United States Nuclear Overview

This page is part of the United States Country Profile.

The United States became the world’s first nuclear weapon state in 1945, and remains the only state ever to have used a nuclear weapon in wartime. Today, it maintains one of the world’s largest operational arsenals: approximately 4,480 warheads, 1,740 of which are deployed. ¹

This includes an estimated 1,590 strategic warheads based in the United States and 150 nonstrategic warheads deployed in Europe, as well as 700 deployed delivery systems (i.e., intercontinental ballistic missiles (ICBMs), submarine launched ballistic missiles (SLBMs), and strategic bombers). ²

President Barack Obama declared in his 2009 Prague address that because of its central role in nuclear weapons development, the United States has a “moral responsibility” to lead global efforts seeking “the peace and security of a world without nuclear weapons.” ³ The United States was a driving force behind the negotiation of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), as well as most other major arms control and nonproliferation treaties and regimes. Under the terms of the New Strategic Arms Reduction Treaty (New START) with Russia, signed in April 2010, the United States will reduce its strategic nuclear arsenal to 1,550 operational warheads deployed on 700 delivery vehicles by February 2018. The Obama administration remained committed to advancing the goal of nuclear disarmament as declared in Prague, and in accordance with U.S. NPT commitments.

The Donald Trump administration has not formally outlined its stance on nuclear disarmament and modernization. Personal comments made by President Trump indicate a desire to expand modernization plans initiated by the Obama administration and to renegotiate essential arms control treaties with Russia, such as the Intermediate-Range Nuclear Forces (INF) Treaty and the New START Treaty. On 27 January 2017, President Trump tasked the Department of Defense with conducting a Nuclear Posture Review, to be completed by 2018, which should clarify U.S. nuclear policy under the Trump administration. ⁴

In addition to its nuclear weapon capabilities, the United States is the world’s largest producer of nuclear power, accounting for more than 30 percent of the world’s nuclear generated electricity, with 99 operating nuclear power reactors, four under construction, and at least four other nuclear reactor licenses approved or awaiting approval. ⁵ The four nuclear reactors under construction are currently in limbo, as the company managing their construction, Westinghouse Electricity Co., filed for bankruptcy in March 2017. ⁶

Strategic Nuclear Weapons

According to the most recent New START data exchange (1 March 2017), the United States deploys 1,411 strategic warheads on 673 Minuteman ICBMs, Trident II D-5 SLBMs, and B-52H and B-2A bombers. ⁷ The actual number of deployed U.S. warheads is likely higher since the treaty counts one strategic bomber as one operationally deployed warhead even though, for example, the B-2 bomber can carry up to 16 warheads. ⁸ A December 2016 estimate by Hans Kristensen and Robert Norris put the actual number of operational U.S. strategic warheads at roughly 1,590. ⁹

Land-based

400 ICBMs are deployed at three different Air Force bases, each with three squadrons that control 50 missile silos apiece—50 silos, scattered throughout the bases, are empty but ready to load stored missiles if necessary. The three bases operate the ICBMs from five launch control centers located in Colorado, Nebraska, Wyoming, North Dakota, and Montana. ¹⁰ There are an additional 270 non-deployed Minuteman ICBMs in storage. ¹¹ Under normal circumstances, deployed missiles carry a single 300-335 kiloton warhead (W78 or W87), though about half are capable of being MIRVed—that is, they can carry multiple independently targetable re-entry vehicles. ¹²

To meet New START levels, the Air Force reduced the ICBM force to from 450 to 400 deployed missiles. The last of the 50 Minuteman III ICBMs slated for removal was taken out of its silo at F.E. Warren AFB on 2 June 2017. ¹³ The 50 excess silos will be kept “warm” if it becomes necessary to reload the missiles. ¹⁴ Under New START, the Air Force must destroy all previously deactivated ICBM silos. By August 2014, the Air Force had destroyed 103 deactivated silos. ¹⁵ 50 silos at F.E. Warren Air Force Base in Wyoming and four silos at Vandenberg Air Force Base in California are awaiting dismantlement. ¹⁶

