To determine the effectiveness and other properties of a given nuclear weapons design, the easiest method is a test session. Modern supercomputers in certain countries can model nuclear explosions quite well, decreasing the need for actual tests. Nuclear weapons testing has occurred since 1945, when the world's first atomic bomb was detonated at the Trinity site in New Mexico. In 1963, the Limited Test Ban Treaty, which was written to slow the nuclear arms race as well as prevent the release of harmful nuclear fallout into the atmosphere, forbade atmospheric, ground-based, and water-based testing of nuclear weapons among its signatories. In 1996, the Comprehensive Test Ban Treaty forbade all forms of nuclear testing among its signatories, though non-signatories India and Pakistan tested nuclear weapons in 1998. North Korea tested a nuclear weapon in 2006, sparking outrage in the international community.
The United States is the biggest tester of nuclear weapons, having tested over 1,000 bombs between 1945 and 1992. These ranged in yield from as little as equivalent to a ton of TNT to 15 megatons for the Bravo test. In 1976, the United States and the USSR limited the maximum yield of underground tests to 150 kilotons, using the Threshold Test Ban Treaty. Primary nuclear weapon testing sites for the United States were the Nevada Test Site, near Las Vegas, for earlier tests of smaller yield, and the Pacific Proving Grounds in the Marshall Islands, for larger tests. Although over 925 bombs were exploded at the Nevada Test Site, 75% of all testing, they only make up about 15% of total yield of all US tests. The 125 bombs exploded at the Pacific Proving Grounds were responsible for about 80% of total yield.
Earlier tests placed soldiers and observers only a few miles away from the test sites. Increased yields for future explosions required greater distances from the detonation point or underground tests to protect the surrounding population. The Soviets are responsible for the largest nuclear test of all time, the 50 megaton Tsar Bomba, which could cause third-degree burns from 62 miles (100km) away. Testing has determined that nukes in the 5 megaton+ range could destroy large portions of an entire major city. Because the United States put a greater emphasis on accuracy over yield, their bombs tended to be smaller than Soviet variants, which were made to produce damage even under low accuracy.
