war in international relationships. It put the United States in a place of unprecedented international power and influence. When the Soviet Union joined it in the exclusive club of nuclear powers, the United States had to get used to sharing that power and influence. Deep feelings of mutual distrust and fear kept the two superpowers locked in a subdued conflict known as the Cold War that lasted until the collapse of the Soviet Union during the early 1990s. Almost all international crises since World War II have been influenced to some degree by the chilling possibility of nuclear war.
Subsequent Events
The Atomic Energy Act of 1946 placed all nuclear research and nuclear weapons development under the control of the Atomic Energy Commission, for all intents and purposes bringing the Manhattan Project to an official end. Los Alamos, Oak Ridge, and Hanford continued operations, slowly building up a stockpile of nuclear weapons. Many of the leading scientists working on the project returned to academic posts; some remained with the project to begin work on weapons exploiting thermonuclear fusion rather than fission. The world’s first thermonuclear explosion, the work of agencies succeeding the Manhattan Project, took place on November 1, 1952.
On August 29, 1949, the Soviet Union detonated its first atomic explosive device. The Soviet Union detonated its first thermonuclear device on August 12, 1953.
In Popular Culture
In November 2015 Sally Jewell, who served as the US Secretary of the Interior from 2013 to 2017, and Ernest Moniz, a nuclear physicist serving as US Secretary of Energy at that time, signed legislation creating the Manhattan Project National Historical Park. This park, run jointly by the US National Park Service and Department of Energy, included former Manhattan Project sites in Los Alamos, New Mexico; Oak Ridge, Tennessee; and Hanford, Washington.
Despite the Manhattan Project's top-secret nature during World War II, in the years after the war it quickly attracted intense interest in US popular culture. In 1947, not even two years after Japan's surrender, Norman Taurog directed a docudrama film, The Beginning or the End. While this film attempted to portray the events leading up to the creation of the first atomic bomb with a high degree of historical accuracy, the ongoing secrecy surrounding some aspects of the project resulted in a number of misrepresentations and historical inaccuracies. In subsequent years a number of other documentaries, novels, nonfiction books, plays, and films examined the Manhattan Project and the individuals involved. For example, 2023 saw the release of Christopher Nolan'sOppenheimer, a biopic starring Cillian Murphy as J. Robert Oppenheimer. The film examined Oppenheimer's central role in the Manhattan Project and the physicist's moral dilemmas toward his own role in ushering in the age of nuclear weapons.
Bibliography
Bird, Kai, and Martin J. Sherwin. American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer. Alfred A. Knopf, 2005.
Groves, Leslie R. Now It Can Be Told: The Story of the Manhattan Project. Da Capo Press, 1962.
Howes, Ruth H., and Caroline C. Herzenberg. Their Day in the Sun: Women of the Manhattan Project. Temple University Press, 1999.
Joseph, Timothy. Historic Photos of the Manhattan Project. Turner Publishing, 2009.
Kifer, Andy. "The Real History Behind Christopher Nolan’s ‘Oppenheimer.’" Smithsonian, 18 July 2023, www.smithsonianmag.com/history/the-real-history-behind-christopher-nolans-oppenheimer-180982529/. Accessed 14 Aug. 2023.
Rhodes, Richard. The Making of the Atomic Bomb. Simon & Schuster, 1986.
"The Manhattan Project in Popular Culture." Atomic Heritage Foundation, 2 Aug. 2017, ahf.nuclearmuseum.org/ahf/history/manhattan-project-popular-culture/. Accessed 14 Aug. 2023.