Air-based

The Air Force currently operates 18 B-2s and 70 B-52Hs that are nuclear capable. To comply with New START requirements limiting the United States to 60 nuclear-assigned bombers, only 16 B-2A and 44 B-52H strategic bombers have a nuclear mission on any given day. ¹⁷ The Air Force has extended the operational lifetime of its B-52s to 2040 and its B-2A’s to 2058, though the actual number of years they remain in service will depend on future congressional appropriations. ¹⁸ B-52s carry air-launched cruise missiles (ALCMs), while the B-2s carry B61 and B83 gravity bombs (with a yield of 1.2 megatons, the B83 is the largest nuclear weapon remaining in the U.S. arsenal). It is estimated that about 1,000 nuclear weapons are assigned to the U.S. bomber force, but only 300 are typically deployed. ¹⁹

Sea-based

The Navy’s 14 Ohio-class nuclear-powered ballistic missile submarines (SSBNs) carry Trident II D5 SLBMs. The D5 SLBM will be replaced in 2017 by “D5LE” missiles with greater longevity, accuracy, and flexibility. The D5LE will arm the Ohio-class submarines until the end of their service life in 2042. ²⁰ Of the 14 submarines, 12 are considered operational; however minor repairs and an overhaul rotation mean that only 8-10 are at sea at any given time. ²¹ In keeping with New START obligations, by 2018 the Navy will reduce the number of deployed SLBMs to 240 by deactivating 4 of the 24 missiles tubes on each SSBN. ²² Ten submarines have been converted so far, and the remaining 4 will be converted in 2017. ²³ The Trident II D5 SLBMs can carry up to 8 warheads each, but are thought on average to carry 4-5 warheads consisting of two basic types – the 100kt W76-0 and the 455kt W88. ²⁴

Currently, each SSBN conducts, on average, two to three patrols a year (down from three to four patrols a decade ago), with an average patrol lasting 77 days. Most patrols now occur in the Pacific Ocean, possibly reflecting U.S. nuclear war planning vis-a-vis China, North Korea, and Russia. ²⁵

Nonstrategic Nuclear Weapons

The U.S. inventory of nonstrategic (or tactical) nuclear weapons consists of approximately 500 B61 gravity bombs, 150 of which are deployed in Europe at six bases in the remaining North Atlantic Treaty Organization (NATO) states that host them: Belgium, Germany, Italy, the Netherlands, and Turkey. ²⁶

Nuclear Force Modernization

The United States is currently modernizing its entire nuclear arsenal. In 2015, the United States completed a program to upgrade and extend the lifetime of its Minuteman III ICBMs through 2030. ²⁷ In addition, the Air Force requested $9.4 billion to study a replacement for these missiles in 2013 and a $7 billion program was approved, including options to “increase survivability and reduce the requirement to keep missiles on high alert.” ²⁸ In 2016, a program was approved to move development of this new ground-based strategic deterrent into the “Technology Maturation and Risk Reduction” phase. ²⁹ The Air Force also aims to replace the current strategic bomber fleet with a new Long-Range Strike Bomber (LRS-B). The LRS-B is scheduled to begin flight testing in the mid-2020s with an anticipated operational capability toward the end of the decade. ³⁰ The United States also plans to “upgrade nuclear command and control capabilities on existing bombers; develop improved nuclear weapons (B61-12s and long-range standoff missiles, or LRSOs); and design a new heavy bomber.” ³¹

With respect to the sea-based leg of the Nuclear Triad, the United States intends to replace its Ohio-class SSBNs with the next-generation Columbia-class in the 2020s. The Columbia-class will be 2,000 tons heavier and equipped with only 16 missile tubes. Procurement of the first submarine is slated for 2021 and its deployment is slated for 2031. ³² Each new SSBN is currently estimated to cost up to $8.6 billion, a price tag that many fear will consume the Navy’s entire shipbuilding budget and consequently reduce the U.S. global presence. ³³

The National Nuclear Security Administration (NNSA) has also outlined a “3+2 Plan” to modernize the U.S. stockpile of nuclear warheads. ³⁴ Under the plan, sea- and land-based ballistic missiles would use any of three “inter-operable warheads,” and air-delivered weapons would use one of two warheads. In addition, the family of B61 bombs currently assigned to strategic bombers as well as dual-capable aircraft in Europe will be consolidated into one upgraded version known as the B61-12. ³⁵

