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U.S. Department of State

Diplomacy in Action

History of the CTBT

Fact Sheet
Bureau of Arms Control, Verification, and Compliance
April 9, 2012


[This fact sheet has been updated; see current version.]

Key Point: The effort to end nuclear explosive testing has spanned five decades with efforts culminating in the Comprehensive Nuclear Test-Ban Treaty (CTBT), which was opened for signature in 1996.

The first nuclear explosive test was conducted by the United States on July 16, 1945. The Soviet Union followed with its first nuclear test on August 29, 1949. By the mid-1950s, the United States and the Soviet Union were both conducting high-yield thermonuclear weapon tests in the atmosphere. The radioactive fallout from those tests drew criticism from around the globe. The international community’s concern about the effects on health and the environment continued to grow. In 1954, Indian Prime Minister Jawaharlal Nehru proposed a ban on all nuclear testing. The increasing public concern over explosive tests led to the negotiation and entry into force of the 1963 Limited Nuclear Test-Ban Treaty (LTBT). This Treaty banned nuclear testing in the atmosphere, outer space, and under water, but underground tests were still permitted.

When the Nuclear Non-Proliferation Treaty was being negotiated in 1968, a comprehensive test ban was discussed, but the international community failed to reach agreement on the issue. Advocates for a ban on explosive testing persisted.

In 1974, the United States and the Soviet Union signed the Treaty on the Limitation of Underground Nuclear Weapon Tests, also known as the Threshold Test-Ban Treaty (TTBT). It established a nuclear "threshold" by prohibiting the United States and the Soviet Union from conducting tests that would produce a yield exceeding 150 kilotons (equivalent to 150,000 tons of TNT). The mutual restraint imposed by the Treaty reduced the explosive force of new nuclear warheads and bombs, which could otherwise be tested for weapons systems. The TTBT was not intended as a substitute for a comprehensive test ban. Article I of the Treaty states that, “the Parties shall continue their negotiations with a view toward achieving a solution to the problem of the cessation of all underground nuclear weapon tests.”

In 1976, scientists from different countries formed the Group of Scientific Experts (GSE) and began conducting joint research into monitoring technologies and data analysis methods for the verification of a comprehensive test ban.

Almost two decades later, the Cold War ended, bringing with it increased possibilities for progress on disarmament and self-imposed testing moratoriums from the United States and the former Soviet Union. Capitalizing on this momentum, the United Nations disarmament body, the Conference on Disarmament (CD) in Geneva, began formal negotiations on the Comprehensive Nuclear Test-Ban Treaty (CTBT) in 1994. Capitalizing on the GSE’s research, the CD was able to reach consensus on the verification regime. Other parts of the negotiations proved more difficult, but members of the CD were able to find common ground and move forward. Australia submitted the Treaty to the UN General Assembly, where it was adopted on September 10, 1996 and opened for signature on September 24, 1996.

Since then, 183 nations have signed the Treaty, and 157 have ratified it. Of the 44 nations whose ratifications are specifically required by the Treaty for it to enter into force, 41 have signed and 36 have ratified.

For more information on the history of the CTBT, click here.

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