The PTBT was clearly an attempt to make nuclear weapons programs more difficult to sustain, thus limiting nuclear proliferation. The signatories to the treaty agreed that they would no longer carry out any nuclear test explosion in the atmosphere, underwater, in outer space, or in any other environment that would allow the spread of radioactive fallout beyond the territorial borders of the state conducting the test. There was a precedent for an agreement of this kind, namely, the 1959 Antarctic Treaty, the first major international arms control treaty following World War II. Its goal was to prevent the use of Antarctica for military purposes in the belief that it was in humankind's interest to keep the continent pristine and open to scientific research.
World public opinion was already attuned to the dangers of atmospheric nuclear testing as a result of the 1954 Castle Bravo incident, when a thermonuclear weapons test at Bikini Island in the Pacific unwittingly exposed to nuclear fallout 28 Americans, 236 Marshall Islanders, and 23 crew members of the Japanese fishing boat Castle Bravo. Public opinion was further inflamed by France's decision to conduct atmospheric tests in Polynesia in 1962.
Furthermore, in the United States there was increasing support for a test ban throughout the summer of 1963. In early July of that year, 52 percent of Americans signaled unqualified support for a test ban. After the treaty had been signed, 81 percent of those polled approved the ban. During the early 1960s, two developments were influential in pushing forward a test ban. Considerable radioactive materials were being poured into the atmosphere as a result of atmospheric nuclear testing, and the world's nuclear states had advanced their nuclear technology to the point where a combination of underground tests and physical calculations gave them sufficient information to design and test their strategic weapons without the risk of radioactive fallout.
In 1962, the newly established Eighteen-Nation Disarmament Committee (ENDC) within the United Nations (UN) became the principal forum for discussions concerning a test ban. After protracted negotiations, an agreement emerged on the use of seismic stations and on-site inspections for verification purposes, but disagreement on the acceptable number of inspections continued. In July 1963 the United States, Britain, and the Soviet Union initiated tripartite talks on the cessation of nuclear tests in the atmosphere, in outer space, and underwater. The agreement on a partial test-ban treaty came out of those discussions after about three weeks of talks.
The PTBT seemed to offer hope for future disarmament agreements. Following the PTBT negotiations, worldwide concern over nuclear testing and the nuclear arms race in general declined dramatically. In 1968 the Nuclear Non-Proliferation Treaty (NPT) was signed, restricting the flow of weapons, technical knowledge, and fissile materials to states that did not already have nuclear weapons. The United States and the Soviet Union went a step further in 1974 when they signed the Threshold Test Ban Treaty (TTBT). It limited underground testing, which was allowed by the PTBT, to a maximum weapons yield of 150 kilotons, and only at declared testing sites. It also allowed on-site inspection by the other state for any test expected to exceed 35 kilotons. The TTBT did not enter into force until 1990. It had a duration of five years, with five-year extensions, and remains in force today. The Comprehensive Test Ban Treaty (CTBT) was called for in the preamble of the PTBT but was not signed until 1996. As of 2007, the United States had refused to ratify the CTBT, despite being one of the original signatories. Nonetheless, the United States, Great Britain, and Russia have observed unilateral nuclear testing moratoriums since 1992, and the last French test took place in 1995. Jérôme Dorvidal and Jeffrey Larsen
Bamberg, James. British Petroleum and Global Oil, 1950-75: The Challenge to Nationalism. Cambridge: Cambridge University Press, 2000.; Seaborg, Glenn, with Benjamin S. Loeb. Kennedy, Khrushchev, and the Test Ban. Berkeley: University of California Press, 1981.; Sobel, Lester A. Disarmament and Nuclear Tests, 1960–1963. New York: Facts on File Series, Library of Congress, 1964.; Terchek, Ronald J. The Making of the Test Ban Treaty. The Hague: Martinus Nijhoff, 1970.
Jérôme Dorvidal and Jeffrey Larsen