An official estimate by the Congressional Budget Office (CBO) puts the cost of the DoD’s and DoE’s modernization plans at $400 billion over the next ten years. ³⁶ The CBO breaks this estimate down as follows: $189 billion for strategic nuclear delivery systems, $9 billion for tactical nuclear delivery systems and weapons, $87 billion for DoE’s nuclear weapons labs, $58 billion for DoD’s command and control, and $56 billion to account for unanticipated cost increases. ³⁷ The Arms Control Association estimated total modernization costs by type, projecting the costs of modernizing the SLBM fleet at $130 billion, the new bomber fleet around $100 billion, the new ICBMs around $90-140, and the new ALCMs about $11 billion. ³⁸ The DoD and NNSA’s internal estimates are significantly lower, projecting $230-290 billion and $300 billion, respectively, spread over the next 25 years. ³⁹ However, one group of experts extrapolates the thirty-year cost of maintaining and upgrading existing nuclear bombs and warheads at over $1 trillion. ⁴⁰

The Obama administration pushed back against critics of nuclear modernization, emphasizing that there is no contradiction between nuclear force modernization and the vision of a world free of nuclear weapons. It maintained that modernization is important to increasing the safety, security, and reliability of nuclear weapons, as well as ensuring the credibility of extended deterrence. ⁴¹ The Trump administration’s 2018 budget proposal allocates an extra $589 million dollars for nuclear force modernization. The additional funding reflects the increasing costs of the existing modernization plan set out by the Obama administration, rather than an expansion of that plan. ⁴²

U.S. nuclear doctrine has gone through several distinct phases, but while the declaratory policy (what is said publicly) has shifted over time, operational policy was relatively consistent throughout the Cold War. ⁴³ This included striking first if necessary (preemptive attack) in order to prevent the Soviet Union from launching an attack that would have precluded any coordinated, effective U.S. response. Importantly, however, the decision to use nuclear weapons has always been the president’s alone to make (apart from the pre-delegated authority to use certain air defense nuclear weapons or nonstrategic nuclear weapons allocated to NATO under very limited emergency circumstances first authorized by President Eisenhower in the late 1950s). ⁴⁴

Massive Retaliation

Early plans for nuclear war envisioned nuclear weapons as larger versions of the conventional bombs that had helped the United States to win WWII. In the days of the U.S. nuclear monopoly, if the Soviet Union had attempted to overrun Europe or challenge the United States elsewhere in the world, U.S. bombers (the only delivery system capable of carrying the very large bombs of the time) would have dropped nuclear weapons on the Soviet Union until it capitulated or was destroyed. By the early 1950s, once the Soviets were believed to have deployed significant numbers of atomic bombs of their own, nuclear deterrence began to take shape. Although the United States never ruled out striking first, the difficulty of ensuring the destruction of every Soviet nuclear weapon called for a new approach. Thus the Eisenhower administration announced in 1954 that Soviet aggression anywhere in the world would be met with massive retaliation, an unleashing of the U.S. nuclear arsenal against Soviet nuclear forces and urban and industrial targets.

Until 1960, there was no unified nuclear war plan. The Air Force, Navy, and Army, through their various commands, developed their own target maps and attack plans. Not surprisingly, this resulted in a significant degree of redundancy, with the military devoting more firepower than was actually necessary to destroy particular targets. Worse still, under the plans then in effect one service’s weapons would have destroyed another’s in any nuclear conflict, limiting the damage to the intended Soviet targets. Dissatisfied with this state of affairs, Eisenhower in 1960 ordered the creation of the Joint Strategic Target Planning Staff to develop a unified nuclear war plan.

Flexible Response

But the early unified plans still envisioned a massive strike. Doctrinal and technological limitations did not permit any flexibility. If the order for a nuclear strike had been given, almost nothing would have been withheld, regardless of the nature of the initial attack. Early plans called for attacks on targets in the Warsaw Pact and China even if they were not involved in the confrontation. This concerned President Kennedy greatly, so efforts were made to develop a more flexible range of options for the president, theoretically better suited to managing escalation in situations short of global nuclear war. In an effort to control the escalation of a nuclear conflict, options were also developed that distinguished between military targets (counterforce) and civilian and industrial targets (countervalue). In reality, the scale of damage made possible by nuclear weapons and the proximity of military targets to civilian populations would have made such distinctions meaningless in many scenarios. However, flexible response was designed to give the U.S. president nuclear options that could potentially prevent escalation into all-out nuclear warfare.

