Weapon of mass destruction
The only country to have used a nuclear weapon in war is the United States, which dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki during World War II. There are eight countries that have declared they possess nuclear weapons and are known to have tested a nuclear weapon, only five of which are members of the NPT. The eight are China, France, India, North Korea, Pakistan, Russia, the United Kingdom, and the United States.
List of states with nuclear weapons
In 1979, there was a detection of a putative covert nuclear test in the Indian Ocean, called the Vela incident. It has long been speculated that it was a test by Israel, in collaboration with and support of South Africa, though this has never been confirmed. South Africa could not have constructed such a nuclear bomb until November 1979, two months after the "double flash" incident.
South Africa signed the Nuclear Non-Proliferation Treaty in 1991.