Weapon Testing

Between 1945 and 1992, the United States conducted 1,054 nuclear tests. The first test, Trinity, took place in the southern New Mexico desert on July 16, 1945. The last test, Divider, occurred on September 23, 1992, deep underground at the Nevada Test Site.

Atmospheric Testing

Atmosphere tests were conducted in the Pacific and Atlantic Oceans as well as at the Nevada Test site. The Marshall Islands, in the central Pacific, became the principal test area for the United States, beginning with Operation Crossroads at Bikini Atoll in 1946.

"Oak" Shot, 1958

Later tests, including the first test of a hydrogen bomb, were conducted at Enewetak Atoll. The largest United States test, the Bravo Shot, took place at Bikini Atoll in 1954. Atmospheric tests in the Pacific also were conducted at Johnston Atoll, Christmas Island, and in the deep water off San Diego. One test series, Argus, took place in the South Atlantic Ocean in 1958.

Underground Testing and Test Moratoria

Between 1958 and 1961, the United States and the Soviet Union adhered to a test moratorium initiated by the United States. When The Soviet Union resumed testing in 1961, so too did the United States. Worldwide concern about radioactive fallout from atmospheric tests led the United States and Soviet Union to ratify the Limited Test Ban Treaty and begin underground testing in 1963. Although mostly conducted at the Nevada Test Site, underground tests also took place in Colorado, Mississippi, New Mexico, and Alaska. The largest underground test, shot Cannikin, took place on Amchitka Island, Alaska, in 1971. In 1992, President George H.W. Bush announced a second unilateral moratorium on testing, which Presidents Bill Clinton and George W. Bush subsequently extended. Despite tests conducted by France, Pakistan, and India in the late 1990s, the United States continued the 1992 moratorium to this day.

Los Alamos scientists used these tunnels at the Nevada Test Site to conduct underground tests of nuclear devices until the United States declared a nuclear testing moratorium in 1992.