Mutual Assured Destruction (MAD)

Once the United States believed the Soviet Union had amassed enough nuclear weapons to make a preemptive attack all but impossible, U.S. strategic thinking began to shift from destruction to deterrence. If the United States could credibly threaten to destroy the Soviet Union—regardless of which country struck first—then in theory, the Soviet Union would have no incentive to launch a nuclear first strike. Robert McNamara (President Kennedy’s and then President Lyndon Johnson’s secretary of defense), developed multiple formulas for assured destruction, calculating what percentage of the Soviet military, industry, and population would have to be under credible threat of annihilation for deterrence to work. Importantly, these calculations (like all earlier ones and even those in use today), considered only the blast effects of a nuclear explosion. Significant secondary effects, such as radiation and mass fire, were excluded based on military planners’ perceptions that they would be too difficult to accurately predict. Therefore, as Lynn Eden’s groundbreaking study concluded, U.S. nuclear war plans have consistently underestimated the physical destruction and human casualties that would be caused by even a limited nuclear attack. ⁴⁵

Limited Nuclear War

By the early 1970s, U.S. policymakers feared that deterrence was weakening, and that MAD was no longer credible, especially in the context of a smaller-scale attack on NATO. The Nixon administration sought to bolster deterrence by creating options for limited nuclear war. This was an outgrowth of the earlier flexible response doctrine. There were also growing concerns that the Soviet nuclear arsenal might be approaching levels and capabilities that could enable the USSR to contemplate a successful first strike on the United States. This led to a renewed emphasis on counterforce targeting, including the deployment of multiple independently targetable re-entry vehicles (MIRVs) for ballistic missiles (which would enable one missile to destroy several others and increase the number of targets that could be covered without requiring the United States to use all its missiles). However, MIRVed missiles also created the destabilizing incentive for an adversary to launch a pre-emptive strike.

The Carter and Reagan administrations built on these efforts, with the Reagan administration implementing plans to “prevail” in a protracted nuclear war with the Soviet Union. Significant efforts were also made to convince the Soviet Union that no use of nuclear weapons, on any scale or for any reason, would enable a Soviet victory, regardless of how the USSR defined victory. Denying the Soviet Union the ability to use its nuclear weapons to attain military gain was considered essential to preventing a nuclear war in the first place.

Counterproliferation and Beyond

The end of the Cold War diminished concerns about an intentional nuclear war between the superpowers, but even as the number of U.S. nuclear weapons declined dramatically—from 21,392 operational weapons in 1990 to fewer than 4,500 today—there was no wholesale rethinking of the purpose of the U.S. nuclear arsenal. The Clinton administration instituted a symbolic de-targeting plan that kept wartime targets out of ICBM guidance systems in peacetime, so that in the event of an accidental launch they would only strike the ocean. The George W. Bush administration took a different and controversial approach, however, returning China to the U.S. nuclear war plan (it had been removed by the Reagan administration) and indicating in its Nuclear Posture Review (NPR) that the United States would consider using nuclear weapons in a broad range of “rogue state” scenarios.

The Obama administration returned to a more conservative approach to nuclear doctrine in its 2010 NPR. But even as President Obama embraced the goal of seeking a world without nuclear weapons, and negotiated an arms reduction treaty with Russia, his administration did not make fundamental changes to U.S. nuclear doctrine. On 19 June 2013, more than two years after releasing its NPR, the administration released an unclassified summary of its “Nuclear Weapons Employment Strategy,” which “affirms that the United States will maintain a credible deterrent, capable of convincing any potential adversary that the adverse consequences of attacking the United States or our allies and partners far outweigh any potential benefit they may seek to gain through an attack.” ⁴⁶ While continuing to express its intention to reduce the role of nuclear weapons, the Obama administration declined to specify that the sole purpose of the U.S. nuclear arsenal was to deter or respond to a nuclear attack. Instead the new strategy said that the “the United States will only consider the use of nuclear weapons in extreme circumstances to defend the vital interests of the United States or its allies and partners. The guidance narrowed U.S. nuclear strategy to focus on only those objectives and missions that are necessary for deterrence in the 21st century. In so doing, the guidance took further steps toward reducing the role of nuclear weapons in our security strategy.” ⁴⁷

