McNamara had never favored a full first-strike capability. In the first DPM, McNamara had spent three short paragraphs briefly listing some drawbacks to a first-strike strategy. In the second DPM, just to ensure that Ann Arbor was in no way to be confused with Air Force philosophy, he devoted four pages to describing the futility of such a strategy.
McNamara did continue to hang on to the essence of the RAND doctrine. “We might try to knock out most of the Soviet strategic nuclear forces, while keeping Russian cities intact, and then coerce the Soviets into avoiding our cities (by the threat of controlled reprisal) and accepting our peace terms…. I believe that the coercive strategy is a sensible and desirable option to have in second-strike circumstances in which we are trying to make the best of a bad situation.” However, whereas the coercive strategy served as the main rationale for the forces McNamara had decided to buy in the 1961 DPM, he now stated, “We should stop augmenting our forces for this purpose when the extra capability the increments offer is small in relation to the extra costs.”
Nevertheless, the Air Force and, by this time, the entire JCS kept up their pressure for more weapons, rationalizing their wish lists with language deliberately modeled on the Ann Arbor speech and in McNamara’s DPMs. Increasingly, McNamara began to fear that the counterforce strategy presented no logical limit to the size of the arsenal; that as long as targets of potentially military value could be found or as long as the Soviets added more weapons to their own arsenal, someone could always claim we did not have enough; that his own endorsement of counterforce was promoting an unlimited nuclear arms buildup that he had gone out of his way to suppress.
In January 1963, McNamara instructed his staff that they were no longer to cite counterforce as the official Pentagon strategic concept. His staff proceeded to inform the military that they were no longer to use counterforce as a rationale for their weapons requirements or proposals. Meanwhile, McNamara had to find some new doctrine that could be used as a further rhetorical tool to clamp down the threat from the JCS. He found the ideal device in the 1960 study known as WSEG-50, which advocated a strategy of city destruction and “finite deterrence.” McNamara’s chief analysts, Charlie Hitch and Alain Enthoven, both from RAND, hadn’t liked that part of WSEG-50, and had urged McNamara to hear Bill Kaufmann’s counterforce briefing. McNamara ended up agreeing with Kaufmann’s points on avoiding cities and trying to control the nuclear war; but he was still attracted to the philosophy of WSEG-50, in that it suggested a basic guideline for determining how many weapons were enough.
In the next DPM, delivered to President Lyndon B. Johnson on December 6, 1963, two weeks after John Kennedy was assassinated in Dallas, McNamara devised a criterion by which nuclear adequacy should be measured, and he called it “Assured Destruction.”
The new measure put almost total emphasis on the deterrence, rather than on the fighting, of nuclear war. Essentially, it said that after a surprise Soviet counterforce strike, the United States should still have enough forces surviving to destroy the U.S.S.R.’s governmental and military controls as well as a large percentage of its population and industrial base. The idea was that as long as the Soviets knew that we could retaliate, that would deter them. McNamara’s Whiz Kids calculated that the Soviets would be sufficiently deterred if we could kill 30 percent of their population and destroy half of their industrial capacity, and, further, that this task could be accomplished with the explosive power of 400 megatons.
It all appeared scientific and precise, but in fact it had little to do with any formulation of how much would be enough to deter the Soviets. It was the output of a computer program designed by Alain Enthoven, “laying down” one-megaton bombs against Soviet cities and calculating, at various points, how much additional damage one additional bomb would do. From this calculation, Enthoven generated a graph with two curves, one showing how many people would be killed, the other how much industry destroyed, as a function of “delivered one-megaton warheads.” Beyond 400 megatons, by which point all major cities would be devastated, the curves began to flatten considerably. And they happened to show that 400 megatons would kill about 30 percent of the Soviet population (assuming a limited urban fallout-shelter program) and destroy about half its industrial capacity. If the U.S. doubled its megatonnage to 800, Soviet fatalities would rise by only about ten percentage points and the industrial capacity destroyed would be boosted by only three percentage points.
In short, the 400-megaton requirement was based on the concept, familiar to all economists, of “diminishing marginal returns.”
* Not including deaths caused by radiation, fallout or firestorm.
There was another reason for the 400-megaton requirement. Enthoven had calculated that after a reasonably successful Soviet first-strike, launched in 1969, and assuming that McNamara’s five-year defense plan of 1964 had been adopted, the United States would be left with at least 1,200 megatons. If one stretched the Assured Destruction calculus to read that there should be 400 survivable megatons on each “leg” of the strategic “Triad”—the ICBMs, the SLBMs and the long-range bombers—that would add up to 1,200 megatons. In other words, Assured Destruction was adopted by McNamara primarily as a tool for beating back the excessive demands of the military, for proving that his own program was adequate for deterrence.
For all of McNamara’s elaboration of the new counter-city strategy, the actual U.S. targeting plan remained the revised SIOP-63 that McNamara had ordered in the spring of 1961. In the 1963 DPM, just below “Assured Destruction,” McNamara endorsed a strategy of “Damage-Limiting,” which was another name for counterforce. And he reiterated the language from the 1962 DPM supporting the “coercive strategy” as “a sensible and desirable option to have in second-strike circumstances”—though he did add the significant proviso, in 1963, that this option did not “provide a basis for buying more missiles.” McNamara also emphasized in the 1963 DPM that he was calculating “the destructive capacity of our force on the hypothetical assumption that all of it is targeted on cities, even though in fact we would not use our forces in that manner if deterrence failed” (italics added).
In fact, in the same 1963 DPM in which McNamara backed Assured Destruction, various charts revealed that by 1969, under his proposed program, only 18 percent of the portion of the U.S. strategic nuclear force on constant alert—or 533 missiles, including all fifty-four Titan ICBMs and about three-quarters of the Polaris SLBMs—would actually be targeted against cities. The other 2,720 weapons on alert—bombers, Minuteman ICBMs, remaining Polaris missiles at sea—would be aimed at bomber bases, missile and air-defense sites, submarine pens, weapons-storage depots, tactical interdiction targets, in short, at counterforce targets. Even the 533 missiles targeted on cities would be aimed to knock out the control centers of the Soviet government and military structure. Although at least 30 percent of the population would be killed and half the industry destroyed, that was not the actual motivation behind the targeting. Finally, these counter-city missiles were to be held in reserve for as long as possible.
McNamara talked Assured Destruction, even in Top Secret memoranda to the President; but the actual targeting strategy, which McNamara closely monitored and approved, remained mainly counterforce. In the early-to-mid 1960s, the Soviets did not have very many nuclear weapons, nor were many of them hardened to any significant degree. The 1,200-megaton alert force that McNamara proposed was rationalized as an Assured-Destruction 400-megaton arsenal times three, for each leg of the Triad; but it was also enough to deliver a powerful counterforce blow. Assured Destruction was adopted by McNamara primarily as a tool for beating back the excessive demands of the military and the JCS. In the event of war, he could still choose counterforce.