Nuclear deterrence is the threat to retaliate with nuclear weapons. In general, deterrence refers to the attempt to create risks that lead the opponent to not engage in a certain policy or action. For deterrence to work the risk must be disproportionately higher than any possible gain. For nuclear deterrence to succeed certain physical and psychological preconditions have to be fulfilled.
Can nuclear deterrence succeed? For nuclear deterrence to succeed, a threatening nation has to be capable and willing to use its nuclear weapons and must effectively communicate this to the nation that is to be deterred.
First, a deterrent force must be capable to inflict unacceptable damage, or more precisely the threatening nation has to be capable to exact payments (at a cost acceptable to itself) either by denying the opponent to achieve the objectives, by charging the opponent an excessive price for achieving it, or by a combination of the two. A nation has also to guarantee the safety of its nuclear arsenal. There must be no way for the opponent to eliminate the deterrent capability of the threatening nation. Strategists call this "second strike capability," that is the retaliatory force should be protected from destruction through a first strike. A second strike capability can be ascertained not only by technical means but also through policy means. Second, the threatening nation must have the plans and the readiness necessary to demonstrate that it can deliver on its "message." Conveying willingness to use retaliatory nuclear forces creates a dilemma: The threatening nation must show willingness to engage in a war it tries to deter or prevent. Is there a point at which the threatening nation deters itself? Third, the threatening nation must successfully communicate to the opponent the price it will have to pay for attempting to achieve an
unacceptable objective. For the United States conveyance of the deterrent message had two aspects: Deterrence had to address opponent as well as friend. The opponent had to believe in deterrence, and deterrence had to reassure U.S. allies in Europe. Reassurance and deterrence were two sides of the same nuclear coin. For much of the Cold War, deterrence and reassurance complemented each other. Fourth, and most important, the deterrent message must have some degree of credibility. Both nations must believe that there is a real probability that the threatening nation will indeed perform the promised action, if required.
In summary, the components of nuclear deterrence have a physical and a psychological character. On the physical level, deterrence requires a series of military instruments, sufficient to threaten the opponent in a way that it would not even think of attacking. Successful deterrence is guaranteed, however, only if the will is there to use these weapons. Deterrence is credible only if a nation is able to successfully convey the first two points to it's opponent, that it is capable and willing. In other words, successful deterrence depends on psychological components: communication and perception.
How many nuclear weapons would be sufficient for deterrence to work? Strategists and pundits differ in their answer as to the best way to prevent an all-out nuclear war. One camp argues that the world is better off with more and better nuclear weapons. Another camp counters that more and better nuclear weapons increase the chance of accidental or crisis-driven nuclear war. Still, another camp argues in favor of the total abolition of nuclear weapons on the basis of morality, international and humanitarian law.
How can one prove that deterrence works? Some people may argue that the absence of large-scale conflicts after the Second World War proves that nuclear deterrence works. In reality, the efficacy of deterrence is hard to measure. If deterrence works, its effects are almost invisible. Deterrence is assumed to be successful when it prevents policies and actions. In other words, the success of deterrence cannot be proven.
What, if deterrence fails? Nuclear war remains a possibility. What kind of consequences does that have for public policy? Should a country seek a position of nuclear superiority over potential adversaries and fuel a global arms race? Should a country unilaterally disarm or even abolish all nuclear weapons? Would a disarmed country be subject to nuclear blackmail by those who do not disarm? Should we prepare for civil defense and protect key industries while making the idea of nuclear war publicly acceptable? Should we prepare at all for nuclear war?
Can a nuclear war be won? It appears that all world leaders agree that a nuclear war cannot be won. Nevertheless, nuclear weapons research and weapons modernization continue, and so does the proliferation and use of nuclear and ballistic technology. North Korea , Iraq, Iran , India and Pakistan are good examples that military planners have not given up the quest for acquiring a nuclear capability. At least they seem to prepare for the case that deterrence fails. Should deterrence fail a nation might want to have more nuclear weapons at its disposal than are needed for deterrence to succeed.
What are core and extended deterrence? We distinguish between two forms of deterrence: core, or passive deterrence and extended, or active deterrence. Core, or passive deterrence is the threat with a nuclear-strategic response in case of a nuclear attack on the home territory of the threatening nation (for example, the United States). Extended, or active deterrence threatens with a nuclear-strategic response in case of a nuclear attack on the territory or troops of allies (for example, members of NATO). Extended deterrence is called "active" because it involves a clear decision and the willful act on the part of the nation that owns the nuclear weapons (in NATO's case, the United States). Because of its political connotations, "active" was the term preferred by U.S. allies in Europe during the Cold War. U.S. policy-makers preferred the term "extended deterrence," which is rather vague. The choice in words, however, hinted at the political dilemma nuclear deterrence created for the United States. In case of a nuclear exchange, would the U.S. sacrifice New York, Chicago, and Los Angeles for Paris, London, and Berlin?
Source : John Lewis Gaddis, Strategies of Containment : A Critical Appraisal of Postwar American National Security (Oxford University Press, 1982).