Statements made by President Trump seem to indicate a personal desire for an expansion of the U.S. nuclear arsenal, which would be a reversal from decades of reductions in U.S. nuclear weapons. However, a new Nuclear Posture Review is underway and its completion in 2018 will set out a clearer and more detailed plan for U.S. nuclear strategy under President Trump. ⁴⁸

The Manhattan Project

Fearful of Nazi Germany’s possible pursuit of the atomic bomb, President Franklin D. Roosevelt, at the urging of concerned scientists, authorized in 1940 the first government-funded research into the military potential of nuclear energy. To consolidate and coordinate the effort, the Manhattan Engineering District was established in 1942. Informally known as the Manhattan Project, this massively funded top-secret project was managed by the Army Corps of Engineers. It was led by Brigadier General Leslie R. Groves, with University of California-Berkeley physicist J. Robert Oppenheimer in charge of the scientific effort. The Manhattan Project brought together the country’s top physicists—alongside allied scientists from the United Kingdom and Canada—at a barren mesa in Los Alamos, New Mexico. The U.S. government also constructed massive industrial complexes in southeastern Washington State (to manufacture plutonium), and in a sparsely populated corner of Tennessee (to enrich uranium). These efforts to produce weapons-grade material consumed nearly all of the $2 billion (in then-year dollars) spent on the Manhattan Project. ⁴⁹ Wartime personnel at the Oak Ridge site (as the Tennessee facilities came to be known) peaked at 75,000, almost none of whom knew that they were working to build a nuclear weapon. ⁵⁰

At Los Alamos, the scientific teams decided on two different bomb designs: a gun-type weapon, which utilized highly enriched uranium, and an implosion weapon, which utilized plutonium. The latter design was used in the world’s first nuclear explosion—the Trinity test on 16 July 1945 near Alamogordo, New Mexico. The gun-type design was considered so reliable that it was never subjected to a full-scale test.

On 6 August 1945, the United States dropped a gun-type bomb nicknamed “Little Boy” over Hiroshima, Japan (with an estimated explosive yield of 15 kilotons), killing between 60,000 and 80,000 people immediately, and up to 50,000 more from injury and radiation by the end of 1945. The “Fat Man” bomb that destroyed Nagasaki on 9 August used the implosion design (estimated yield 21 kilotons), killing approximately 40,000 instantly and terminally injuring another 10,000.

Post-War Developments

After the war, there was substantial debate in Washington over whether the nuclear program should continue to be managed by the military or turned over to a civilian agency. This debate was resolved by the Atomic Energy Act of 1946, which transferred control of the U.S. atomic program to the new civilian Atomic Energy Commission (AEC), effective 1 January 1947. In 1953, President Dwight D. Eisenhower announced the Atoms for Peace program, through which the United States would, with requisite safeguards, promote the peaceful uses of nuclear technology, hoping that “the miraculous inventiveness of man shall not be dedicated to his death, but consecrated to his life.” ⁵¹ While Atoms for Peace established many of the key elements of the current nonproliferation regime, such as the International Atomic Energy Agency (IAEA) and the concept of safeguards, it also spread dual-use nuclear materials and technology around the world. Some recipients of Atoms for Peace assistance—such as India and South Africa—would divert peaceful U.S. nuclear assistance to military nuclear programs.

The Expansion of the Arsenal

The Cold War, which arguably began with the end of the Second World War, significantly intensified throughout the 1940s. By early 1950, the United States possessed more than 200 atomic bombs, but it no longer had monopoly control of nuclear weapons, as the Soviet Union had tested its first nuclear device in August 1949. Despite the emphatic opposition of some key nuclear scientists, including Albert Einstein and J. Robert Oppenheimer, the United States embarked on an accelerated program to develop the even more powerful hydrogen bomb. The AEC’s General Advisory Committee, which Oppenheimer chaired, recommended against hastily developing the hydrogen bomb, “argu(ing) that a higher morality should bar the pursuit of knowledge” of such a genocidal weapon. ⁵² Atomic weapons could sufficiently deter the use of the hydrogen bomb, the group reasoned, even if the Soviets developed one. ⁵³ Ultimately, however, fearful of Soviet technological advances, the U.S. government moved forward with the hydrogen bomb program and detonated the first thermonuclear device on 1 November 1952 at Enewetak Atoll, with a yield of 10.4 megatons. On 1 March 1954 the United States detonated the first deliverable thermonuclear bomb at Bikini Atoll, the largest U.S. nuclear test ever at 15 megatons (greatly exceeding its predicted yield of 6 megatons). In close pursuit, the Soviets detonated their first true hydrogen bomb on 23 November 1955. ⁵⁴

