In August 1985, on the 40th anniversary of Hiroshima, Mikhail Gorbachev announced that the Soviet Union had halted all nuclear weapons tests and invited the United States to do likewise. Despite exhortations by columnists and arms-control advocates, the Reagan administration has thus far ignored Gorbachev's offer.
At first glance, such a stance appears nothing more than mindless hawkishness. After all, both the United States and the Soviet Union possess enough nuclear weapons to destroy each other as functioning societies. Why continue testing so as to continue building more of these horrible instruments of mass destruction? Besides, unlike other forms of arms control, where cheating is a major problem, nuclear explosions are hard to hide. If the Soviets were to cheat, it's unlikely they could hide the fact, and we could resume testing, too.
Would that the world were so simple! In fact, if your concern is with minimizing the threat of mass destruction posed by nuclear weapons, then you should favor continued nuclear testing, not a ban. The reason has to do with the evolution of nuclear weapons and guidance systems over the past 40 years.
The nuclear weapons of the 1940s and '50s were crude, brute-force devices. They are often referred to as "city busters" because that is all they were good for. The delivery systems, initially manned bombers and later on the early ballistic missiles, were so inaccurate that the warheads were made very large—in the multi-megaton range—to compensate. That way, a miss really was as good as a mile, but at the price of awesome destruction.
By the '60s, guidance-system technology began to improve dramatically, and warhead sizes began to decrease. Today's U.S. ballistic-missile warheads are typically in the range of several hundred kilotons, and while the Soviets still have many warheads larger than a megaton, their warheads' average size has been steadily dropping as well.
But even today's newest ballistic missiles are still only accurate to within a thousand feet or so. The real breakthroughs in guidance have occurred with cruise missiles. These tiny, jet-powered weapons have "active" guidance systems that can home in on a specific target (rather than simply being aimed and lobbed, as ballistic missiles are).
Cruise missiles can be made accurate to within tens of feet, rather than tenths of miles. So they require warheads substantially less destructive than ballistic missiles or bombers. That, in turn, means they can be used against a military target without wiping out the adjacent city and its population.
Most of the present U.S. nuclear arsenal consists of large, old, inaccurate weapons—especially the bombs carried on B-52 bombers, the warheads on Minuteman II land-based missiles, and the warheads on the Poseidon sub-launched missiles. Should nuclear deterrence ever fail, and a war break out, the use of those weapons (and their Soviet counterparts) would wipe out cities and risk causing nuclear winter. The use of cruise missiles would not. It is imperative—morally imperative—that the old weapons be retired and replaced with smaller, accurate weapons usable against military targets.
A comprehensive nuclear test ban, however, like a nuclear freeze, would make it impossible to carry out this essential modernization. Nuclear-warhead design is an iterative process, like every other form of technology. New designs and modifications of existing designs must be tried out to see whether they work before being put into production. A test ban would therefore preclude the very modernization that can make the world safer.
However much we might wish it, nuclear weapons cannot be disinvented. And until a robust set of defenses against nuclear attack is actually in place, we dare not risk giving up some form of nuclear retaliatory force. But we can and must make progress toward a world where mass destruction is no longer the basis of our nuclear policy. A "build-down" to small, accurate warheads is an important step in that direction. It will only be possible if we can continue to test new high-tech warheads as they are developed.