The United States holds the second-largest arsenal of nuclear weapons (after the Russian Federation) among the nine nuclear-armed countries. Under the Manhattan Project, the United States became the first country to manufacture nuclear weapons and remains the only country to have used them in combat, with the bombings of Hiroshima and Nagasaki in World War II against Japan. In total it has conducted 1,054 known nuclear explosive tests, the most of any country. It is an original party to and one of the five "nuclear-weapon states" recognized by the 1968 Treaty on the Non-Proliferation of Nuclear Weapons.

, the US and Russia possess a comparable number of warheads; together more than 90% of the world's stockpile. The US holds in total 5,177 warheads, of which 3,700 are stockpiled, and 1,477 are awaiting dismantlement. Of the stockpile, 1,770 are deployed, while 1,930 are held in reserve. The president of the United States has the sole authority to use nuclear weapons. US policy permits nuclear first use and launch on warning, and aims to "deter Russia, the PRC, and the DPRK simultaneously".

The US stockpile is mostly under Strategic Command, assigned to its nuclear triad: 1,920 to 280 Trident II submarine-launched ballistic missiles aboard 14 Ohio-class submarines, 800 to 400 silo-based Minuteman III intercontinental ballistic missiles, and 780 B61 and B83 bombs and AGM-86B cruise missiles to 19 B-2 Spirit and 46 B-52 Stratofortress bombers respectively. The US plans to modernize its triad with the Columbia-class submarine, Sentinel ICBM, and B-21 Raider, from 2029. Early warning is provided by radars including Solid State Phased Arrays and satellites including the Space-Based Infrared System. The Missile Defense Agency coordinates the US anti-ballistic missile network: the Ground-Based Interceptor, Aegis, Terminal High Altitude Area Defense, and MIM-104 Patriot systems.

Additionally, 200 B61 nuclear bombs are available for tactical nuclear use by fighter aircraft. The US stations approximately 100 of these in six European NATO countries: Belgium, Germany, Italy, the Netherlands, Turkey, and United Kingdom. The US extends a nuclear umbrella to all NATO countries, and also South Korea, Japan, and Australia. Since the 2014 Russian annexation of Crimea, the US has more frequently moved strategic nuclear delivery systems to the territory of its allies, with Bomber Task Force deployments in Australia, Qatar, Romania, and South Korea, while Ohio-class submarines have docked in Scotland and South Korea.

Throughout the Cold War, the United States and the Soviet Union competed in the nuclear arms race. From 1951, the US became the first country to develop thermonuclear weapons. From the 1950s, the US stationed nuclear weapons in at least 17 other nations, including NATO allies, South Korea, Japan, Taiwan, and the Philippines, while Strategic Air Command operated hundreds of strategic bombers, under the policies of massive retaliation and containment of Eastern Bloc countries. By the 1960s, ICBMs were deployed in silos, such as the Atlas and Titan, and aboard submarines as Polaris, with the arsenal peaking at 31,000 warheads in 1967. The 1962 Cuban Missile Crisis is regarded as a nuclear close call that cemented the concept of mutually assured destruction. Technologies advanced in the 1980s, with the Peacekeeper ICBM and proposed space-based Strategic Defense Initiative missile defense system. When the Cold War ended, all Army and surface Navy nuclear weapons were withdrawn, and Strategic Air Command was superseded by Strategic Command. The arsenal was also limited by bilateral treaties, beginning with START I. Its successor, New START, expired in 2026. Since 2025, the US has pursued the space-based Golden Dome missile defense system.

Between 1940 and 1996, the US spent over US$ in present-day terms on nuclear weapons infrastructure, and nuclear forces maintenance is projected to cost $60 billion per year from 2021 through 2030. The US produced over 70,000 nuclear warheads, more than all other states combined. Design takes place at Los Alamos, Livermore, and Sandia laboratories; tests were conducted at Nevada Test Site and Pacific Proving Grounds. Until the 1963 Partial Nuclear Test Ban Treaty, the vast majority of tests were atmospheric. Subsequent underground testing limited nuclear fallout. Nuclear sites radioactively contaminated civilian communities: the US government compensated Marshall Islanders over US$759 million for testing exposure, – updated regularly and US citizens over US$2.5 billion. The US began a testing moratorium in 1992U.S. Nuclear Weapons Tests, Congressional Research Service, January 23, 2025 and signed the Comprehensive Nuclear-Test-Ban Treaty in 1996, but has not ratified it. Stockpile stewardship is the current warhead maintenance program, using experiments including supercomputer simulation and inertial confinement fusion.

