▶ The heyday of nuclear sharing in NATO was the late 1950s, when the United States took substantive steps to ensure that core European allies would be able to access and employ U.S.-made nuclear weapons without direct authorization from Washington.

▶  Such arrangements were drastically curtailed in the early 1960s; NATO today practices what might properly be called a non-substantive or “vestigial” form of nuclear sharing.

▶  Proposals to import “NATO-like” nuclear sharing arrangements to the ROK-U.S. alliance today typically betray confusion and ignorance about these basic facts.

Proponents of new nuclear ideas are having quite a moment in South Korea. One such idea they throw around with uncanny frequency involves the concept of “nuclear sharing.” Both policy analysts and presidential candidates have expressed support for adopting “NATO-like” nuclear sharing arrangements to bolster the Republic of Korea (ROK)-U.S. alliance’s deterrent posture against growing regional threats. And recently, the ROK Office of the President was apparently so eager to describe alliance’s highly publicized April 2023 “Washington Declaration” as signaling “de facto nuclear sharing” that it prompted an immediate dismissive response from the U.S. National Security Council.  

Given that nuclear sharing will probably continue to attract attention in South Korean national security debates, it is important for policymakers and concerned citizens alike to be clearly informed about what the concept has meant historically and what kind of arrangement it is today—hence the purpose of this brief contribution.

Nuclear Sharing Then and Now

As a recent article explains in detail, nuclear sharing denotes policies that grant nominally non-nuclear allies significant roles in the management and employment of a nuclear-armed leading power’s nuclear capabilities. The goal is to improve the alliance’s ability to deter aggression on the non-nuclear ally by transferring the anticipated locus of nuclear escalation decisions to the ally’s territory. In the heyday of nuclear sharing in the North Atlantic Treaty Organization (NATO), that is, the second half of the 1950s, the United States took significant steps to make this a reality in Europe. Among other things, it contrived astonishingly loose custodial arrangements to ensure that the military forces of core allies like France and West Germany would have reliable access to U.S.-made nuclear weapons during times of severe military crisis. As President Dwight D. Eisenhower acknowledged, the goal was to “give, to all intents and purposes, control of [American nuclear] weapons’ to the Europeans; the U.S. was to “retain titular possession only.” This was deemed especially necessary given that the NATO allies confronted a conventionally preponderant adversary—the Soviet Union—in a critical theater of military operations.

But beginning in the early 1960s, the John F. Kennedy administration’s introduction of procedural and technical mechanisms (e.g., Permissive Action Links [PALs]) designed to prevent allied forces from employing nuclear weapons without U.S. authorization, along with the broader elevation of nuclear nonproliferation as a core priority of U.S. foreign policy, spelled the end of substantive nuclear sharing in NATO. Since 1962—when U.S. theater nuclear weapons were first fitted with PALs—NATO has practiced a non-substantive or “vestigial” form of nuclear sharing that, for all intents and purposes, is an institutional façade meant to make America’s nuclear monopoly in NATO more politically palatable for its European allies.

The fact that NATO’s post-1962 “nuclear sharing” arrangements can be properly described as “non-substantive” or “vestigial” becomes clear by examining their key characteristics as described by knowledgeable individuals and contrasting them with the substantive nuclear sharing policies of the late 1950s. NATO’s official factsheet on its contemporary nuclear sharing policies emphasizes that while allied dual-capable aircraft (DCA) could deliver nuclear weapons in the event NATO conducts a nuclear mission, such a “nuclear mission can only be undertaken after explicit political approval” by the national authorities of nuclear weapons states. It is thus clarified that “NATO’s nuclear sharing is the sharing of the Alliance’s nuclear deterrence mission” should it be undertaken—“It is not the sharing of nuclear weapons.” U.S. policymakers likewise acknowledge that “nuclear sharing” in 21st-century NATO exists within a broader web of institutions designed to centralize nuclear weapons and decision-making abilities in Washington’s hands. As former U.S. Deputy Assistant Secretary of Defense for Nuclear and Missile Defense Policy Brad Roberts writes, America’s NATO allies participate in nuclear planning and training but “U.S. nuclear weapons may be employed only on the order of the president of the United States.”