The hydrogen bomb project was part of the Eisenhower administration’s “New Look” military program, which emphasized mass production of nuclear weapons (and especially tactical nuclear weapons). Eisenhower favored nuclear over conventional weapons production, mistakenly believing a defense centered on nuclear weapons would be significantly less expensive than conventional weapons (the concept was promoted with the phrase “a bigger bang for a buck.”) ⁵⁵ During peak production in 1959 and 1960, the United States built more than 7,000 new nuclear warheads and bombs a year—mostly tactical nuclear weapons—equaling a rate of approximately 20 weapons produced per day. ⁵⁶ The stockpile reached a peak of more than 31,000 operational warheads and bombs in 1967, “because each military branch wanted a special nuclear weapon for practically every conceivable mission.” ⁵⁷

By the early 1970s, the United States deployed more than 7,000 nuclear weapons in Europe—to be used in defending NATO—as well as more than 2,000 in the Pacific states, including Japan, Guam, and Taiwan. Aircraft carriers, cruisers, destroyers, frigates, and submarines routinely carried an additional 3,000 nuclear weapons, totaling 38 types of nuclear weapon systems deployed abroad. However, owing to strict U.S. operational secrecy the weapons’ host nations “did not always know they were there.” ⁵⁸

Until 1964, two large gaseous diffusion plants produced the highly enriched uranium used in many of these weapons, the K-25 Plant at Oak Ridge and another facility in Portsmouth, Ohio. Fourteen different reactors in Washington State and South Carolina produced weapon-grade plutonium, though nine of these were shut down during the 1960s after officials determined they were no longer needed; the remaining five, which also produced tritium, did not cease production until 1987. Even with the high demand for nuclear weapons through the 1960s, as well as a renewed emphasis on nuclear weapons in the 1980s, the frenzied production of these fissile materials—which was not driven by any specified, finite requirement—grossly outpaced the military need for them (leading to long term and very expensive programs to “clean up” the facilities where fissile materials were manufactured and secure them against unauthorized use). In all, the United States produced 745.3 metric tons of plutonium and 103.5 metric tons of highly enriched uranium. The United States has not produced any fissile materials for nuclear weapons since 1987, and, even after downblending or marking for downblending about 141 tons of HEU, there is still a remaining stockpile of 194 tons of HEU and 49.3 tons of weapons-grade plutonium designated as excess for national security needs. ⁵⁹

Arms Control and Disarmament

From the Trinity test of 1945 to the last U.S. test on 23 September 1992, the United States conducted 1,054 nuclear explosion tests in the atmosphere, above the atmosphere (exoatmospheric), underground, and underwater. ⁶⁰

Following the Trinity test at Alamogordo, New Mexico, the first underwater nuclear explosion (part of the Crossroads series) took place in July 1946 at Bikini Atoll in the Marshall Islands. In 1951, eager to conduct more frequent tests and reduce the considerable costs associated with operating a test site in the Pacific Ocean, the AEC opened the Nevada Proving Ground (65 miles northwest of Las Vegas), where the majority of tests over the next 40 years would take place. Significantly, officials chose Nevada over other locations even though they understood that testing there would subject surrounding states (and indeed most of the rest of the country) to significant amounts of dangerous radioactive fallout. ⁶¹ Other locations of U.S. nuclear tests included the South Atlantic Ocean (1,110 miles southwest of South Africa), Christmas Island, Johnston Island, and various locations in Alaska, Colorado, Mississippi, Nevada, and New Mexico.

In the lead-up to what would become the Limited Nuclear Test Ban Treaty (LTBT), the United States observed a testing moratorium with the Soviet Union between November 1958 and September 1961. The LTBT, enacted in 1963 following the Cuban Missile Crisis and widespread protests about the effects of radioactive fallout from aboveground testing, barred all atmospheric, above-ground, underwater, and outer space nuclear testing by the signatories (the United States, the Soviet Union, and the United Kingdom. In a concession to the U.S. military and U.S. weapons developers, it did not prohibit underground testing.

The 1962 Cuban Missile Crisis, compounded by China’s entrance into the “nuclear club” in 1964, convinced the United States that nuclear weapons themselves—and not just the negative health and environmental consequences of their testing—had to be contained.

