One of the most important and one of the least well understood pieces of the arms control puzzle is the issue of verification. Understanding verification needs and capabilities is important because too often weapons reduction or elimination proposals are rejected with the argument that they cannot be adequately verified. It has been customary in arms control negotiations to insist on much more verification than is necessary. A perfect verification system is impossible, even with quite intrusive means of inspection. For example, it is unlikely that one can verify to the exact number compliance with any agreements that set a numerical limit for missiles or aircraft. Fortunately, this is not the requirement for verification of arms-limitation agreements, any more than it is for monitoring an intense arms race. What really matters is whether or not the inspection system offers a high degree of confidence that it will provide a warning before a dangerous situation develops. It was long ago agreed that a single clandestine test of a small nuclear weapon could not be detected with a high degree of probability, but it was concluded that this was not essential because, as both sides have had to conduct large numbers of tests to develop their nuclear arsenals, one test more or less would not make a significant difference in the quality of either stockpile. A major new development is nor likely to be possible with a single test. Also, a nation that wants to carry out a clandestine series of nuclear explosions without detection, say a set of ten, must convince itself that not even one of them will be detected because, from the inspection viewpoint, a single unequivocal violation is sufficient to sound a warning or even destroy a treaty. Similarly, although it may be impossible to count accurately the exact number of missiles that have been deployed, there can be a high degree of confidence that changes in force size that could create a threatening situation would be detected by unilateral means long before the illegal increases could affect our national security. It is not necessary to be familiar with all possible verification needs to understand that our present verification systems are adequate to do the job. In this volume, you will find chapters by people who are knowledgeable about many different aspects of verification. These chapters are the gleanings of a stimulating and, on the whole, encouraging conference sponsored by the Program in Science and Technology for International Security at the Massachusetts Institute of Technology in 1984. I say "on the whole, encouraging," because the general sense of the conference was that the technical people present were a group that, between them, had looked seriously at all the major verification needs and technologies. And the consensus was that our verification abilities are of a quality to permit confidence that neither violations of agreements nor unilateral declarations of limitations on testing or deployment of nuclear systems can become dangerous to our security. One need only realize how effective the national systems of inspection and verification employed by the United States have been, especially since the late 1950s, to appreciate the participants' confidence in their potential value for the monitoring of arms reduction measures. The United States detected the first Soviet nuclear bomb explosion; it detected the earliest Soviet missile tests; it has unilaterally and with confidence reported on the size of the many components of the Soviet nuclear forces. Many people fear that the certain-to-come reductions in the size of missile systems, the possibility of mobile rockets, and the deployment of the cruise missile will make verification less reliable. That is undoubtedly true. But if the purpose of the verification system or process is to assure discovery of violations and to provide warning of violations of agreements with sufficient lead time to avoid dangerous developments or deployments, the available systems are much more than adequate. Furthermore, as one looks to the future, one can also expect marked improvements on present verification capabilities (some of which are discussed in the chapters to follow). It should be expected also that the nations involved in arms reduction or control agreements would be prepared to permit an appropriate level of inspection when substantial progress has been made in reducing the size of nuclear arsenals. Finally, it is important to realize that effective deterrents do not depend upon matching type for type or unit for unit in either delivery systems or nuclear weapons. Sea-based systems can deter land-based systems. Ballistic missiles can deter cruise missiles, aircraft can offset cruise missiles, etc. The important issue is that there exists a modest but secure retaliatory force, as long as deterrence must remain the peacekeeping strategy. Everyone knows that there already exist enough nuclear weapons to wipe out most of life on our planet in a flash and convert it into a barren, poisoned wasteland. Not so well understood is the fact that there is no acceptable military use for these weapons. By acceptable military use I mean one in which the military advantage is sufficient to justify the disadvantages that appear to accompany their use. Studies of the possibility of carrying out a successful pre-emptive strike, for example, one that disarms the opponent's forces so completely that the retaliatory blow would not destroy the initiator's country, show that this option does not exist. In fact, many millions of people on both sides would die in any substantial nuclear exchange. The only role for nuclear weapons is as a deterrent