Deterrent Effect - By Bates Gill

After two decades of steep reductions, the pace of nuclear disarmament has begun to slow. According to data from the Stockholm International Peace Research Institute (SIPRI), the world's nuclear armed states still possess about 4,400 operational nuclear weapons -- 2,000 of which are kept on high alert -- and some 14,600 additional warheads are in storage for possible use. About 95 percent of these weapons of mass destruction -- around 18,000 warheads -- are held by Russia and the United States, more than 20 years after the end of the Cold War.

Of course, nuclear disarmament was always going to be hard slogging. Many decision-makers have a deep interest in retaining these weapons for political and security reasons. And, yes, there is a certain accepted comfort level, or even complacency, with the decades-long existence of nuclear weapons and the dark logic of deterrence. Even under these conditions, nuclear disarmament has seen some significant progress in recent years -- but only as long as nuclear-armed parties believed deterrence could be preserved even as overall numbers of nuclear weapons were reduced.

Looking ahead, however, the longstanding theories of nuclear stability are likely to come under increasing strain with the continued development of advanced conventional weapons technologies that can substantially affect nuclear capabilities. Such technologies are not entirely new, but their improved effectiveness -- especially as overall numbers of nuclear weapons decrease -- increasingly erodes what has been a traditional operational and doctrinal distinction between nuclear and conventional forces. This in turn raises critical questions about nuclear postures and deterrence strategies, which will affect disarmament efforts.

What are some of these conventional capabilities? Let's look at three that have received a good bit of attention.

Perhaps the best known are anti-ballistic missile technologies, or missile defenses, which come in a variety of forms and missions. But in a nutshell, these are weapons systems that can track, intercept, and destroy an enemy missile. Current versions of these weapons tend to be of the "kinetic kill" variety -- a "bullet hitting a bullet" -- but other forms, such as directed-energy weapons (e.g., lasers), have also been explored.

Strategists have long debated the impact of missile defenses on nuclear stability; after all, if one side can entirely negate the other's ability to launch a nuclear strike, then it may not be deterred from launching one itself. Missile defenses were an early sticking point in arms control negotiations between the United States and the Soviet Union -- and they remain one today. Judging from Moscow's repeatedly expressed concerns about America's growing anti-ballistic missile capabilities and the impact its leaders claim they have on Russia's deterrent, further bilateral reductions will surely be slowed.

Countries that have a far smaller arsenal of nuclear weapons and delivery systems -- for example, China has perhaps only 30 to 40 nuclear-armed missiles with ranges capable of reaching the U.S. mainland -- are especially concerned about advances in anti-ballistic missile technologies. Their answer? More missiles with more modern capabilities. And, to further complicate the picture, countries such as China, Russia, and India are pursuing their own anti-ballistic missile capabilities as well, which will in turn affect their potential nuclear adversaries' thinking about the wisdom of smaller arsenals.

A second set of conventional weapons capabilities are conventional long-range (or global) precision-strike weapons. In the United States, such systems -- which fall within the Prompt Global Strike initiative -- have gained some currency over the past decade as the result of a perceived need to be able to attack targets anywhere in the world with great accuracy, to do so quickly, and, if necessary, to do so from the U.S. homeland and not from forward bases. The types of systems foreseen for this mission would include long-range missiles converted from a nuclear to a conventional role.