Inspired by Ireland’s General Assembly Resolution 1380 (XIV), the United States assumed leadership negotiating what would become the Treaty on the Non-Proliferation of Nuclear Weapons, or NPT. Signed in 1968, the NPT sought to prevent the further spread of nuclear weapons by enshrining a twofold bargain: the nuclear weapon states pledged to negotiate an early end to the arms race and to work towards nuclear disarmament (Article VI), in exchange for non-nuclear weapon states’ pledges to forego nuclear weapons of their own (Article II). Non-nuclear weapon states in compliance with the NPT were granted an “inalienable right” to “develop research, production and use of nuclear energy for peaceful purposes without discrimination” (Article IV). The NPT entered into force on 5 March 1970, and all but three states would eventually become a party to it. ⁶²

With parties to the NPT required to ensure exports of certain nuclear-related goods to non-nuclear weapon states were subject to IAEA safeguards, the United States, along with fourteen other supplier states, met to create the Nuclear Exporters Committee (or Zangger Committee) in 1972. The Committee’s aim was to reach a common understanding on precisely what nuclear materials and related equipment should be subject to safeguards as a condition for supply. Following India’s peaceful nuclear explosion in 1974, the United States led the effort to establish the Nuclear Suppliers Group, a voluntary organization of 46 nuclear supplier states, to better coordinate members’ export control policies and control commerce in sensitive nuclear materials and technologies. ⁶³

Even before the entry-into-force of the NPT, the United States and the Soviet Union began, in November 1969, negotiation of the Strategic Arms Limitation Talks (SALT). The SALT process produced the May 1972 Anti-Ballistic Missile Treaty, limiting strategic missile defenses to 200 interceptors and two sites each (later reduced to one site by a 1974 protocol; in December 2001, the George W. Bush administration notified Russia of its intention to withdraw from the ABM Treaty in order to deploy a missile defense system in Alaska and California). In an “Interim Agreement” both states also pledged not to construct new ICBM silos, not to increase the size of existing silos “significantly,” and to cap the number of nuclear-armed submarines and the number of launch tubes a nuclear-armed submarine could carry. ⁶⁴

The second round of SALT talks, signed in June 1979, limited both sides to 2,250 delivery vehicles (e.g., an ICBM silo, an SLBM launch tube, or a heavy bomber). Both sides pledged to adhere to the SALT II agreement while awaiting its entry-into-force, and during this time, President Jimmy Carter sought to negotiate a Comprehensive Nuclear Test-Ban Treaty (CTBT). Both SALT II ratification and CTBT negotiations were shelved after the Soviet Union invaded Afghanistan.

Under President Ronald Reagan, who on 26 May 1986 announced he would no longer abide by the un-ratified SALT II agreement, the United States and the Soviet Union negotiated and signed the Intermediate-Range Nuclear Forces (INF) Treaty in 1987. The INF Treaty eliminated an entire class of weapon systems; all nuclear and conventional ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers were now prohibited. The Reagan administration also initiated talks on the Strategic Arms Reduction Treaty (START) process, which led to the 31 July 1991 signing of the first START Treaty, intended to limit each side’s delivery vehicles to 1,600 and its accountable warheads to 6,000, of which no more than 4,900 could be ballistic missile warheads (ICBMs and SLBMs); 1,540 on heavy missiles (a restriction on Russia‘s SS-18 ICBM); and 1,100 on mobile ICBMs. The entry-into-force of START I was delayed by the collapse of the Soviet Union, which occurred just four months after the treaty’s signature. START I provisions were ultimately implemented by December 2001.

At the Cold War’s end, Presidents George H.W. Bush and Mikhail Gorbachev sought a new arms control framework that would forgo lengthy arms control negotiations and ratifications in favor of “reciprocal unilateral commitments” that were politically, rather than legally, binding. This effort became known as the Presidential Nuclear Initiatives (PNIs). These commitments involved reducing nonstrategic or tactical nuclear weapons (TNWs) and delivery vehicles. They were non-verifiable, and potentially reversible, but led to the withdrawal of “perhaps 17,000 TNWs… the deepest reductions in nuclear arsenals to date.” ⁶⁵

