'' (foreground) in Hong Kong Harbor in 1967, was involved in several famous
anti-nuclear protest voyages against nuclear testing in the Pacific. (indicated in red), attached to
Kurchatov (along the
Irtysh river). The site comprised an area
the size of Wales. The first atomic weapons test was conducted near Alamogordo, New Mexico, on July 16, 1945, during the
Manhattan Project, and given the codename "
Trinity". The test was originally to confirm that the implosion-type
nuclear weapon design was feasible, and to give an idea of what the actual size and effects of a
nuclear explosion would be before it was used in combat against Japan. The test gave a good approximation of many of the explosion's effects, but did not give an appreciable understanding of
nuclear fallout, which was not well understood by the project scientists until after the
atomic bombings of Hiroshima and Nagasaki. The United States conducted six atomic tests before the Soviet Union developed its first atomic bomb (
RDS-1) and tested it on August 29, 1949. Neither country had many atomic weapons to spare at first, and testing was relatively infrequent. (When the US used two weapons for
Operation Crossroads in 1946, they were detonating over 20% of their current arsenal.) By the 1950s the United States had established a dedicated test site on its own territory (
Nevada Test Site) and was also using a site in the
Marshall Islands (
Pacific Proving Grounds) for extensive atomic and nuclear testing. The early tests were used primarily to discern the military effects of atomic weapons (
Crossroads had involved the effect of atomic weapons on a navy, and how they functioned underwater) and to test new weapon designs. During the 1950s, these included new hydrogen bomb designs, which were tested in the Pacific, and also new and improved fission weapon designs. The Soviet Union also began testing on a limited scale, primarily in
Kazakhstan. During the later phases of the
Cold War, both countries developed accelerated testing programs, testing many hundreds of bombs over the last half of the 20th century. fallout plume spread dangerous levels of radiation over an area over long, including inhabited islands. Atomic and nuclear tests can involve many hazards. Some of these were illustrated in the US
Castle Bravo test in 1954. The weapon design tested was a new form of hydrogen bomb, and the scientists underestimated how vigorously some of the weapon materials would react. As a result, the explosion, with a
yield of 15
Mt, was over twice what was predicted. The weapon also generated a large amount of radioactive
nuclear fallout, more than had been anticipated, and a change in the weather pattern caused the fallout to spread in a direction not cleared in advance. The fallout plume spread high levels of radiation for over , contaminating populated islands in nearby atoll formations. Though they were soon evacuated, many of the islands' inhabitants suffered from radiation burns and later from other effects such as increased cancer rate and birth defects, as did the crew of the Japanese fishing boat
Daigo Fukuryū Maru. One crewman died from radiation sickness after returning to port, and it was feared that the radioactive fish they had been carrying may have entered the Japanese food supply. was signed in 1963. Above are the per capita
thyroid doses (in
rads) in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the
Nevada Test Site from 1951 to 1962. Castle Bravo was the worst US nuclear accident, but many of its component problems—unpredictably large yields, changing weather patterns, unexpected fallout
contamination of populations and the food supply—also occurred during atmospheric nuclear weapons tests by other countries. Concerns over worldwide fallout rates eventually led to the
Partial Test Ban Treaty in 1963, which limited signatories to underground testing. Not all countries ceased atmospheric testing, but because the United States and the Soviet Union were responsible for roughly 86% of all nuclear tests, their compliance cut the overall level substantially. France continued atmospheric testing until 1974, and China until 1980. A tacit moratorium on testing was in effect from 1958 to 1961 and ended with a series of Soviet tests in late 1961, including the
Tsar Bomba, the largest nuclear weapon ever tested. The United States responded in 1962 with
Operation Dominic, involving dozens of tests including the explosion of a missile launched from a submarine. Almost all new nuclear powers have announced their possession of nuclear weapons with a nuclear test. The only acknowledged nuclear power that claims never to have conducted a test is South Africa (although see
Vela incident), which has since dismantled all of its weapons. Israel is widely thought to possess a sizeable nuclear arsenal though it has never tested, unless they were involved in Vela. Experts disagree on whether states can have reliable nuclear arsenals, especially ones using advanced warhead designs, such as hydrogen bombs and miniaturized weapons, without testing, although all agree that it is unlikely that significant nuclear innovations can be developed without testing. One other approach is to use
supercomputers to conduct "virtual" testing, but codes need to be validated against test data. There have been many attempts to limit the number and size of nuclear tests; the most far-reaching was the
Comprehensive Test Ban Treaty of 1996, which, , had not been ratified by eight of the "
Annex 2 countries" required for it to take effect, including the United States. Nuclear testing became a controversial issue in the United States, with a number of politicians saying that future testing might be necessary to maintain the ageing warheads from the
Cold War. Nuclear testing is seen as furthering nuclear arms development, and many are opposed to future testing as an acceleration of the arms race. In
total nuclear test megatonnage, from 1945 to 1992, 520 atmospheric nuclear explosions (including eight underwater) were conducted with a total yield of 545
megatons, with a peak occurring in 1961–1962, when 340 megatons were detonated in the atmosphere by the United States and
Soviet Union. The estimated number of underground nuclear tests conducted in the period from 1957 to 1992 was 1,352 explosions with a total yield of 90 Mt. Image: Trinity shot color.jpg|The first atomic test, "
Trinity", took place on July 16, 1945. Image: Sedan Plowshare Crater.jpg|The
Sedan test of 1962 was an experiment by the United States in using nuclear devices to excavate large amounts of earth. File:330-PS-3256 (45898 AC) (17204655228).jpg|
Kytoon balloons were used on Indian Springs Air Force Base, Nevada, April 20, 1952, to get exact weather information during atomic test periods. ==Yield==