An antiballistic missile defense with the goal of denying the other side's deterrence by means of nuclear retaliation against the society itselfpopulation and industryhas an extraordinarily difficult task. Fundamentally, this difficulty arises because the enormous destructive power of a nuclear weapon means that a half-megaton weapon could kill a half million people; a weapon plus delivery system costing $10 million to $100 million could destroy value on the order of $500 billion (assuming $1 million per life). Another metric compares how much it costs the offense to overcome the defense and, ultimately, the cost exchange ratio between offense and defensenot for holding the damage precisely constant, but retaining a similar magnitude of damage.
In general, defense can be very costly if the requirement is to maintain near-perfect protection against a responsive adversary. The offense, for instance, can choose the specific target; can exhaust the local defense with warheads, dummies, or decoys; or can use enough weapons to leak through the imperfections if not to overwhelm the defense; or can attack the defense specifically ("the eyes of the system," for instance, which are often more fragile or more visible than the targets themselves).
This essay is not itself a book on the future of deterrence and warfare, centered on missile defense; rather, it is a sketch of the current situation regarding tactical and strategic missile defense, with indications of the relationship to deterrence and warfare.
This essay is informed by the author's involvement with strategic offensive and defensive forces since 1952 and with every successive generation of proposal or deployment of ballistic missile defenses.
Indeed, the revolution in microelectronics, radio frequency technology, and signal processing has wrought a revolution in the reliability and effectiveness of radar detection of objects in space or in the atmosphere, and this has been augmented by major advances in optical detection capability both in the visible and the infrared (IR).
So it is commonplace in the United States or elsewhere to read about or to see videos and photographs of test intercepts taking place in the vacuum of space, or in the atmosphere.
In the 1950s or thereabouts, effective intercept could be conceived only with a nuclear-armed interceptor, and the one strategic ABM system briefly deployed in the United States (Safeguard) was equipped with low-yield nuclear warheads on its short-range interceptor. The exo-atmospheric interceptor was to be equipped with a multimegaton warhead not only to compensate for inaccuracy in intercept but also to be able to destroy spaced warheads and decoys.