Why was the 1963 Partial Test Ban Treaty (PTBT) important?

The signing of the PTBT marked the first time the world witnessed real progress on a nuclear test ban.

Signed by the United Kingdom, the United States and the Soviet Union on 5 August 1963, the PTBT banned nuclear testing in the atmosphere, underwater and in space, stating that signatory states could not “carry out any nuclear weapon explosion, or any other nuclear explosion…in the atmosphere; beyond its limits, including outer space; or under water, including territorial waters or high seas”. Although it signaled progress towards a comprehensive test ban treaty, the main effect of the PTBT was that environmental issues were addressed rather than a decrease in testing activities: testing went underground, which was not prohibited by the PTBT.

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