Development history

Manhattan Project

The United States first began developing nuclear weapons during World War II under the order of President Franklin Roosevelt in 1939, motivated by the fear that they were engaged in a race with Nazi Germany to develop such a weapon. After a slow start under the direction of the National Bureau of Standards, at the urging of British scientists and American administrators, the program was put under the Office of Scientific Research and Development, and in 1942 it was officially transferred under the auspices of the United States Army and became known as the Manhattan Project, an American, British and Canadian joint venture. Under the direction of General Leslie Groves, over thirty different sites were constructed for the research, production, and testing of components related to bomb-making. These included the Los Alamos National Laboratory at Los Alamos, New Mexico, under the direction of physicist Robert Oppenheimer, the Hanford plutonium production facility in Washington, and the Y-12 National Security Complex in Tennessee.

By investing heavily in breeding plutonium in early nuclear reactors and in the electromagnetic and gaseous diffusion enrichment processes for the production of uranium-235, the United States was able to develop three usable weapons by mid-1945. The Trinity test was a plutonium implosion-design weapon tested on 16 July 1945, with around a 20 kiloton yield.

Faced with a planned invasion of the Japanese home islands scheduled to begin on 1 November 1945 and with Japan not surrendering, President Harry S. Truman ordered the atomic raids on Japan. On 6 August 1945, the US detonated a uranium-gun design bomb, Little Boy, over the Japanese city of Hiroshima with an energy of about 15 kilotons of TNT, killing approximately 70,000 people, among them 20,000 Japanese combatants and 20,000 Korean forced laborers, and destroying nearly 50,000 buildings (including the 2nd General Army and Fifth Division headquarters). Three days later, on 9 August, the US attacked Nagasaki using a plutonium implosion-design bomb, Fat Man, with the explosion equivalent to about 20 kilotons of TNT, destroying 60% of the city and killing approximately 35,000 people, among them 23,200–28,200 Japanese munitions workers, 2,000 Korean forced laborers, and 150 Japanese combatants.

On 1 January 1947, the Atomic Energy Act of 1946 (known as the McMahon Act) took effect, establishing the United States Atomic Energy Commission (AEC) as a civilian agency to take over control of nuclear activities from the Manhattan Project. On 15 August 1947, the Manhattan Project was formally ended.

During the Cold War

The American atomic stockpile was small and grew slowly in the immediate aftermath of World War II, and the size of that stockpile was a closely guarded secret.Young and Schilling, Super Bomb, pp. 156–157. However, there were forces that pushed the United States towards greatly increasing the size of the stockpile. Some of these were international in origin and focused on the increasing tensions of the Cold War, including the loss of China, the Soviet Union becoming an atomic power, and the onset of the Korean War.Schwartz, "Introduction", in Atomic Audit, pp. 12–13. And some of the forces were domestic – both the Truman administration and the Eisenhower administration wanted to rein in military spending and avoid budget deficits and inflation.Schwartz, "Introduction", in Atomic Audit, pp. 13–14. It was the perception that nuclear weapons gave more "bang for the buck" and thus were the most cost-efficient way to respond to the security threat the Soviet Union represented.Schwartz, "Introduction", in Atomic Audit, pp. 18–21.

As a result, beginning in 1950 the AEC embarked on a massive expansion of its production facilities, an effort that would eventually be one of the largest US government construction projects ever to take place outside of wartime.Young and Schilling, Super Bomb, pp. 69–70. And this production would soon include the far more powerful hydrogen bomb, which the United States had decided to move forward with after an intense debate during 1949–50.Young and Schilling, Super Bomb, pp. 1–2. as well as much smaller tactical atomic weapons for battlefield use.Schwartz, "Introduction", in Atomic Audit, p. 13.

By 1990, the United States had produced more than 70,000 nuclear warheads, in over 65 different varieties, ranging in yield from around .01 kilotons (such as the man-portable Davy Crockett shell) to the 25 megaton B41 bomb. Between 1940 and 1996, the US spent at least $ in present-day terms on nuclear weapons development. Over half was spent on building delivery mechanisms for the weapon. $ in present-day terms was spent on nuclear waste management and environmental remediation.

Richland, Washington, was the first city established to support plutonium production at the nearby Hanford nuclear site, to power the American nuclear weapons arsenals. It produced plutonium for use in cold war atomic bombs.

Throughout the Cold War, the US and USSR threatened with all-out nuclear attack in case of war, regardless of whether it was a conventional or a nuclear clash.Stone, Oliver and Kuznick, Peter, "The Untold History of the United States," (Gallery Books, 2012), pages 280–281 US nuclear doctrine called for mutually assured destruction (MAD), which entailed a massive nuclear attack against strategic targets and major populations centers of the Soviet Union and its allies. The term "mutual assured destruction" was coined in 1962 by American strategist Donald Brennan. MAD was implemented by deploying nuclear weapons simultaneously on three different types of weapons platforms.

Post–Cold War