to their use by others. The only meaningful question is how large a force is required to ensure confidence in the deterrent. And this is a matter of judgment and common sense. A very few nuclear weapons, certain of delivery, constitute an adequate deterrent, one so convincing that it will discourage any nuclear adventurism. Unfortunately, the arms race has taken on a life of its own and has acquired so many supporters and beneficiaries that it dominates the lives of the two major nuclear powers, and especially their leaders, so that there is no time (at least in the United States) for serious and thoughtful study of the nature and consequences of the arms race. Perhaps this spell can be broken by a collective effort to understand the extent of the dangers, followed by a collective effort to work for a significant change in superpower behavior. There are a few issues that, if widely understood and accepted generally, could give the leaders of the superpowers the confidence and courage to move unilaterally to halt the arms race and then reduce the number of nuclear weapons in their arsenals. Furthermore, if these points were clearly understood by most of the people who are basically opposed to the present directions, it would give them the confidence to demand a halt in the massive military commitments. To start with, no one knows how to use nuclear weapons in warfare. There are hundreds of thousands of experts on technical matters and on military hardware. But on the critical issues of strategy, deterrence, warwinning, and damage effects of nuclear weapons on people, physical structures, and the environment, there are truly no experts. None. No one knows for sure about the field performance of nuclear weapons, their reliability, or accuracy. Because it is impossible to test nuclear weapon systems in realistic conditions, uncertainty about their performance in combat overrides the knowledge of the performance of individual components. There has never been a war in which tactical or strategic nuclear weapons were used by both sides. Planners, therefore, are completely dependent on theory to support their strategies. All plans discussed with such solemnity by so-called experts are based entirely on speculation. That is why there is so little agreement among analysts after decades of thinking, writing, and debating about nuclear strategy. The layperson who argues for a nuclear freeze or a test ban or some other arms-limitation measure is frequently dismissed because he or she lacks secret information on the matter. There are no secrets on the vital issues that determine the intensity and momentum of the arms race. Everyone should realize that on the critical issues of what is an adequate deterrent, whether humanity can recover from a nuclear war, and many other such questions, their studied judgments are as good as those of any political or military leader. In fact, they may be even better, because they will have more time to consider the matter and are not subjected to the pressures that impinge on people in high official positions. It is important for people to realize that there is no monopoly on wisdom, no special knowledge that changes the commonsense conclusion that nuclear weapons have only one purpose -- namely, to prevent their use -- and that can be accomplished with a small number of secure weapons on both sides. Similarly, it should be obvious that if both sides believe that they can only get a fair hearing if they bargain from a position of strength, we will not only never stop the arms race, but we will have created conditions that ensure its growth. The determination by both sides to maintain even a five percent superiority will ensure a rapid growth in opposing forces, while a willingness to accept a lesser position of the same size by both would quickly begin the reduction of arsenals. Neither secret information nor specialized knowledge is needed to understand the issues that really matter in shaping the arms race. And, furthermore, on those issues there are no experts whose views should be given special weight in decision making. To the extent that they can be understood at all, the significant facts of those issues can be understood by anyone who is willing to make a sustained effort to do so. A few hours of study and discussion a week can soon make a person knowledgeable if not expert, and a large body of knowledgeable people around the world could improve the dialogue in which the fate of the earth is discussed. This is a volume in which a number of scientists and analysts put forth their special information, the fruits of their experience. They are experts, not on the use of nuclear weapons in war, but on particular technologies and political contexts that are relevant to verification. Though it may not be easy going for the layperson, despite the intent to be clear and to provide guides where the technical going is steepest, it is precisely the kind of reading that will equip people who are concerned about the urgency of reversing the arms race to arrive at and support their own views, as valid as any expert's, on the strategically important verification question. And to join in the dialogue of knowledgeable people, upon the outcome of which all our fates and those of our children and grandchildren depend. Man is at a momentous crossroad. There is still time to stop the runaway arms race and to confront the other dangerous problems of survival, but the opportunity will soon pass. A nuclear war would certainly eliminate that opportunity. So will a few more years of continuing to prepare for one with the necessarily wrong priorities that this requires, which now determine national policies everywhere.