| The first nuclear test was conducted by the | | | | 1963. Above are the per capita thyroid doses (in |
| United States on July 16, 1945, during the | | | | rads) in the continental United States resulting |
| Manhattan Project, and given the codename | | | | from all exposure routes from all atmospheric |
| "Trinity". The test was originally to confirm that | | | | nuclear tests conducted at the Nevada Test Site |
| the implosion-type nuclear weapon design was | | | | from 1951-1962. |
| feasible, and to give the scientists and military | | | | Bravo was the worst U.S. nuclear accident, but |
| officers an idea of what the actual size and | | | | many of its component problems — |
| effects of a nuclear explosion would be before | | | | unpredictably large yields, changing weather |
| they were used in combat against Japan. While | | | | patterns, unexpected fallout contamination of |
| the test gave a good approximation of many of | | | | populations and the food supply — |
| the explosion's effects, it did not give an | | | | occurred during other atmospheric nuclear |
| appreciable understanding of nuclear fallout, which | | | | weapons tests by other countries as well. |
| was not well understood by the project scientists | | | | Concerns over worldwide fallout rates eventually |
| until well after the atomic bombings of Hiroshima | | | | lead to the Partial Test Ban Treaty in 1963, which |
| and Nagasaki. | | | | limited signatories to only underground testing. Not |
| The United States conducted only six nuclear | | | | all atmospheric tests stopped, however, but |
| tests before the Soviet Union developed their | | | | because the United States and the Soviet Union in |
| first atomic bomb (Joe 1) and tested it on August | | | | particular stopped testing aboveground it cut the |
| 29, 1949. Neither country had very many nuclear | | | | number of atmospheric tests down substantially, |
| weapons to spare at first, and so testing was | | | | since around 86% of all nuclear tests were |
| relatively limited (when the U.S. used two | | | | conducted by those two countries. France |
| weapons for Operation Crossroads in 1946, they | | | | continued atmospheric testing until 1974, and |
| were detonating over 20% of their current | | | | People's Republic of China until 1980. |
| arsenal). However, by the 1950s the United | | | | Almost all new nuclear powers have announced |
| States had established a dedicated test site on its | | | | their possession of nuclear weapons with a |
| own territory (Nevada Test Site) and were also | | | | nuclear test. The only acknowledged nuclear |
| using a site in the Marshall Islands (Pacific Proving | | | | power which claims to have never conducted a |
| Grounds) for extensive nuclear testing. | | | | test was South Africa (see Vela Incident), which |
| The early tests were used primarily to discern | | | | has since claimed to have dismantled all of its |
| the military effects of nuclear weapons | | | | weapons. The state of Israel is widely thought by |
| (Crossroads had involved the effect of nuclear | | | | intelligence agencies to possess a sizeable nuclear |
| weapons on a navy, and how they functioned | | | | arsenal, though it has never tested. Experts |
| underwater) and to test new weapon designs. | | | | disagree on whether states can have reliable |
| During the 1950s these included new hydrogen | | | | nuclear arsenals — especially ones using |
| bomb designs, which were tested in the Pacific, | | | | advanced warhead designs, such as hydrogen |
| and also new and improved fission weapon | | | | bombs and miniaturized weapons — |
| designs. The Soviet Union also began testing on a | | | | without testing, though all agree that it is very |
| limited scale, primarily in Kazakhstan. During the | | | | unlikely to develop significant nuclear innovations |
| later phases of the Cold War, though, both | | | | without testing. One other approach is to use |
| countries developed accelerated testing programs, | | | | supercomputers to conduct "virtual" testing, but |
| testing many hundreds of bombs over the last | | | | the value of these simulations without actual test |
| half of the twentieth century. | | | | result data is thought to be slim. |
| Nuclear tests can involve many hazards. A | | | | Some nuclear testing has been for "peaceful" |
| number of these were best illustrated in the U.S. | | | | purposes. These so-called peaceful nuclear |
| Castle Bravo test in 1954. The weapon design | | | | explosions were used to evaluate whether nuclear |
| tested was a new form of hydrogen bomb, and | | | | explosions could be used for non-military purposes |
| the scientists underestimated how vigorously | | | | such as digging canals and artificial harbors, or to |
| some of the weapon materials would react. As a | | | | stimulate oil and gas fields. In most cases the |
| result, the explosion — with a yield of | | | | results were too radioactive for use, and the |
| 15 Mt — was over twice what was | | | | programs proved neither economically sound or |
| predicted. Aside from this problem, the weapon | | | | politically favorable. |
| also generated a large amount of radioactive | | | | Nuclear testing has also been used for clearly |
| nuclear fallout, more than had been anticipated, | | | | political purposes. The most explicit example of |
| and a change in the weather pattern caused the | | | | this was the detonation of the largest nuclear |
| fallout to be spread in a direction which had not | | | | bomb ever created, the 50 megaton Tsar Bomba |
| been cleared ahead of time. The fallout plume | | | | (with a maximum yield of 150 Mt), by the Soviet |
| spread high levels of radiation for over a hundred | | | | Union in 1961. This weapon was too large to be |
| miles, contaminating a number of populated islands | | | | practically used against an enemy target, and it is |
| in nearby atoll formations (though they were soon | | | | not thought that any were actually manufactured |
| evacuated, many of the islands' inhabitants | | | | except the one which was detonated in the test. |
| suffered from radiation burns and later from | | | | The weapon was used by the USSR as a show |
| other effects such as increased cancer rate and | | | | of Soviet strength and force, rather than to be |
| birth defects), as well as a Japanese fishing boat | | | | developed as an actual weapon or for specifically |
| (Daigo Fukuryu Maru). One member of the boat's | | | | scientific purposes. |
| crew died from radiation sickness after returning | | | | There have been many attempts to limit the |
| to port, and it was feared that the radioactive | | | | number and size of nuclear testing; the most |
| fish they had been carrying had made it into the | | | | far-reaching was the Comprehensive Test Ban |
| Japanese food supply. | | | | Treaty of 1996, which was not ratified by the |
| Because of concerns about worldwide fallout | | | | United States. Nuclear testing has since become a |
| levels, the Partial Test Ban Treaty was signed in | | | | controversial issue in the United States, with a |
| 1963. Above are the per capita thyroid doses (in | | | | number of politicians saying that future testing |
| rads) in the continental United States resulting | | | | might be necessary to maintain the aging |
| from all exposure routes from all atmospheric | | | | warheads from the Cold War. Because nuclear |
| nuclear tests conducted at the Nevada Test Site | | | | testing is seen as furthering nuclear arms |
| from 1951-1962. | | | | development, many are also opposed to future |
| Because of concerns about worldwide fallout | | | | testing as an acceleration of the arms race. |
| levels, the Partial Test Ban Treaty was signed in | | | | |