No first use

No first use refers to a pledge not to use nuclear weapons unless first attacked by an adversary. The former-Soviet Union, now Russia, and the People's Republic of China have both pledged no first use, while the United States did not and has not. The reluctance of the United States to pledge no first use during the Cold War resulted from the numerical superiority of Warsaw Pact conventional forces and the belief that the use of tactical nuclear weapons would have been essential in defending against a Soviet invasion.

In the case of the Soviet Union, a no first use pledge was seen as a means of undermining support for the United States particularly among Europeans on whose territory a nuclear war would be fought.

In the case of China, the limited number and accuracy of its nuclear arsenal rendered it suicidal for any doctrine other than assured destruction and hence it has pledged no first use against other countries. However, it is somewhat unclear if the pledge applies to a conflict involving Taiwan especially in the event of involvement by the United States.

After the end of the Cold War, Russia has continued to pledge no first use in large part because the Russian economy does not allow for the expansion of its nuclear arsenal to serve as anything other than a deterrent force. Despite the fact that a Soviet invasion of Western Europe is no longer likely, the United States has stated that it reserves the right to respond to an attack by weapons of mass destruction with nuclear weapons, and a leaked Pentagon report in March 2002 purports to show that the use of nuclear weapons for new uses (such as destroying deep bunkers) is being considered.