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Also known as: atomic weapon, thermonuclear weapon
Written by
Robert S. Norris
Dr. Norris was a senior research associate with the Natural Resources Defense Council in Washington, DC from 1984 to his retirement in 2011. His principal areas of expertise include writing and research.
Robert S. Norris ,
Thomas B. Cochran
Dr. Thomas B. Cochran is a consultant to the Natural Resources Defense Council where he began working in 1973. Prior to retiring in 2011, he was a senior scientist and held the Wade Greene Chair for Nuclear.
Thomas B. Cochran See All
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Last Updated: Apr 27, 2023 • Article History
Table of Contents
nuclear weapon
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Apr. 26, 2023, 4:18 PM ET (AP)
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Apr. 17, 2023, 11:34 AM ET (AP)
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Top Questions
What is a nuclear weapon?
A nuclear weapon is a device designed to release energy in an explosive manner as a result of nuclear fission, nuclear fusion, or a combination of the two processes.
Are there treaties to control the proliferation of nuclear weapons?
Concerns about the devastating effects of nuclear weapons have driven governments to negotiate arms control agreements. Some of the earliest ones include the Nuclear Test-Ban Treaty of 1963 and the Treaty on the Non-proliferation of Nuclear Weapons of 1968.
When was a nuclear weapon first tested?
The first test of a nuclear weapon occurred in the United States on July 16, 1945, at the Alamogordo Bombing Range in south-central New Mexico. The test was code-named Trinity.
Which country had the most nuclear weapons?
The Soviet Union had the most nuclear weapons during the Cold War. The Soviet stockpile reached a peak of about 33,000 operational warheads in 1988, with an additional 10,000 previously deployed warheads that had been retired but not dismantled. The U.S. stockpile reached its peak in 1966 with more than 32,000 nuclear warheads.
nuclear weapon, device designed to release energy in an explosive manner as a result of nuclear fission, nuclear fusion, or a combination of the two processes. Fission weapons are commonly referred to as atomic bombs. Fusion weapons are also referred to as thermonuclear bombs or, more commonly, hydrogen bombs; they are usually defined as nuclear weapons in which at least a portion of the energy is released by nuclear fusion.
Nuclear weapons produce enormous explosive energy. Their significance may best be appreciated by the coining of the words kiloton (1,000 tons) and megaton (1,000,000 tons) to describe their blast energy in equivalent weights of the conventional chemical explosive TNT. For example, the atomic bomb dropped on Hiroshima, Japan, in 1945, containing only about 64 kg (140 pounds) of highly enriched uranium, released energy equaling about 15 kilotons of chemical explosive. That blast immediately produced a strong shock wave, enormous amounts of heat, and lethal ionizing radiation. Convection currents created by the explosion drew dust and other debris into the air, creating the mushroom-shaped cloud that has since become the virtual signature of a nuclear explosion. In addition, radioactive debris was carried by winds high into the atmosphere, later to settle to Earth as radioactive fallout. The enormous toll in destruction, death, injury, and sickness produced by the explosions at Hiroshima and, three days later, at Nagasaki was on a scale never before produced by any single weapon. In the decades since 1945, even as many countries have developed nuclear weapons of far greater strength than those used against the Japanese cities, concerns about the dreadful effects of such weapons have driven governments to negotiate arms control agreements such as the Nuclear Test-Ban Treaty of 1963 and the Treaty on the Non-proliferation of Nuclear Weapons of 1968. Among military strategists and planners, the very presence of these weapons of unparalleled destructive power has created a distinct discipline, with its own internal logic and set of doctrines, known as nuclear strategy.
The first nuclear weapons were bombs delivered by aircraft. Later, warheads were developed for strategic ballistic missiles, which have become by far the most important nuclear weapons. Smaller tactical nuclear weapons have also been developed, including ones for artillery projectiles, land mines, antisubmarine depth charges, torpedoes, and shorter-range ballistic and cruise missiles.
By far the greatest force driving the development of nuclear weapons after World War II (though not by any means the only force) was the Cold War confrontation that pitted the United States and its allies against the Soviet Union and its satellite states. During this period, which lasted roughly from 1945 to 1991, the American stockpile of nuclear weapons reached its peak in 1966, with more than 32,000 warheads of 30 different types. During the 1990s, following the dissolution of the Soviet Union and the end of the Cold War, many types of tactical and strategic weapons were retired and dismantled to comply with arms control negotiations, such as the Strategic Arms Reduction Talks, or as unilateral initiatives. By 2010 the United States had approximately 9,400 warheads of nine types, including two types of bombs, three types for intercontinental ballistic missiles (ICBMs), two types for submarine-launched ballistic missiles (SLBMs), and two types for cruise missiles. Some types existed in several modifications. Of these 9,400 warheads, an estimated 2,468 were operational (that is, mated to a delivery system such as a missile); the rest were either spares held in reserve or retired warheads scheduled to be dismantled. Of the 2,468 operational warheads, approximately 1,968 were deployed on strategic (long-range) delivery systems, and some 500 were deployed on nonstrategic (short-range) systems. Of the 500 nonstrategic warheads in the U.S. arsenal, about 200 were deployed in Europe.
