In nuclear ethics and deterrence theory, no first use (NFU) refers to a type of pledge or policy wherein a nuclear power formally refrains from the use of nuclear weapons or other weapons of mass destruction (WMD) in warfare, except for as a second strike in retaliation to an attack by an enemy power using WMD. Such a pledge would allow for a unique state of affairs in which a given nuclear power can be engaged in a conflict of conventional weaponry while it formally forswears any of the strategic advantages of nuclear weapons, provided the enemy power does not possess or utilize any such weapons of their own. The concept is primarily invoked in reference to nuclear mutually assured destruction but has also been applied to chemical and biological warfare, as is the case of the official WMD policy of India.