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One result has been the growing determination to stabilize and ideally to reverse the arms race by negotiated agreement. There are at least two unprecedented aspects to the nuclear arms race. The destructiveness of the weaponry sets an upper limit beyond which additions to destructiveness become more and more marginal. At the same time, the complex technology of the nuclear age raises the danger of an automaticity that might elude rational control. For if one side should destroy the retaliatory force of its adversary, it would be in a position to impose its terms. That prospect could tempt the intended victim to undertake a "preemptive" first strike—or launch its weapons on warning. Mutual fear could turn a crisis into a catastrophe. Proponents of arms control thus saw it as their immediate objective to reduce the incentives and possibilities of surprise attack.
The goal was to reduce the vulnerability of strategic forces by maintaining symmetrical numbers of strategic weapons. If neither side could hope to destroy its opponent, the incentive for surprise attack would disappear in the face of certain and intolerable retribution. So long as missiles had single warheads and airplanes needed hours to reach their targets, a surprise attack would require a vast numerical preponderance. (Even with highly accurate missiles, an attacker probably would not risk a first strike without two warheads for each target, to allow for malfunctioning, hardened targets or errors in accuracy.)
In these circumstances, numerically equal retaliatory forces were rightly conceived as adequate insurance against surprise attack. The optimum total should be large enough so that it could be overwhelmed only by a violation of the agreement too large to be hidden. Yet it should involve a ceiling that would stop the accumulation of strategic weapons. This was the intellectual basis of the arms limitation talks proposed by President Johnson and implemented by President Nixon.
During 1969 and 1970, the Nixon Administration undertook painstaking studies to determine the lowest level above which a strategically significant violation could not be concealed. The culmination was the SALT agreements of 1972. These accords severely limited antiballistic missile defenses to discourage an aggressor from believing he could launch a surprise attack and then defend against a counterblow. The agreements also froze the number of offensive missiles for five years. At that point the Soviets had a numerical edge in missiles—though not nearly enough for a surprise attack with single warheads. But this advantage was counterbalanced, first, by our very large—and growing—advantage in warheads, since only we possessed MIRVs (Multiple Independently Targetable Re-Entry Vehicles) and, second, by our insurmountable superiority both in numbers and in the technology of long-range bombers, on which there was no limitation.