The first atomic bomb was detonated on July 16, 1945, in the Jornada del Muerto desert of New Mexico, at a spot named Trinity Site. That single test launched a nuclear testing era that would span decades and stretch across deserts, remote Pacific atolls, and vast stretches of Central Asia. The United States alone conducted over 1,000 tests at multiple locations, and other nuclear powers established their own proving grounds on nearly every continent.
Trinity Site: Where It All Started
Manhattan Project scientists detonated the first atomic device, known as “the Gadget,” at 5:29 a.m. on July 16, 1945, at the Trinity Site near Alamogordo, New Mexico. The location was chosen for its remoteness: the Jornada del Muerto (Spanish for “Journey of the Dead Man”) is a flat, sparsely populated stretch of desert within what is now White Sands Missile Range. The blast vaporized the steel tower holding the bomb and fused the surrounding sand into a glassy, mildly radioactive mineral later called trinitite.
Today, the Trinity Site is a National Historic Landmark. The U.S. Army opens it to the public twice a year, on the first Saturday in April and the third Saturday in October, free of charge. Visitors need a government-issued photo ID and must enter through Stallion Gate between 8 a.m. and 2 p.m. Radiation levels at the site are now extremely low. Estimates from radiation studies found that exposures for most New Mexico residents from the original test were on the order of, or less than, what people receive annually from natural background radiation.
The Nevada Test Site
After Trinity, the U.S. needed a permanent, domestic proving ground. In 1951, the government established the Nevada Test Site (now the Nevada National Security Site) about 65 miles northwest of Las Vegas. This sprawling desert complex, covering roughly 1,360 square miles, became the primary location for American nuclear weapons testing for the next four decades.
A total of 100 atmospheric tests were conducted there through July 1962, when the U.S. shifted to underground detonations following growing public concern about radioactive fallout. The first fully contained underground nuclear explosion, called Rainier, had already taken place on September 19, 1957, inside a tunnel beneath a high mesa in the site’s northwest corner. That test confirmed underground detonation was feasible and could eliminate fallout and other offsite effects. After the atmospheric testing era ended, the U.S. went on to conduct 828 underground tests at the Nevada site.
The atmospheric tests at Nevada had serious health consequences for communities downwind. Radioactive fallout drifted across parts of Nevada, Utah, Arizona, Idaho, and New Mexico, exposing rural populations to elevated radiation. The U.S. government later acknowledged this harm through the Radiation Exposure Compensation Act, which identified affected counties across those states and provided payments to residents who developed certain cancers after living in downwind areas during the testing period.
The Pacific Proving Grounds
Some weapons were too powerful to test on the U.S. mainland. Between 1946 and 1958, the United States conducted 66 nuclear tests in or near the Marshall Islands, a chain of coral atolls in the central Pacific Ocean. The two primary sites were Bikini Atoll (23 tests) and Enewetak Atoll (42 tests), with one additional test at a nearby open-ocean location.
The Pacific tests included the largest and most destructive American detonations. The most consequential was Castle Bravo, a thermonuclear (hydrogen bomb) test conducted at Bikini Atoll on March 1, 1954. Bravo yielded 15 megatons, roughly 1,000 times the power of the Hiroshima bomb, and it performed far beyond expectations. An unexpected wind shear carried heavy fallout east over inhabited atolls, delivering high radiation doses to island populations. The 1954 Castle series of tests accounted for most of the total fallout deposited across the Marshall Islands.
The people of Bikini Atoll were relocated before testing began in 1946 and have never permanently returned. Decades later, residual contamination in the soil remains a concern on several atolls, particularly from long-lived radioactive elements like cesium-137.
Soviet Testing in Kazakhstan
The Soviet Union’s primary nuclear testing ground was the Semipalatinsk Test Site in northeastern Kazakhstan, a vast area of steppe roughly the size of Wales. Between 1949 and 1962, the Soviets conducted atmospheric tests there, resulting in widespread radioactive contamination of the surrounding region. Settlements east of the test site, in what is now Abai oblast, were the most heavily contaminated.
Unlike the relatively evacuated American test zones, Semipalatinsk was surrounded by populated villages. Residents of communities like Barshatas and Ayagoz received measurable radiation doses from individual tests, and cumulative exposure over years of testing left a lasting health legacy. Kazakhstan closed the site in 1991 after independence from the Soviet Union, and it remains one of the most studied examples of nuclear contamination affecting a civilian population.
French Tests in Algeria and Polynesia
France conducted its nuclear testing program across two distinct locations, both in colonial or overseas territories. Between 1960 and 1966, the French military carried out 17 nuclear tests in the Algerian Sahara, near the towns of Reggane and In Ekker. Four were atmospheric detonations near Reggane, and 13 were underground tests in the Hoggar Massif near In Ekker.
After Algeria gained independence in 1962, France relocated its testing program to French Polynesia in the South Pacific, where it continued conducting atmospheric and underground tests until 1996. The choice of remote colonial territories for these tests has drawn lasting criticism, particularly from affected populations in both Algeria and Polynesia who have sought recognition and compensation for health effects linked to fallout exposure.
British Tests in Australia
The United Kingdom tested its nuclear weapons in Australia during the 1950s and early 1960s, using sites at Maralinga and Emu Field in the South Australian outback, as well as the Montebello Islands off the Western Australian coast. These tests helped Britain establish itself as a nuclear power but left behind contaminated land that required extensive cleanup efforts continuing into the 1990s. Indigenous Australian communities, whose traditional lands overlapped with test areas, were among those most affected.
A Global Footprint
In total, nuclear weapons were tested on every continent except South America and Antarctica. The United States used sites in New Mexico, Nevada, the Pacific, Alaska (Amchitka Island), Colorado, and Mississippi. The Soviet Union tested primarily in Kazakhstan but also at Novaya Zemlya, an Arctic archipelago where the 50-megaton Tsar Bomba was detonated in 1961. China conducted its tests at Lop Nur in the Xinjiang desert. India and Pakistan each tested underground devices in their own territories during the 1990s, and North Korea has conducted underground tests at Punggye-ri since 2006.
The shift from atmospheric to underground testing, formalized by the 1963 Partial Test Ban Treaty, dramatically reduced global fallout but did not eliminate local contamination. Many former test sites remain restricted or require ongoing environmental monitoring. The landscapes chosen for nuclear testing shared common traits: they were remote, arid, and often home to indigenous or marginalized populations who bore the greatest health and environmental costs.