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