The Soviet nuclear stockpile reached its peak of about 33,000 operational warheads in 1988, with an additional 10,000 previously deployed warheads that had been retired but had not been taken apart. After the disintegration of the Soviet Union, Russia accelerated its warhead dismantlement program, but the status of many of the 12,000 warheads estimated to remain in its stockpile in 2010 was unclear. Given limited Russian resources and lack of legitimate military missions, only about 4,600 of these 12,000 warheads were serviceable and maintained enough to be deployed. Of the 4,600 operational warheads, some 2,600 were deployed on strategic systems and some 2,000 on nonstrategic systems. A global security concern is the safety of Russia’s intact warheads and the security of nuclear materials removed from dismantled warheads.
Beginning in the 1990s, the arsenals of the United Kingdom, France, and China also underwent significant change and consolidation. Britain eliminated its land-based army, tactical naval, and air nuclear missions, so that its arsenal, which contained some 350 warheads in the 1970s, had just 225 warheads in 2010. Of these, fewer than 160 were operational, all on its ballistic missile submarine fleet. Meanwhile, France reduced its arsenal from some 540 operational warheads at the end of the Cold War to about 300 in 2010, eliminating several types of nuclear weapon systems. The Chinese stockpile remained fairly steady during the 1990s and then started to grow at the beginning of the 21st century. By 2010 China had about 240 warheads in its stockpile, some 180 of them operational and the rest in reserve or retirement.
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Israel maintained an undeclared nuclear stockpile of 60 to 80 warheads, but any developments were kept highly secret. India was estimated to have 60 to 80 assembled warheads and Pakistan about 70 to 90. Most of India’s and Pakistan’s warheads were thought not to be operational, though both countries—rivals in the incipient arms race on the Indian subcontinent—were thought to be increasing their stockpiles. North Korea, which joined the nuclear club in 2006, may have produced enough plutonium by 2010 for as many as 8 to 12 warheads, though it was not clear that any of these was operational.
Trinity Site
On July 16, 1945, one week after the establishment of White Sands Missile Range (WSMR), the world’s first atomic bomb was detonated in the north-central portion of the missile range, approximately 60 miles north of White Sands National Monument.
For the Project Trinity test, the bomb was placed atop a 100-foot steel tower that was designated Zero. Ground Zero was at the foot of the tower. Equipment, instruments, and observation points were established at varying distances from Ground Zero. The wooden observation shelters were protected by concrete and earthen barricades, and the nearest observation point was 5.7 miles from Ground Zero.
At 5:30 a.m. on July 16, the nuclear device, known as “Gadget,” was successfully detonated. To most observers—watching through dark glasses—the brilliance of the light from the explosion overshadowed the shock wave and sound that arrived some seconds later. A multi-colored cloud surged 38,000 feet into the air within seven minutes. Where the tower had been was a crater one-half mile across and eight feet deep. Sand in the crater was fused by the intense heat into a glass-like solid, the color of green jade. This material was given the name trinitite. The explosion point was named Trinity Site.
Although no information on the test was released until after the atomic bomb had been used as a weapon, the flash of light and shock wave made a vivid impression over an area with a radius of at least 160 miles.
The world’s second atomic bomb, codenamed “Little Boy,” was exploded over Hiroshima, Japan, on August 6, 1945. Three days later, a third bomb codenamed “Fat Man,” devastated the city of Nagasaki. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. The bombs exploded at Trinity Site and Nagasaki had plutonium cores. A “Fat Man” bomb casing is on display in front of the WSMR visitor center.
After the explosion, Trinity Site was encircled with more than a mile of chain-link fencing, and signs were posted to warn people of radioactivity. The site was closed to both WSMR personnel and the general public. By 1953, much of the radioactivity had subsided, and the first Trinity Site open house was held in September of that year.
In 1965, Army officials erected a monument on Ground Zero. In 1975, the National Park Service designated Trinity Site as a National Historic Landmark. The landmark includes base camp, where the scientists and support group lived; the McDonald ranch house, where the plutonium core was assembled; as well as Ground Zero.
Today, visits to the site are sponsored by WSMR in April and October. The rest of the year the site is closed to the public because it lies within the impact zone for missiles fired into the northern part of WSMR.
For more information on Trinity Site see the White Sands Missile Range Public Affairs website.
AI Is Like … Nuclear Weapons?
The concern, as Edward Teller saw it, was quite literally the end of the world. He had run the calculations, and there was a real possibility, he told his Manhattan Project colleagues in 1942, that when they detonated the world’s first nuclear bomb, the blast would set off a chain reaction. The atmosphere would ignite. All life on Earth would be incinerated. Some of Teller’s colleagues dismissed the idea, but others didn’t. If there were even a slight possibility of atmospheric ignition, said Arthur Compton, the director of a Manhattan Project lab in Chicago, all work on the bomb should halt. “Better to accept the slavery of the Nazi,” he later wrote, “than to run a chance of drawing the final curtain on mankind.”
