The idea of a MIRV for the United States was pushed more than a year later by Latter’s brother, Albert, also a RAND physicist who had made the trek to Livermore in the early 1950s, and who was presently sitting as chairman of the Nuclear Panel of the Air Force Scientific Advisory Board. At one panel session in early 1964, General Glenn Kent, who was then in the midst of directing the damage-limiting study, delivered a briefing that suggested there were more Soviet targets than there were U.S. strategic nuclear warheads, especially if one counted all the airfields in the U.S.S.R. that might host Soviet military aircraft. Kent flashed a slide of a typical Soviet airfield, and Al Latter noticed something that led him to a novel observation. The field was strangely shaped—long, narrow, twisting in several different directions. The circle of damage caused by the explosion of a single high-yield warhead would blow up a lot of the territory around the airfield and would not destroy all of the airfield itself. Latter reflected on the RAND memo that his brother had written on multiple warheads and suddenly realized that they could come in very handy in this mission. Several small warheads could much more efficiently destroy the entire airfield and do relatively little damage to the surrounding area.
And there was another bonus. In the official U.S. war plan, 309 Minuteman ICBMs were aimed at 210 Soviet bomber bases, and another 220 gravity bombs were to be dropped from B-52s on the 110 Soviet “aircraft dispersal bases”—nearly 530 weapons in all. Latter reasoned that if one took, say, 100 of those Minutemen and put six warheads on each, they could destroy all the airfields and free the other 209 missiles and the 220 gravity bombs to go after completely different targets.
Latter assembled a group of highly respected weapons scientists, told them about his revelation and said, “Let’s write a report.” It was finished in June 1964, and was signed by the Latter brothers and a gaggle of heavyweights from Livermore and Los Alamos, among them Edward Teller, Johnny Foster, Harold Agnew, David Griggs, Roland Herbst and others whom the Latters had known for years. Al Latter made sure that Glenn Kent and other Air Force generals passed the report to the right people.
Independent of Latter’s efforts, the technology for MIRV was already coming into existence. The U.S. space program had developed what was called a “post-boost control system” that, when attached to the nosecone of a rocket booster and launched into outer space, could fire several satellites, each with its own motor, into orbit. Such a system was first launched in October 1963. The technology involved was very similar to the multiple-warhead system that Dick Latter originally had in mind.
Harold Brown, Robert McNamara’s chief scientist and onetime director of the Livermore Lab, naturally knew about this new space technology, and when his old friend Al Latter showed him the report by the Nuclear Panel on Multiple Warheads, he found the synthesis of science and strategy irresistible. Brown made only one alteration in the recommendation: an existing warhead, called the MK-12, could hold three warheads; he proposed using that instead of some totally new six-warhead contraption that would cover only a few extra targets at much higher cost. Latter concurred.
Meanwhile, McNamara was embroiled in serious disputes with the Air Force over how many Minuteman ICBMs to deploy and with the Army over whether to fund fully the Nike-X ABM. From a bureaucratic standpoint, MIRV was a godsend: by putting multiple warheads on some of the Minutemen, he could persuade the Air Force to accept his decision to field only 1,000 missiles; and he could use the MIRV as yet another weapon in his arsenal of arguments on why an ABM could ultimately be defeated by a Soviet buildup of offensive weaponry. McNamara approved development of MIRV without hesitation, reporting to Lyndon Johnson in his DPM of December 3, 1964, “I intend to… provide for the development of a capability for delivering three MK-12 warheads to geographically separated targets….” The next year, he approved a new version of the Minuteman, called Minuteman III, to be equipped with the MK-12 MIRV.
Publicly, McNamara rationalized MIRV as a way of penetrating enemy ABM systems, saturating them with more warheads than they could handle. But in classified memoranda, he endorsed another mission: going after counterforce targets—not just airfields, but also “hardened” missile silos. Along with his 1964 MIRV decision, as another part of his compromise with the Air Force, McNamara announced, in the DPM to Johnson, the development of a new inertial-guidance system that would improve the accuracy of Minuteman so that “the probability of destroying targets hardened up to 300 psi [pounds-per-square-inch overpressures, roughly the blast-resistance of Soviet ICBM silos at the time] would be in excess of 90 percent.” In his 1965 DPM, McNamara described the Minuteman III, also called the Improved Capability Missile, as having “much greater accuracy, payload and versatility” than its predecessors, promising a much higher “single shot kill probability” against hardened targets. In the 1966 DPM, he noted that his calculation of how many MIRVed Minuteman Ills should be deployed “was arrived at by considering the Soviet military and urban target system in the absence of ballistic missile defenses [ABMs].”
MIRV saved the counterforce strategy from extinction at just the right moment. Through the mid-1960s, McNamara could talk all he wanted about assured destruction, but everyone knew that the real targeting plan was counterforce. The U.S.S.R. had so few strategic nuclear forces, and they were so vulnerable to the effects of blast, that a U.S. arsenal geared publicly toward assured destruction could just as easily execute a counterforce plan as well. But it soon became clear that the Soviets were building more and more ICBMs, meaning that the U.S. would have to build more weapons to cover them. And they were following the Pentagon’s prudent example of encasing their ICBMs in underground concrete silos, meaning that the U.S. would have to make its missiles more accurate, to put the peak of explosive pressures closer to the silo. McNamara’s concessions on MIRV and improved accuracy satisfied both requirements.
The irony was grim. In his efforts to clamp down on Air Force demands for more intercontinental missiles, McNamara gave the service more ICBM-based weapons than it had hoped for in years. In 1962, Air Force officers had requested 2,100 Minuteman ICBMs. By the end of the decade, they were allowed to deploy 550 Minuteman III missiles, carrying a total of 1,650 warheads, and 450 single-warhead Minuteman IIs—a grand total of 2,100 weapons. Just as McNamara was departing from the rhetoric of Ann Arbor, just as he was rejecting counterforce as an unrealistic strategy, his decision on MIRV and improved guidance systems gave the advocates of limited nuclear war fresh cause for hope and glory.
To go much further on this new hope, however, the enthusiasts of NU-OPTS would have to change the nuclear targeting plan, the SIOP. In the late 1960s, the plan still remained essentially the SIOP-63 guidance that Dan Ellsberg had written in the spring of 1961 and that Alain Enthoven and Frank Trinkl had elaborated upon that summer. The officers at SAC’s Joint Strategic Target Planning Staff had kept following this guidance over the years, targeting missiles and bombs on counterforce targets as they emerged, a task for which the MIRVs, once they came on line a few years later, would be ideal. However, the expansion of the Soviet force was creating another problem. In the early 1960s, the U.S. needed to fire only a few hundred weapons to execute Option One of SIOP-63—destroying the Soviet strategic nuclear forces. Now, doing so would require firing a couple of thousand—at least one, often two, for each ICBM silo as well as one or two for each of the bomber bases, possible aircraft-dispersion bases and submarine ports. The critique of counterforce offered by Tom Schelling and, later, Jim Schlesinger—that such an attack would be so massive that the Soviets could not distinguish it from an all-out strike and, so, would respond with an all-out blow themselves—became particularly cogent. Yet this was the smallest strike option in the SIOP.