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
Israel is widely believed to have been the sixth country in the world to develop nuclear weapons, but has not acknowledged its nuclear forces. It had "rudimentary, but deliverable," nuclear weapons available as early as 1966. Israel is not a party to the NPT. Israel engages in strategic ambiguity, saying it would not be the first country to "introduce" nuclear weapons into the region, but refusing to otherwise confirm or deny a nuclear weapons program or arsenal. This policy of "nuclear opacity" has been interpreted as an attempt to get the benefits of deterrence with a minimum political cost.