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Ambiguity about whether a weapon is nuclear-armed prior to its launch is an underappreciated, serious, and growing danger. Rising geopolitical tensions and the decay of arms control are exacerbating the risk that such pre-launch warhead ambiguity could lead to nuclear use in a crisis or conflict. Recent developments in technology—as well as potential future advances, such as the development of ambiguous intercontinental missiles—further add to the danger.

A first step toward reducing these risks is to enhance awareness among decisionmakers of the causes and potential consequences of ambiguity. Unilateral and cooperative risk-mitigation measures could further reduce the danger of escalation, including in conflicts between the United States and Russia or the United States and China.

Basic concepts. As a result of warhead ambiguity, one state may mischaracterize an adversary’s weapons—that is, wrongly assess how they are armed—or be unable to characterize them. Mischaracterization can lead to a false positive (misidentifying a nonnuclear weapon as a nuclear one) or a false negative (misidentifying a nuclear weapon as a nonnuclear one). If mischaracterization or uncertain characterization is unintended, then any resulting escalation can be classified as inadvertent.

An overlooked danger. To date, the debate about warhead ambiguity has mostly focused on the risk of a nonnuclear weapon being mistaken for a nuclear weapon after launch. Pre-launch dangers, especially those arising from false positives, have attracted much less attention. Mischaracterization and uncertainty prior to launch, however, have occurred frequently throughout the nuclear age. Moreover, the escalation risks associated with pre-launch ambiguity could be more serious than the post-launch risks for three reasons. First, pre-launch ambiguity could persist over a much longer time window, thus allowing states to exercise options that they would not have time to implement between the launch of an adversary’s weapons and their detonation. Second, false negatives could not increase escalation risks after launch, but they could do so beforehand. Third, post-launch ambiguity could only spark escalation in a conflict involving the United States or Russia because they are the only states capable of initiating a nuclear response prior to the detonation of incoming weapons. By contrast, pre-launch ambiguity could lead to escalation in crises and conflicts involving other states.

James M. Acton
Acton holds the Jessica T. Mathews Chair and is co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace.
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Technology and ambiguity. The likelihood of mischaracterization or uncertainty about how a weapon is armed is greatest for ambiguous delivery systems—that is, superficially similar nuclear and nonnuclear delivery systems and dual-use delivery systems (for which both nuclear and conventional warheads are available and which can carry either). Ambiguous aircraft and ground-launched cruise and ballistic missiles are most salient to an analysis of the risks of pre-launch ambiguity.

China, Russia, and the United States, which are the focus of this report, all deploy ambiguous delivery systems; and all Chinese, Russian, and U.S. aircraft with a nuclear mission are dual-use. China and Russia deploy ambiguous ground-launched ballistic missiles, while Russia also fields dual-use ground-launched cruise missiles. The United States, meanwhile, is seeking to reacquire a nuclear-armed sea-launched cruise missile, which, even if it is not dual-use, will likely reintroduce ambiguity to U.S. naval forces by being deployed on a platform that does not currently carry nuclear weapons.

The significance of ambiguous delivery systems is set to increase even further. Technological developments could permit China and Russia, in particular, to deploy more accurate ambiguous ground-launched missiles of progressively longer ranges—especially in Russia’s case, now that the 1987 Intermediate-Range Nuclear Forces Treaty has collapsed.

Causes of mischaracterization or uncertainty. Incorrect or uncertain conclusions about how an ambiguous delivery system is armed can result from intelligence analysts’ misinterpretation of the imperfect information available to them. Equally likely to generate false positives or false negatives, this misinterpretation can have various causes:

  • Assessments about whether a delivery system has a nuclear role, a conventional role, or both may be incorrect or uncertain. Recent public U.S. assessments, for example, indicate uncertainty about whether nuclear warheads are available for certain foreign delivery systems that clearly have a nonnuclear role.
  • Distinguishing between superficially similar nuclear and nonnuclear weapons can be difficult. The United States, for instance, faced this challenge when the Soviet Union sold ambiguous MiG-23 aircraft to Cuba in the late 1970s.
  • Analysts may misjudge, or have insufficient information to judge, what types of warheads are loaded onto or available for dual-use systems—a challenge that currently faces the North Atlantic Treaty Organization in characterizing Russian forces deployed in Kaliningrad.

Deployment patterns and practices can make it even more difficult to characterize ambiguous delivery systems, particularly when both nuclear and nonnuclear versions of the same system are deployed simultaneously. For example, in the run-up to the Cuban Missile Crisis, the Soviet Union shipped nuclear and conventional cruise missiles to Cuba, but the U.S. Central Intelligence Agency failed to identify the difference and assessed them all to be conventionally armed.

