Two events contributed to a decision to establish a continental nuclear test site in Nevada. The first was the shock of the Soviet nuclear test on August 28, 1949, which stimulated the nuclear weapons program in the United States. The second was the fact that the Korean War reduced the Navy's capability to support nuclear tests at the Pacific Proving Grounds. High yield atmospheric shots, those over about 70 kt, had to be fired in the Pacific. However, most of the nuclear weapons tests were of much lower yield and could safely be fired in Nevada.
The four decades of the Nevada Test Site (NTS) witnessed four major nuclear weapons thrusts: The development of smaller, more efficient, fission weapons; the development of primaries for thermonuclear (TN) weapons; the exploration of new TN concepts; and the design of modern weapons for advanced weapons delivery systems.
It was vastly easier, and less expensive, to field a test series in Nevada than it was at the Bikini or Enewetak Atolls. In the early days, Los Alamos National Laboratory and Lawrence Livermore National Laboratory viewed Nevada as a "back yard" range that provided the opportunity to rapidly test new ideas or answer time-urgent questions prior to committing the resources necessary for a high yield detonation at the Pacific Proving Grounds.
Continental testing, which began in Nevada in January 1951, also offered the opportunity to more realistically assess the effects of nuclear weapons on a wide variety of targets.
The responsibilities for exploring the effects of nuclear weapons fell mainly to the Department of Defense. It quickly became clear that the effects were much more complicated than anyone imagined. An experimental program began with Operation CROSSROADS at Bikini, during the summer of 1946, and continued through the Hunters Trophy event at the NTS on September 18, 1992. That, incidentally, was the next to the last shot that the United States fired prior to the 1992 moratorium.
The DoD was interested in using nuclear tests to indoctrinate combat troops in the nature of a nuclear war-fighting environment. Thus the Desert Rock exercises were born at the NTS. Tens of thousands of military personnel were involved as observers or maneuver troops throughout most of the test operations where shots were fired in the atmosphere.
In addition, federal and state organizations responsible for civil defense matters were major participants at the nuclear tests of the 1950s.
Initially, there was relatively little public concern with radioactive fallout. However, the laboratories and the AEC looked for ways to reduce the fallout by going ever higher, above the surface of the earth, with the nuclear tests. An alternative approach was to go underground, either to reduce the fallout or to eliminate it altogether. Livermore fired the first fully contained shot, Rainier, in a tunnel at the NTS, in mid-September 1957
There was a moratorium on nuclear tests beginning on the first of November, 1958. The Soviets broke the moratorium when they resumed testing in September, 1961.
Following the limited test ban treaty of 1963, which prohibited testing in the atmosphere, both Livermore and Los Alamos went to stemmed shafts for nuclear weapons development shots, while the DoD and Sandia Laboratory went to tunnels for the weapons effects tests. The era of testing in the Pacific had ended. By the early 1970s the testing technology achieved a level where no radioactive release was the norm.
One of the major advantages of testing underground was that higher yield shots could be fired. The largest test fired underground in Nevada was Boxcar in April of 1968. It had a yield of 1.3 megaton.
The last shot before the United States again entered a moratorium was Divider, fired on September 23, 1992.
One hundred shots were fired in the atmosphere and 921 underground at the Nevada Test Site over almost 42 years.