As World War Two approached its conclusion, the U.S. grew increasingly concerned about the potential challenge posed by the Soviet Union. Initial plans called for an inordinate reliance upon the use of nuclear weapons to deter, and potentially defeat, the Red Army and its Warsaw Pact allies. This strategy was rooted in the belief that Soviet forces enjoyed massive conventional superiority but lagged behind the United States in nuclear weapons development. In the late 1940s when the U.S. still enjoyed a nuclear monopoly, for example, American intelligence estimated that the Soviets could deploy 245 combat divisions and 15,000 aircraft, numbers which, it was projected, would enable them to overrun Western Europe in only 45 days. Planners’ initial assessments for countering this projected American force requirements of 90 divisions, which would have equaled levels fielded during World War Two. With the Joint Logistics Plans Committee determining this level of mobilization to be infeasible, Plan Broiler, a nuclear bombing campaign against the USSR to reduce its war-making ability, was proposed. These concerns also shaped NSC-68, which emphasized Moscow’s ability to coercively direct a far greater proportion of its economy toward war efforts and noted that the USSR could simultaneously attack the UK, Scandinavia, the Iberian Peninsula, and Middle East after rapidly seizing Western Europe.
This thinking ultimately paved the way for Eisenhower’s New Look policy, which was based upon a pessimistic assessment of America’s ability to affordably resist a Soviet attack with conventional forces–at this point, it was estimated that the Soviets had 300 active and reserve divisions to America’s 36–and thus advocated for a massive nuclear retaliation in response to any Soviet military aggression, irrespective of Moscow’s use of nuclear weapons. Eisenhower recognized that the U.S. had a clear nuclear advantage, especially given its much larger nuclear arsenal, faster nuclear production rates, and superior airborne delivery systems. Consequently, he believed the prudent approach would be to forgo costly conventional rearmament by purchasing relatively less expensive nuclear weapons. This view was bolstered by Congressional aversion to large-scale troop commitments to Europe, as Congress felt this represented an unnecessary expense and would only encourage European free-riding. Substituting nuclear weapons for troops seemed to be the perfect solution.
But as the 1950s progressed, this extreme reliance on nuclear retaliation became increasingly untenable. Even before Eisenhower assumed the presidency, Dean Acheson was warning that the U.S. must “move ahead under this protective shield [of nuclear weapons] to build a balanced collective force in Western Europe that will continue to deter aggression after our atomic advantage has diminished.” Perhaps the greatest impetus for Acheson’s admonition was Moscow’s growing nuclear arsenal and quickly-improving set of delivery systems, a development clearly demonstrated by the launch of Sputnik. As Soviet nuclear forces expanded, it became increasingly less credible for the U.S. to threaten massive retaliation against even relatively moderate Soviet aggression. Questions about Washington’s willingness to trade Bonn for Boston became increasingly salient, and thus a fundamental reconceptualization of U.S. nuclear strategy became necessary. The other major development, largely due to the emergence of new independent sources of analysis within the Pentagon, was the realization that the size of Soviet forces had been massively overestimated. Instead of confronting an overwhelming horde of communist soldiers, NATO actually faced a force against which it enjoyed rough parity and even, at least within certain domains, superiority. These factors worked in tandem, with Soviet nuclear expansion creating the need for a new type of strategy and revised estimates of Soviet conventional power offering the potential for a new, more effective strategy.
The issues created by the growth of Soviet nuclear forces were apparent even before the Kennedy administration pursued flexible response in earnest. NSC-68 noted the potential challenges to American nuclear strategy that the development of nuclear forces and air defense systems might pose. Specifically, it highlighted the immense destructive power the Soviets might have by the mid-1950s while also warning that the effectiveness of American nuclear strikes could be degraded due to improved Soviet fighter aircraft and air defense systems. The report therefore worried about incremental Soviet probing attacks under the shield of their nuclear weapons and called for a broad-based buildup of American forces. The Soviet development of missile delivery systems in the mid-1950s created concerns about the American ability to credibly threaten a nuclear strike. This problem was only exacerbated by the Soviet development of multi-megaton thermonuclear warheads, which threatened massive damage to the U.S. homeland. In short, it was no longer credible to believe that the U.S. could conduct a nuclear strike and suffer only minimal damage from Soviet retaliation. But Eisenhower’s commitment to austere defense spending and the bureaucratic power of the Strategic Air Command, which had an incentive to promote a strategy based largely around strategic nuclear bombing given the budgetary largess this afforded it, made a transition from massive retaliation more difficult.