“Nuclear sharing” in NATO after 1962, then, serves grand strategic objectives diametrically opposed to those that the United States pursued during the heyday of nuclear sharing in the late 1950s. Nuclear sharing during this brief period was pursued as a means to devolve substantive nuclear assets and decision-making authorities to allies rather than to centralize them in the hands of the United States. In an important sense, this strategy was motivated by the logic of nuclear deterrence itself. As Thomas Schelling observed in his all-important book Arms and Influence, deterring powerful adversaries who themselves possess nuclear weapons with the threat of nuclear escalation does not—and indeed cannot—depend on the “threat to launch a disastrous war coolly and deliberately[.]” It instead relies on the threat that the deterring state’s leaders might “stumble into a war” regardless of their wishes (pp. 97-98). Thus, the core idea of nuclear sharing—“suggestions that nuclear weapons should be put directly at the disposal of German troops”—was that “the Germans would be less reluctant to use them—and that Soviet leaders know they would be less reluctant—than their American colleagues in the early stages of war or ambiguous aggression [in Europe]” (p. 38). The point was to increase the likelihood that the alliance might “stumble into” a nuclear war despite the faraway leading power’s reluctance because real nuclear assets and decision-making authorities were dispersed in the hands of local allies. This was understood by policymakers and experts alike in the heyday of nuclear sharing. It was clear that the United States “want[ed] to disperse the power to decide to use nuclear weapons,” Albert Wohlstetter observed at the time—“to have more than one center for such decision in the West.”

Today, scholars who are well-versed on the subject typically dismiss the security value of “NATO-like” nuclear sharing precisely because it offers no clear mechanism by which allied territory can become the locus of nuclear escalation decisions. Political scientists Jennifer Lind and Daryl Press, for example, point out that “the weapons [are] still…firmly in the control of American leaders” under present-day nuclear sharing arrangements, which makes nuclear deterrence “no more credible” than if such arrangements were not in place. While this is entirely correct, it simply underscores the point that the United States has not practiced true nuclear sharing in NATO since the early 1960s.

Why did “Nuclear Sharing” in NATO Endure after the 1950s?

A question then arises: if it is so militarily vacuous, why has the United States practiced non-substantive nuclear sharing in NATO at all since the early 1960s? The simplest explanation is path dependency. As historian Marc Trachtenberg has documented, the Kennedy administration wished to avoid upsetting the allies by being too brazen about overhauling U.S. policies away from substantive nuclear sharing. Given the salience that the idea of nuclear sharing had occupied in U.S. grand strategy in the 1950s and the lengths to which American leaders had gone to assure key allies that their forces would have immediate and effective control over nuclear weapons in times of crisis under this arrangement, it would not have been politically prudent for Washington to present its centralizing efforts as a radical change in basic situation—even though they in fact were.

Euphemisms thus became part and parcel to the conduct of U.S. nuclear strategy. For example, the introduction of PALs—technical mechanisms designed to foreclose any possibility that local military actors might launch nuclear weapons without direct authorization from Washington—was described as one of many steps to “improve command and control.” A forum where U.S. officials would “educate” the allies about nuclear policies singularly crafted and executed by Washington was designated the “Nuclear Planning Group.”

In short, starting in the early 1960s, the United States pursued systematic efforts to preserve the semblance of “nuclear sharing” in NATO—a strategy originally conceived to give key allies a real ability to decide on nuclear escalation in desperate times—while vitiating its substance. The “nuclear sharing” arrangements that are in place today are vestiges of these efforts.

Nuclear (Sharing) Myths, Political Realities

This leads to the final important question: in light of these facts, what are we to make of contemporary proposals to import “NATO-like” nuclear sharing arrangements to shore up deterrence for America’s core allies in East Asia? To the extent that these proposals have NATO’s present-day nuclear sharing arrangements in mind, they appear to rest more on confusion and ignorance about the core logic of nuclear sharing than anything else. Nuclear sharing that has any substantive significance must meaningfully increase the risk of inadvertent, unauthorized nuclear escalation by dispersing nuclear capabilities in allied hands. Indeed, those who understand the logic of nuclear deterrence theory should understand that “improving” the credibility of extended nuclear deterrent threats depends on the manipulation of such risks. Any “nuclear sharing” arrangement that does not give local military actors—field commanders and allied forces—a real ability to decide on nuclear escalation during times of crises without “a political decision from far away” is nuclear sharing in name only. Confusion and ignorance about these key facts go a long way toward explaining most calls for “NATO-like” nuclear sharing by policymakers and pundits today. This is consistent with important works which have observed that the logics undergirding nuclear deterrence theory might be too intricate and counterintuitive for non-specialists to fully grasp.

More puzzling is when individuals who have recognized expertise on nuclear deterrence occasionally join these voices. A recent essay in a prominent expert outlet, for instance, argues that “[t]o shore up extended deterrence, the United States could pursue bilateral nuclear sharing and planning arrangements with Japan and South Korea” despite acknowledging that “[t]he United States would retain sole custody of nuclear weapons and possess final authority on their release and use.” Another expert essay likewise argues that the United States should explore “Korean and Japanese receptivity toward the wartime sharing of nuclear weapons (under U.S. control and within NPT limits)” as a means “to address its allies’ nuclear insecurities.” Trained security scholars who endorse such proposals must identify the mechanisms by which non-substantive nuclear sharing is supposed to “shore up extended deterrence” or redress allied “nuclear insecurities” despite the qualification of absolute U.S. control over the weapons. I do not believe this is possible.