Nuclear Weapons.
The history of nuclear weapons began well before the United States entered World War II.
Spurred by the German discovery of nuclear fission announced early in 1939, scientists at several universities had confirmed the feasibility of an unimaginably powerful chain-reacting bomb and suggested how to build one. In August 1939, the émigré physicist Albert Einstein wrote a letter to President Franklin Delano Roosevelt (drafted by another émigré physicist, Leo Szilard) reporting these developments; in response, Roosevelt authorized a modest research program. In the Summer of 1941, the federal Office of Scientific Research and Development transferred this small, scattered research program to the Army Corps of Engineers. Taking charge of what became known as the Manhattan Project, General Leslie R. Groves organized a crash program of expanded research, industrial production of fissionable materials, and bomb development.
Research was consolidated at the University of Chicago's new Metallurgical Laboratory, where Enrico Fermi and his team achieved the first controlled nuclear reaction in December 1942. Chicago also developed the health and safety measures adopted throughout the project. Construction of production facilities for enriched uranium at Oak Ridge, Tennessee, and for plutonium at Hanford, Washington, proceeded in parallel. Groves picked J. Robert Oppenheimer to direct bomb development in a new laboratory at Los Alamos, New Mexico, managed by the University of California. Buildings were still going up when scientists began work in April 1943.
By 1945, Oppenheimer's team had designed and built two fission bombs. One used enriched uranium in a gun-type assembly, a design deemed so reliable as to need no proof-testing before deployment. The other depended on the newly discovered fissionable element plutonium assembled by implosion, a much less certain technique that did demand testing. A secret test, code-named Trinity, took place at Alamogordo, New Mexico, on 16 July 1945, producing energy equivalent to 21,000 tons (21 kilotons) of high explosives.
On 6–9 August 1945, the United States launched its nuclear attack on Japan, dropping the uranium bomb on Hiroshima, the plutonium bomb on Nagasaki. At Bikini Atoll in July 1946, two more plutonium bombs furnished the firepower for a test series called Operation Crossroads. Part public spectacle intended to demonstrate America's nuclear might, part attempt to assess the effect of nuclear weapons on ships, Operation Crossroads became the Manhattan Project's last hurrah.
After heated congressional debate, the Atomic Energy Act of 1946 settled responsibility for developing future nuclear weapons on a civilian agency, the Atomic Energy Commission (AEC). Civilian control of nuclear weapons remained intact when the AEC gave way in 1974 to the Energy Research and Development Administration, itself succeeded in 1977 by the Department of Energy. The Manhattan Project officially transferred its facilities to the AEC on 1 January 1947. Its remaining, specifically military components merged under the new Department of Defense as the Armed Forces Special Weapons Project (after two subsequent name changes, it eventually became the Defense Special Weapons Agency).
Of the major transferred facilities, only Los Alamos remained concerned primarily with nuclear-weapons research and development. Its former engineering division, however, had grown rapidly after moving to Albuquerque, New Mexico, in 1945. In 1949, it became the independent Sandia Laboratories, its management transferred from the University of California to Bell Laboratories. Its primary function was providing the engineering support to turn Los Alamos designs into working weapons.
With the Cold War now well under way, nuclear-weapons development became a high national priority. The AEC inaugurated its nuclear-weapons testing program in the Spring of 1948 with Operation Sandstone. Supported by a joint army-navy task force, Los Alamos scientists tested three new fission-bomb designs at Enewetak Atoll. Part of the United Nations Trust Territory of the Marshall Islands administered by the United States, Enewetak officially became the Pacific Proving Ground, which expanded in 1951 to include Bikini. When the outbreak of the Korean War threatened to disrupt schedules for Operation Greenhouse, the next Pacific test series, the AEC selected a continental test site in Nevada, first used for Operation Ranger in January 1951.
During the 1950s, annual testing alternated between Nevada, where operations were cheaper but restrictions greater, and the Marshall Islands, which served as the site for testing very-large-yield thermonuclear weapons. A Soviet atomic-bomb test in August 1949, decidedly sooner than many expected, had severely jolted American complacency. To meet the perceived challenge, Edward Teller (among others) vigorously advocated accelerated development of the hydrogen bomb, the so-called Super, based on thermonuclear fusion, the main subject of Teller's research at wartime Los Alamos. Although no one yet knew how to design such a weapon, President Harry S. Truman in January 1950 authorized a crash program.
The conceptual breakthrough came a year later, in February and March 1951, from a suggestion by the Los Alamos mathematician Stanislaw Ulam, which Teller improved and extended. A fission first stage (primary) would provide the energy to ignite the thermonuclear fuel (deuterium and tritium, the heavy isotopes of hydrogen) in a second stage (secondary). In essence, the Ulam-Teller idea was to couple the primary's energy to the secondary via X-rays. Hydrogen bombs (H-bombs) promised yields measured in megatons rather than the kilotons of fission bombs.
Although not based on the Ulam-Teller principle, the Greenhouse George test in May 1951 showed that a fission detonation could indeed ignite small amounts of thermonuclear fuel. Teller still deemed H-bomb progress too slow, however, and with air force support and backing from the cyclotron inventor and Nobelist Ernest O. Lawrence, he successfully lobbied the AEC for a second nuclear-weapons laboratory. It opened in September 1952 as the Livermore branch of Lawrence's Berkeley Radiation Laboratory. Two decades later it became the independent Lawrence Livermore Laboratory, still under University of California management.