But the problem of growing Soviet power did not diminish, and indeed baseless concerns about bomber and missile gaps made the Soviet nuclear threat appear even greater that it was. The Kennedy administration, therefore, was forced to adjust Eisenhower’s approach to better reflect the new strategic reality. Not only did Kennedy’s team view the threat of massive retaliation as theoretically dubious but they also believed it was empirically ineffective at deterring aggression given Pyongyang’s invasion of its southern neighbor despite the existence of American nuclear weapons. America’s objective of containing the threat of Soviet power and promoting and defending the U.S. and the democratic system outlined in NSC-68 had not changed, but the strategy for achieving these goals was being revised.
Instead of relying exclusively or even primarily on strategic nuclear weapons to deter Soviet aggression, the Kennedy team sought to prioritize conventional forces. They felt that these forces would offer a far more credible deterrent against Soviet aggression. Another benefit was the range of missions these kinds of forces could undertake: multimegaton nuclear devices are useful only in full-scale nuclear war, but conventional forces could perform a range of missions ranging from military signaling to low-intensity interventions to large-scale conventional conflict. The initial plan was that many of these forces would be based in the U.S. and deployed to crisis spots as needed. Indeed, the Kennedy administration’s end strength goals were determined by evaluating the number of divisions needed to supplement indigenous forces across a range of potential military theaters. Ultimately this force posture proved unworkable because of insufficient logistical capacity to surge large numbers of troops to hotspots and because of allied resistance to U.S. efforts to pull forces back to the continental United States. As a result, the Kennedy administration’s posture was not as flexible as had been originally envisioned, but it still represented a marked shift away from the nuclear-centric massive retaliation doctrine of the Eisenhower administration.
The shift toward emphasizing more flexible conventional forces did not face only logistical and alliance constraints, however. There was also the matter of the supposed quantitative superiority of Warsaw Pact forces. After all, Soviet conventional superiority was one of the primary reasons that the U.S. adopted the strategy of massive retaliation. Threats to deploy conventional forces might be more believable, but they would not be any more effective at preventing a significant Soviet conventional attack than nuclear weapons because of the degree to which they were believed to be outnumbered. Thus, the credibility problem remained. Part of the solution was to continue to rely on lower yield tactical nuclear weapons to increase the power of U.S. and NATO conventional forces without necessarily having to resort to powerful strategic nuclear strikes on the Soviet homeland. This certainly mitigated conventional force disparities, but it also led to new problems. For example, the use of tactical nuclear weapons would likely elicit a proportionate Soviet response, but the much higher casualty rates incurred during a tactical nuclear exchange could favor the Soviets given that they were believed to have far greater available manpower.
This vexing situation suggested the need for a more careful evaluation of the relative conventional balance in Europe, and this led to some paradoxical observations. Work by General Maxwell Taylor showed that the perceived massive imbalance in conventional forces was counter-intuitive because NATO had both a larger population and significantly greater economic power than the USSR and its Warsaw Pact allies. Further assessments by Systems Analysis and ISA echoed this observation, concluding that the Soviets should actually face a more difficult challenge in matching NATO power rather than the converse. Thus, it seemed strange that the communists should enjoy such an enormous advantage in military power – at this point they were estimated to have 175 divisions to NATO’s 25. Indeed, more detailed estimates revealed that if the Soviets were to equip their ground forces to the same level as that of the Americans, they would need to be spend around 17.5 billion dollars, the amount the U.S. was spending on procurement for its entire military. Either the U.S. and its allies were monumentally inefficient in their training and equipping of forces or the estimated numbers for Soviet force strength were grossly overestimated.
Similarly implausible estimates existed in comparisons of air power. Analysts in the early 1960s assessed that NATO was outnumbered 3:1 in deployed combat aircraft. This number was difficult to fathom in its own right, but it was especially incredible given the extreme disparity that already seemed to exist on the ground. Simply put, it did not seem possible that the Soviets and their allies could have a substantial absolute advantage in the air and ground domains while having fewer people and a smaller economy.
To resolve these paradoxical estimates, McNamara tasked independent centers of analysis like ISA and Systems Analysis to check these assumptions and more rigorously estimate Warsaw Pact end strength. These analysts, unlike the services, had no incentive to exaggerate threats for budgetary reasons, and being “outsiders” allowed them to challenge old assumptions. Unsurprisingly, they found that prior Western estimates had greatly exaggerated the size of communist forces. Specifically, they found that Soviet divisions were about one third as large as American divisions. Thus, it made little sense to simply compare the respective number of divisions. They also found that many of the supposed 175 Soviet combat divisions were little more than understrength and under-resourced cadre divisions or reserve units that existed at an even lower state of readiness than U.S. reserve and National Guard units. In short, the U.S. was comparing just its combat divisions with the entirety of the Red Army. But even this miscalculation understates the inaccuracy of early estimates because analysts also failed to acknowledge the greater firepower of U.S. units, which gave NATO forces an even larger qualitative edge.
