A nuclear weapon is an explosive device that derives its destructive force from nuclear fission, nuclear fusion, or a combination of the two. Nuclear weapons are alternately called atom bombs, atomic bombs, A-bombs, nuclear bombs, nuclear warheads, or simply nukes. All nuclear weapons fit into one of two broad categories: fission and combination weapons, or the even-more-destructive fusion-based designs, which are technically thermonuclear weapons and may also be referred to as thermonuclear bombs, fusion weapons, hydrogen bombs, or H-bombs. Nuclear weapons unleash enormous amounts of explosive force, which is measured in kilotons (1,000 tons of TNT) and megatons (1,000,000 tons of TNT), as well as heat and radiation. They are easily the most fearsome weapons on Earth, capable of producing more death, destruction, injury, and sickness than any other weapon.
Nuclear weapon stockpiles today
It is estimated that there are approximately 13,080 nuclear warheads in the world today. While this is far fewer than either the U.S. or Russia possessed during their Cold War peak, it is notable that there are more countries with nuclear weapons than there were 30-40 years ago. At present, Russia maintains the highest number of nuclear weapons, with an estimated 6,257 total warheads. Of these, 1,458 are actively deployed (current START II treaty limits both the U.S. and Russia to 1550 deployed total), 3039 are inactive but available to be made active, and 1,760 are retired and awaiting dismantling. The United States follows closely behind with 5,550 total nuclear weapons: 1,389 active, 2,361 inactive but available, and 1,800 in line to be dismantled.
Which Countries Have Nuclear Weapons?
Country | Total Weapons | Actively Deployed |
|---|---|---|
| Russia | 6,257 | 1,458 |
| United States | 5,550 | 1,389 |
| China | 350 | 0 |
| France | 290 | 0 |
| United Kingdom | 225 | 0 |
| Pakistan | 165 | 0 |
| India | 156 | 0 |
| Israel | 90 | 0 |
| North Korea | 50 | 0 |
Nuclear bombs dropped during World War II
To date, nuclear weapons have been used in war only twice. At the end of World War II, the United States dropped a nuclear bomb called Little Boy on Hiroshima, Japan, on August 6, 1945, and a second bomb called Fat Man on Nagasaki, Japan, on August 9, 1945. Little Boy detonated with an explosive force of approximately 15 kilotons, which leveled most buildings within a 1-mile radius. The shock wave was followed by a blast of heat at 6,000°C (10,830°F), which ignited or incinerated anything flammable and turned the blast zone into a firestorm. Finally, the explosion produced lethal ionizing radiation and lingering radioactive fallout, in which debris blasted into the stratosphere by the initial explosion is held aloft by atmospheric winds and settles back to Earth over the next several days. All told, the bombing of Hiroshima was estimated by a 1945 government report to have resulted in 66,000 deaths and another 69,000 injuries. Nagasaki's totals were a lesser, but still devastating 39,000 deaths and 25,000 injuries.
Nuclear escalation during the Cold War
The bombings of Hiroshima and Nagasaki established nuclear weapons as the ultimate weapons of war, which kicked off an arms race between the United States and the Soviet Union. A major component of the "Cold War," in which the U.S. and U.S.S.R. openly competed without actually declaring war on one another, the stockpiling of nuclear weapons continued into the late 1980s. According to the Bulletin of Atomic Scientists, the nuclear arms race reached its peak in 1986, by which time the Soviet Union possessed more than 40,000 nuclear warheads and the United States had 23,000 (down from more than 31,000 in 1967). Much of this proliferation was based around the idea of "mutually assured destruction," in which both sides believed that the best way to avoid nuclear war was to have so many nukes that the opponent would not launch an attack because they feared they could not destroy enough of the target country's arsenal to avoid being devastated themselves by a retaliatory attack. After the Soviet Union dissolved in 1991, thousands of nuclear weapons on both sides were dismantled.
Treaties that limit nuclear weapons
Because of the broad lethality and destructive potential of nuclear weapons, governments have negotiated arms control agreements such as the 1970 Nuclear Non-Proliferation Treaty (NPT), the 1972 Strategic Arms Limitation Treaty (SALT), and the 1991 Strategic Arms Reduction Treaty (START). The NPT’s purpose is to inhibit the spread of nuclear weapons. It designates five countries as nuclear-weapon states (NWS)—the United States, Russia, China, France, and the United Kingdom—and classifies the rest as non-nuclear weapon states (NNWS). Under the treaty, NWS agree not to help NNWS develop or obtain nuclear weapons, and NNWS agree not to attempt to develop or obtain nuclear weapons on their own. Countries of both classifications further agree to help one another develop nuclear energy for peaceful purposes (see nuclear power by country) and to negotiate nuclear disarmament in good faith. Nearly every country in the world had accepted the NPT as of 2022, though North Korea famously withdrew from the treaty in 2003.