The new Livermore laboratory contributed little to early thermonuclear development, which remained largely a Los Alamos enterprise. The “Mike” test in Operation Ivy at Enewetak on 1 November 1952 demonstrated a full-scale thermonuclear detonation. Sixteen months later at Bikini, on 1 March 1954, the Bravo test of Operation Castle proved the design of an aircraft-deliverable H-bomb. Twice as powerful as predicted, Bravo caused heavy fallout that injured Marshall Islanders and Japanese fishermen a hundred miles and more from ground zero. Public outcry led to the test moratorium of 1958–1961, then to the Partial Nuclear Test Ban Treaty of 1963 that ended above-ground testing. Testing moved underground.
The peak of innovation in nuclear-weapons design, with Livermore now playing a major role, came in the period 1955–1965. Despite the three-year moratorium, at least two and as many as five new types of warheads entered the stockpile each year. Gravity bombs continued to improve; the introduction in 1955 of the long-range jet-powered B-52 gave the air force a bomber that could plausibly deliver them on strategic targets. Intercontinental ballistic missiles (ICBMs) benefited even more from the trend toward efficient, lighter warheads. The first air force squadron of Atlas ICBMs became operational in 1958, followed in 1960 by the navy's nuclear-powered, missile-equipped Polaris submarine. Nuclear warheads for a variety of tactical missiles, artillery shells, torpedoes, and other munitions also proliferated.
By the mid-1960s, with nuclear-weapons development no longer posing major scientific challenges, the focus of innovation shifted from warheads to delivery systems. In 1967, the air force completed replacing its first-generation ICBMs, which used cryogenic propellants, with technically safer and more reliable missiles using solid (Minuteman) or hypergolic (Titan II) propellants. Protected in underground silos, the new missiles were ready for immediate launch. When the last Polaris submarine went to sea, also in 1967, the strategic triad of manned bombers, land-based missiles, and missile-armed submarines was in place.
The next missile generation, fitted with MIRVs (multiple independently targetable reentry vehicles), followed quickly. The air force deployed the first Minuteman IIIs in 1970, the navy its first Poseidon fleet ballistic missile systems in 1971. With land-based and sea-launched MIRV missiles, the United States acquired a reliable and essentially invulnerable means of responding to, and so deterring, nuclear attack.
Delivery systems and guidance, like warheads, continued to improve, but not radically. Although the air force's Peacekeeper missile (first deployed in 1986) and the navy's Trident system (1979) marked advances in accuracy over their predecessors, their basic character remained unchanged. Efforts to develop an antiballistic missile (ABM) system in the late 1960s and early 1970s produced only a modest deployment and were limited by the ABM Treaty of 1972. The much more ambitious Strategic Defense Initiative (Star Wars), pursued in the 1980s, cost more and produced less.
The end of the Cold War brought reductions in nuclear stockpiles and, in 1992, a halt to U.S. nuclear-weapons testing. The United States retained its nuclear arsenal at reduced levels, however, and the Department of Energy instituted a laboratory science–based “stockpile stewardship” program to insure that aging weapons would remain both safe in storage and reliable if ever required.
While the Cold War nuclear-arms race faded, nuclear weapons remained a major concern. In the 1990s, fearful that nuclear know-how might fall into dangerous hands, the Clinton administration sought to safeguard nuclear installations in the former Soviet Union. Pakistan's test of a nuclear weapon in 1998 (thereby matching India, which had exploded a nuclear device as early as 1974) stirred fears of a regional nuclear arms race.
After the September 11, 2001 terrorist attacks, the U.S. government focused on a possible nuclear attack by a rogue state or even a small terrorist band. Under President George W. Bush, the nuclear danger was subsumed into a larger preoccupation with weapons of mass destruction (WMD), including chemical and biological weapons. Allegations (later proven unfounded) that Iraqi dictator Saddam Hussein possessed WMD provided a rationale for the Iraq War of 2003. After that war, Iran and Libya agreed to UN inspections to verify that they were not developing nuclear weapons. Particular attention focused on North Korea, which in 1994 had pledged to halt nuclear-weapons research but in 2003 claimed that it possessed such weapons. While pressuring North Korea to halt its program, the Bush administration also proceeded with deployment of a missile-defense system, a limited version of President Ronald Reagan's grandiose Strategic Defense Initiative.
Fears of nuclear proliferation deepened in 2004, when Pakistan's chief nuclear scientist, Abdul Kahn, confessed that he had sold nuclear-weapons components to Iran, Libya, and North Korea. While the nuclear threat mutated into new forms, it showed no signs of disappearing as the United States moved into the twenty-first century.
See also Antinuclear Protest Movement; Civil Defense; Federal Government, Executive Branch: Department of Defense; Federal Government, Executive Branch: Other Departments (Department of Energy); Hiroshima and Nagasaki, Atomic Bombings of; Nuclear Arms Control Treaties; Nuclear Strategy.
Richard Hewlett et al., A History of the United States Atomic Energy Commission, 3 vols., 1962–1989.
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Herbert F. York, The Advisers: Oppenheimer, Teller, and the Superbomb, 1976.
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Samuel Glasstone and Philip J. Dolan, eds., The Effects of Atomic Weapons, 3d ed., 1977.
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Richard Rhodes, The Making of the Atomic Bomb, 1986.
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Barton C. Hacker, The Dragon's Tail: Radiation Safety in the Manhattan Project, 1942–1946, 1988.
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Chuck Hansen, U.S. Nuclear Weapons: the Secret History, 1988.
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Donald Mackenzie, Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance, 1990.
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Norman Polmar and Timothy M. Laur, eds., Strategic Air Command: People, Aircraft, Missiles, 2d ed., 1990.
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Barton C. Hacker, Elements of Controversy: The Atomic Energy Commission and Radiation Safety in Nuclear Weapons Testing, 1947–1974, 1994.
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