United States and weapons of mass destruction

The nuclear weapons of the United States comprise the second-largest arsenal in the world, behind Russia. The US is only country to have used nuclear weapons in warfare, in the atomic bombings of Hiroshima and Nagasaki at the end of World War II. The Manhattan Project, begun in 1942, made the US the first nuclear-armed country. The US operates a nuclear triad. The US previously possessed chemical and biological weapons. It is a ratifier of the nuclear Non-Proliferation Treaty, Biological Weapons Convention, and Chemical Weapons Convention.

As of 2025, the United States actively deploys approximately 1,770 warheads, mostly under Strategic Command, to its nuclear triad. Of these, 970 warheads on Trident II submarine-launched ballistic missiles aboard to Ohio-class submarines, with 400 warheads to silo-based Minuteman III intercontinental ballistic missiles, and 300 bombs and cruise missiles to B-2 Spirit and B-52 Stratofortress bombers. The US also forward deploys nuclear weapons in the form of approximately 100 B61 bombs in six European NATO countries: Belgium, Germany, Italy, the Netherlands, Turkey, and United Kingdom. The US warhead inventory totals 5,177 warheads, with 1,930 warheads for reserve use, and another 1,477 awaiting dismantlement.

The US carried out the first nuclear test, Trinity, three weeks prior to the atomic bombings. The Cold War's nuclear arms race began; in 1949 the Soviet Union carried out its first nuclear test, prompting the US to develop and test the first thermonuclear weapon, Ivy Mike. From the 1950s, the US stationed nuclear weapons overseas in Europe and East Asia. The 1962 Cuban Missile Crisis is regarded as a close call with World War III.

The US carried out 1,054 nuclear tests from 1945 to 1992, primarily at the Nevada Test Site and Pacific Proving Grounds. It signed the Comprehensive Nuclear-Test-Ban Treaty in 1996.

The US chemical weapons program began during World War I, and during the Cold War stockpiled primarily sarin, VX, and mustard gas. These were deployed abroad, including in Okinawa and West Germany, and withdrawn in 1971 and in 1990 respectively. Under the Central Intelligence Agency's MKUltra, psychochemical warfare was also investigated, weaponizing the BZ incapacitating agent. The US committed to destroying its chemical weapons arsenal in 1991, which was accomplished by 2023 at a total cost of US$40 billion.

The US biological weapons program ran from 1943 to 1969. It weaponized and stockpiled the biological agents that cause anthrax, botulism, brucellosis, Q-fever, toxic shock syndrome, and Venezuelan equine encephalitis virus. In 1969 the program was renounced, alongside the first use of chemical weapons.