The Bill Clinton administration revived efforts to negotiate a CTBT. U.S. and Russian acceptance of a “zero yield” CTBT revived efforts at the Conference on Disarmament, which produced the basis for the treaty text in 1995, and a final treaty was approved by the General Assembly in 1996. In September of that year the United States became the first signatory to the CTBT, but the U.S. Senate rejected ratification in 1999, effectively halting global progress towards the treaty’s entry-into-force. ⁶⁶

Efforts to ratify START II, which was signed in January 1993, were thwarted by the 2002 U.S. withdrawal from the ABM Treaty. In turn, the failure to ratify START II prevented the beginning of START III negotiations, which Presidents Bill Clinton and Boris Yeltsin had agreed to in March 1997. The START process was temporarily replaced by the 2002 Strategic Offensive Reduction Treaty (SORT, or Moscow Treaty), signed by Presidents George W. Bush and Vladimir Putin. But SORT lacked START’s specific counting rules, verification arrangements, and irreversibility. On 5 February 2011, New START replaced SORT.

While the Obama administration was committed to pursuing further reductions with Russia as part of its commitment to seeking “the security of a world without nuclear weapons,” Russia became reluctant to agree to any cuts below 1,000 weapons, suggesting that cooperative measures beyond strategic warhead counting—such as cooperation and/or limitations on missile defenses, space weapons, and other conventional weapon systems—would be required. ⁶⁷

At the start of the Trump administration, Russia indicated that it would be willing to negotiate the extension of the New START Treaty in 2021. However, the future of the New START Treaty under Trump is unknown, as Trump has repeatedly called the Treaty “a bad deal” for the United States. ⁶⁸ The future of the INF Treaty is also uncertain under the Trump administration. The House and Senate versions of the National Defense Authorization Act (NDAA) for FY18 seek to declare Russia in “material breach” of the INF Treaty and allocate millions in funding for the research and development of U.S. intermediate-range missile systems. ⁶⁹

Early Development, Current Status, Future Plans

The 1954 amendment to the Atomic Energy Act assigned the Atomic Energy Commission (AEC) the dual function of both promoting the use of nuclear power and regulating its safety. After increasing concerns over the AEC’s ability to simultaneously regulate and promote nuclear energy, Congress abolished the AEC in 1974. The 1974 Energy Reorganization Act established the Nuclear Regulatory Commission (NRC), which became operational on 19 January 1975, with a focus on radiation protection, reactor safety, and the licensing and regulation of nuclear materials, plant siting, and other environmental protections.

The first full-scale U.S. nuclear power plant came online on 2 December 1957, at the Shippingport Atomic Power Station, approximately 25 miles from Pittsburgh, PA. Significant nuclear power construction followed, but factors including the 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in 1986 effectively ended new U.S. nuclear plant construction throughout the 1980s, 1990s, and early 2000s.

There are currently 99 commercially operating nuclear power reactors in the United States (65 PWRs and 34 BWRs), providing nearly one-fifth of total U.S. commercial energy. ⁷⁰ Four new reactors are under construction in Georgia and South Carolina. However, the company tasked with building the units, Westinghouse Electric Co., filed for bankruptcy in March 2017. ⁷¹ Westinghouse filed for bankruptcy due to issues managing the projects’ subcontractors, and is expected to break its contracts for constructing the Georgia and South Carolina plants. ⁷² Overall, the long-term future of nuclear energy in the United States is still up for debate. In addition to safety and nuclear security concerns, exacerbated by Japan’s 2011 Fukushima accident, the economic viability of nuclear power has been put into further doubt by the recent availability of cheap and abundant natural gas. ⁷³

Cooperative Agreements

Since the Atomic Energy Act (AEA) of 1954 legalized nuclear commerce, the United States has undertaken civil nuclear cooperation with other countries. Section 123 of the AEA established nine nonproliferation criteria required of states seeking a so-called 123 nuclear cooperation agreement with the United States, an enabling agreement required for significant nuclear cooperation to take place between the United States and other countries. ⁷⁴ As of January 2017, the United States has entered into nuclear cooperation agreements with 20 countries, as well as with the IAEA, the European Atomic Energy Community, and Taiwan. ⁷⁵ A number of new and renewal agreements are in negotiation; as discussed in this NTI issue brief, significant debate remains ongoing over whether the nonproliferation pre-conditions for 123 nuclear cooperation agreements need strengthening.