I offer this story as an analogy for—or perhaps a contrast to—our present AI moment. In just a few months, the novelty of ChatGPT has given way to utter mania. Suddenly, AI is everywhere. Is this the beginning of a new misinformation crisis? A new intellectual-property crisis? The end of the college essay? Of white-collar work? Some worry, as Compton did 80 years ago, for the very future of humanity, and have advocated pausing or slowing down AI development; others say it’s already too late.
In the face of such excitement and uncertainty and fear, the best one can do is try to find a good analogy—some way to make this unfamiliar new technology a little more familiar. AI is fire. AI is steroids. AI is an alien toddler. (When I asked for an analogy of its own, GPT-4 suggested Pandora’s box—not terribly reassuring.) Some of these analogies are, to put it mildly, better than others. A few of them are even useful.
Given the past three years, it’s no wonder that pandemic-related analogies abound. AI development has been compared to gain-of-function research, for example. Proponents of the latter work, in which potentially deadly viruses are enhanced in a controlled laboratory setting, say it’s essential to stopping the next pandemic. Opponents say it’s less likely to prevent a catastrophe than to cause one—whether via an accidental leak or an act of bioterrorism.
At a literal level, this analogy works pretty well. AI development really is a kind of gain-of-function research—except algorithms, not viruses, are the things gaining the functions. Also, both hold out the promise of near-term benefits: This experiment could help to prevent the next pandemic; this AI could help to cure your cancer. And both come with potential, world-upending risks: This experiment could help to cause a pandemic many times deadlier than the one we just endured; this AI could wipe out humanity entirely. Putting a number to the probabilities for any of these outcomes, whether good or bad, is no simple thing. Serious people disagree vehemently about their likelihood.
What the gain-of-function analogy fails to capture are the motivations and incentives driving AI development. Experimental virology is an academic undertaking, mostly carried out at university laboratories by university professors, with the goal at least of protecting people. It is not a lucrative enterprise. Neither the scientists nor the institutions they represent are in it to get rich. The same cannot be said when it comes to AI. Two private companies with billion-dollar profits, Microsoft (partnered with OpenAI) and Google (partnered with Anthropic), are locked in a battle for AI supremacy. Even the smaller players in the industry are flooded with cash. Earlier this year, four top AI researchers at Google quit to start their own company, though they weren’t exactly sure what it would do; about a week later, it had a $100 million valuation. In this respect, the better analogy is …
Social media. Two decades ago, there was fresh money—lots of it—to be made in tech, and the way to make it was not by slowing down or waiting around or dithering about such trifles as the fate of democracy. Private companies moved fast at the risk of breaking human civilization, to hell with the haters. Regulations did not keep pace. All of the same could be said about today’s AI.
The trouble with the social-media comparison is that it undersells the sheer destructive potential of AI. As damaging as social media has been, it does not present an existential threat. Nor does it appear to have conferred, on any country, very meaningful strategic advantages over foreign adversaries, worries about TikTok notwithstanding. The same cannot be said of AI. In that respect, the better analogy is …
Nuclear weapons. This comparison captures both the gravity of the threat and where that threat is likely to originate. Few individuals could muster the colossal resources and technical expertise needed to construct and deploy a nuclear bomb. Thankfully, nukes are the domain of nation-states. AI research has similarly high barriers to entry and similar global geopolitical dynamics. The AI arms race between the U.S. and China is under way, and tech executives are already invoking it as a justification for moving as quickly as possible. As was the case for nuclear-weapons research, citing international competition has been a way of dismissing pleas to pump the brakes.
But nuclear-weapons technology is much narrower in scope than AI. The utility of nukes is purely military; and governments, not companies or individuals, build and wield them. That makes their dangers less diffuse than those that come from AI research. In that respect, the better analogy is …
Electricity. A saw is for cutting, a pen for writing, a hammer for pounding nails. These things are tools; each has a specific function. Electricity does not. It’s less a tool than a force, more a coefficient than a constant, pervading virtually all aspects of life. AI is like this too—or it could be.
Except that electricity never (really) threatened to kill us all. AI may be diffuse, but it’s also menacing. Not even the nuclear analogy quite captures the nature of the threat. Forget the Cold War–era fears of American and Soviet leaders with their fingers hovering above little red buttons. The biggest threat of superintelligent AI is not that our adversaries will use it against us. It’s the superintelligent AI itself. In that respect, the better analogy is …
Teller’s fear of atmospheric ignition. Once you detonate the bomb—once you build the superintelligent AI—there is no going back. Either the atmosphere ignites or it doesn’t. No do-overs. In the end, Teller’s worry turned out to be unfounded. Further calculations demonstrated that the atmosphere would not ignite—though two Japanese cities eventually did—and the Manhattan Project moved forward.
No further calculations will rule out the possibility of AI apocalypse. The Teller analogy, like all the others, only goes so far. To some extent, this is just the nature of analogies: They are illuminating but incomplete. But it also speaks to the sweeping nature of AI. It encompasses elements of gain-of-function research, social media, and nuclear weapons. It is like all of them—and, in that way, like none of them.
