The United States conducted the vast majority of its nuclear tests at the Nevada Test Site, about 65 miles northwest of Las Vegas. Between 1951 and 1992, 928 nuclear detonations took place there, including 100 in the open atmosphere and 828 underground. A significant number of additional tests happened in the Pacific Ocean, on remote atolls in the Marshall Islands. Since the U.S. stopped full-scale explosive testing in 1992, all nuclear weapons work has moved to laboratories and small-scale underground experiments that don’t produce a nuclear chain reaction.
The Nevada Test Site
Now called the Nevada National Security Site, this 1,360-square-mile stretch of desert north of Las Vegas was the country’s primary nuclear proving ground for four decades. The site hosted everything from small tactical weapon tests to massive underground detonations that shook the desert floor. Atmospheric tests ran from 1951 until 1963, when the Limited Test Ban Treaty pushed all testing underground. Underground tests continued until 1992, when the U.S. entered a voluntary moratorium on explosive nuclear testing that remains in effect today.
Fallout from the atmospheric tests drifted across parts of Nevada, Utah, Arizona, Idaho, and New Mexico. The federal government eventually recognized this through the Radiation Exposure Compensation Act, which covers residents of specific downwind counties in those states, including Coconino, Navajo, and Apache counties in Arizona and Nye, Lincoln, and Clark counties in Nevada, among others.
The Pacific Proving Grounds
Before Nevada became the go-to location, and alongside it during the 1950s, the U.S. tested nuclear weapons on remote atolls in the Marshall Islands. Bikini Atoll and Enewetak Atoll were the two primary sites. Between 1946 and 1958, 67 nuclear tests took place across the Marshall Islands, including the first hydrogen bomb in 1952. The cumulative explosive force of those tests equaled roughly 7,000 times the power of the Hiroshima bomb.
The local populations of both atolls were displaced before testing began. The 1954 Castle Bravo test at Bikini, the most powerful U.S. nuclear detonation ever, spread radioactive fallout far beyond the predicted zone, contaminating inhabited islands and a Japanese fishing vessel. The blast carved a crater into the atoll’s reef that is still visible today, alongside warships sunk during the 1946 tests that sit on the lagoon floor. Bikini Atoll is now a UNESCO World Heritage Site, recognized as a stark testament to the nuclear age.
Amchitka Island, Alaska
Three underground nuclear tests took place on Amchitka, a small island at the tip of Alaska’s Aleutian chain. The first, Long Shot, was an 80-kiloton detonation in 1965, drilled 710 meters into the earth. Its purpose was to help scientists develop equipment that could distinguish foreign nuclear tests from natural earthquakes.
The tests escalated quickly. Milrow, a 1.2-megaton device, followed in 1969. Then came Cannikin in 1971: a 5-megaton bomb buried nearly 1,800 meters underground, making it the largest nuclear test the United States ever conducted. The blast was 400 times more powerful than the Hiroshima bomb and generated a shock wave equivalent to a 7.0 earthquake. Witnesses reported the entire island rising and falling roughly 20 feet. The ground above the blast collapsed, forming a lake a mile wide. Cannikin drew major public opposition, and no further tests were conducted on the island.
Colorado and New Mexico: Industrial Tests
Not all U.S. nuclear tests were for weapons. Under a program called Plowshare, the government explored using nuclear explosions for industrial purposes like stimulating natural gas flow from deep rock formations. Three such tests took place: Project Gasbuggy in New Mexico, Project Rulison in Colorado, and Project Rio Blanco, also in Colorado.
Rio Blanco, the final test in 1973, involved three nuclear devices detonated nearly simultaneously at depths between 5,840 and 6,690 feet. The goal was to fracture gas-bearing sandstone and boost production. It partially worked, with one well producing about 98 million cubic feet of gas over 28 days, but the underground fractures didn’t extend as far as scientists predicted. The chimneys created by the three blasts never connected to each other. The program was abandoned, though environmental monitoring at the Rio Blanco site has continued since 1976 with no radioactive contamination detected in any samples.
How the U.S. Tests Weapons Now
The U.S. has not detonated a nuclear weapon since September 1992. Instead, it maintains its arsenal through a program called Stockpile Stewardship, which uses a combination of small-scale experiments, advanced simulations, and high-tech laboratory facilities spread across the country.
At the Nevada site, the government still conducts what are called subcritical experiments in an underground facility known as PULSE (Principal Underground Laboratory for Subcritical Experimentation). These tests expose small amounts of weapons-grade material to high explosives to study how the material behaves under extreme pressure, but they are specifically designed to avoid triggering a nuclear chain reaction. The National Nuclear Security Administration has announced plans to increase the frequency of these experiments, while maintaining that there is no technical need to return to full-scale explosive testing.
At Los Alamos National Laboratory in New Mexico, a facility called DARHT uses two massive X-ray machines to capture freeze-frame images of materials imploding at speeds over 10,000 miles per hour. These radiographs show scientists exactly how weapon components behave during implosion, providing real-world data to check against computer simulations. Without actual detonations, this kind of validation is essential for confirming that aging or remanufactured warheads will still function as designed.
At Lawrence Livermore National Laboratory in California, the National Ignition Facility takes a different approach. It uses 192 high-energy laser beams to create temperatures above 100 million degrees and pressures more than 100 billion times Earth’s atmospheric pressure. These are conditions similar to those inside a detonating nuclear weapon. By recreating those extremes in a controlled chamber, scientists can study how weapons materials respond to fusion-level energy without ever setting off an actual bomb. It is the only facility in the country designed to study fusion ignition and thermonuclear burn, the process that gives hydrogen bombs their destructive power.