Similar measurement problems were present in air power estimates. For example, a joint U.S. Air Force-Luftwaffe study concluded that the Warsaw Pact possessed both a quantitative and qualitative advantage in aircraft, allowing them to achieve complete air superiority in only three days. An incredulous McNamara again turned to independent sources of analysis to review these projections. Systems Analysis found that the study’s estimates compared the entire Soviet Air Force with American planes specifically designated for use in a NATO contingency. Moreover, the study assumed that Moscow could reinforce continuously while strictly limiting U.S. aircraft reinforcement rates. When these errors were corrected, it was revealed that NATO actually had more aircraft both in theater and in total than the Warsaw Pact. Further analysis also revealed that the more expensive NATO aircraft were qualitatively superior across a range of measures, especially given their greater mission flexibility and longer loiter times. Even the most conservative estimates assessed each NATO aircraft to be worth two Soviet aircraft.
These revised findings in relative strength of conventional forces did not necessarily imply that NATO could defeat the Warsaw Pact – the conventional balance was still relatively tight, and the outcome of a conflict might go either way depending on several assumptions and the quality of leadership on either side. However, these improved assessments suggested that NATO had more than a fighting chance at successfully defeating communist forces without the imperative of resorting to nuclear weapons. The obvious implication of this realization was that rather than fatalistically abandoning conventional preparation as simply irrelevant, the U.S. and NATO needed to carefully prepare for a conventional showdown in Central Europe. Moreover, these revised estimates suggested that a shift away from an exclusively nuclear strategy was clearly tenable.
NATO never completely eliminated its reliance on nuclear weapons, of course. A secure arsenal of strategic weapons was crucial for ensuring nuclear deterrence, and tactical nuclear weapons served several purposes including signaling support to European allies and deterring the use of Soviet low-yield nuclear devices. Moreover, the “flexible” component of flexible response was never fully realized for reasons explained above. Instead, forces remained largely concentrated in Europe and Asia instead of being based in the continental U.S.
Nevertheless, the shift to a more conventionally-focused strategy did occur. Pressure for change initially resulted from growing Soviet nuclear stockpiles that rendered American nuclear threats largely moot as a function of the potential for Soviet nuclear retaliation. This led to a push toward a more flexible conventional posture that could both deter general war and respond to regional contingencies like Korea. The effectiveness of this strategy was initially in doubt given assumptions of overwhelming Soviet conventional superiority, but a push for more careful assessments and the growth of new independent sources of analysis at least partially removed from the parochial interests of the services led much of the conventional wisdom regarding Soviet forces to be overturned. With the growth of the Soviet nuclear arsenal pushing the U.S. away from massive retaliation and improved intelligence suggesting the viability of a strategy based around conventional forces, it became increasingly obvious that “flexible response” was a superior strategy.
 Steven Ross, American War Plans 1945-1950 (London: Frank Cass, 1988), 53.
 Ibid., 59, 61.
 “National Security Council Report, NSC 68, ‘United States Objectives and Programs for National Security’,” April 14, 1950, National Archives, 16 and 18.
 Peter Grier, “The First Offset,” Air Force Magazine, June 2016, 57.
 Alain Enthoven and K. Wayne Smith, How Much is Enough (New York, N.Y.: Harper and Row, 1971), 119.
 Quoted in How Much is Enough, 122.
 NSC-68, 20.
 Ibid., 54-56.
 David Alan Rosenburg, “U.S. Nuclear Warplanning, 1945-1960,” in Strategic Nuclear Targeting, Desmond Ball and Jeffery Richelson eds. (Ithaca, N.Y.: Cornell University Press, 1986), 46-47.
 For example, there was significant bureaucratic infighting and inter-service disagreement about SAC’s autonomy and independence (Ibid., 45-46).
 Grier, 59-60.
 Enthoven and Smith, 123.
 NSC-68, 5 and 7.
 William Kaufman, Planning Conventional Forces 1950-1980 (Washington, D.C.: Brookings Institution, 1982), 4.
 Maxwell Taylor, “Flexible Response-A New National Military Program,” in American Defense Policy, Richard Head and Ervin Rokke, ed. (Baltimore, Md.: Johns Hopkins University Press, 1973), 205.
 Kaufman, 5-7.
 Ibid., 17-19.
 Enthoven and Smith, 125.
 Ibid., 132-134.
 Ibid., 134.
 Ibid., 142.
 Ibid., 138-139.
 Ibid., 136.
 Ibid., 136-137.
 Ibid., 144.
 Ibid., 145.
 Ibid., 145-146.
 Taylor notes that ensuring an effective strategic nuclear deterrent was the greatest military imperative. See esp. p. 205.
 Enthoven and Smith, 123.