All dual-use U.S. aircraft are available for both nuclear and nonnuclear operations; they are not grouped, geographically or organizationally, according to function. Likewise, Russia appears to group few, if any, of its ambiguous aircraft and ground-launched missiles functionally. In the fog of a crisis or conflict, the entanglement of nuclear and nonnuclear delivery systems being operated side by side could pose a further challenge to characterization.

China, by contrast, appears to operate geographically and organizationally distinct launch brigades for nuclear and conventional missiles (although internal pressures to end this practice may be growing). However, the deployment areas for nuclear and nonnuclear variants of the same missile may overlap, potentially leading to intermingling and hence greater characterization challenges in a crisis or conflict. Moreover, in a crisis or conflict, China’s efforts to obscure its missile operations might add to the difficulty by hampering the United States’ ability to track Chinese missiles after leaving their garrisons.

If intelligence analysts cannot draw firm conclusions about how ambiguous delivery systems are armed, national and military leaders may assume, for both military and psychological reasons, that those weapons are loaded with nuclear warheads—potentially yielding false positives. For example, during the Cuban Missile Crisis, when confronted with multiple deployments of ambiguous Soviet systems, U.S. decisionmakers assumed that two types of aircraft were nuclear-armed, even though there was little direct evidence to support their conclusion.

Escalation risks. Mischaracterization, unlike uncertainty, could increase the risks of inadvertent escalation for two reasons. First, warhead ambiguity could obfuscate signaling operations and increase the already significant challenges of communicating and assessing intent.

  • False negatives could lead to an intended nuclear signal being missed, potentially prompting the signaler to further escalate the crisis or conflict because it concluded its message had been ignored. Historically, nuclear signals have been missed even without the complications introduced by warhead ambiguity. In theory, states could clarify the meaning of signaling operations involving ambiguous delivery systems by, for instance, issuing public or private statements or threats. In reality, however, such measures would come with downsides and might not be implemented fully or even at all.
  • False positives, meanwhile, could lead a state to conclude incorrectly that its adversary was issuing a nuclear signal or undertaking clandestine preparations for nuclear use. While such a misinterpretation could unintentionally lead to deescalation, it would more likely catalyze an escalation spiral. Historically, nuclear operations and threats have led to reciprocal escalation, even if the resulting spirals ended short of nuclear use. For example, during the 1973 Yom Kippur War, the United States’ incorrect belief that Soviet nuclear warheads were being transported to Egypt helped spark a U.S. nuclear alert, which may, in turn, have prompted the start of a Soviet alert.

Second, in any crisis or conflict, each adversary would devote significant resources to collecting intelligence about the other’s military capabilities. However, by degrading the quality of intelligence information, warhead ambiguity—especially if it resulted in false negatives—could increase the likelihood of a state’s initiating a potentially escalatory military operation because it had underestimated the dangers of doing so.

Recommendations. However desirable it might be for nuclear-armed states to reassess their reliance on ambiguous delivery systems, they are highly unlikely to do so for strategic, financial, psychological, and organizational reasons. Less ambitious unilateral and cooperative risk-reduction measures may be more feasible. The following proposals are framed as actions for the United States to consider and adopt. But risk mitigation should be a shared responsibility, and Beijing and Moscow have an obligation to engage constructively with any good-faith proposals Washington offers and, in parallel, develop their own unilateral risk-reduction measures. The United States, meanwhile, has an obligation to seriously consider how it could address Chinese and Russian concerns about the survivability of their nuclear forces, which should help increase Moscow’s and Beijing’s interest in cooperative risk reduction.

Exercise Restraint in Acquisitions

  • The U.S. secretary of defense should require relevant Department of Defense decisionmakers to consider any potential escalation risks resulting from warhead ambiguity when deciding whether to acquire new categories of ambiguous weapons. To this end, those decisionmakers should be presented with a formal assessment of such risks.
  • The United States should propose to China and Russia that they jointly agree not to acquire ambiguous intercontinental ballistic, cruise, or hypersonic boost-glide missiles.

Be Transparent About Capabilities

  • The United States should propose to China and Russia that they declare, publicly or privately, each type of missile and aircraft that they deploy as nuclear-armed, conventionally armed, or dual-use.
  • The United States should propose to China and Russia that they privately discuss any observable differences in design or deployment patterns between their nuclear- and conventionally armed ambiguous weapons.

Improve Operational Planning

  • The U.S. Department of Defense and relevant combatant commands should plan for crises and conflicts on the assumption that each participant might mischaracterize or be unable to characterize the other’s ambiguous weapons.
  • The U.S. secretary of defense should require relevant decisionmakers to consider any potential escalation risks resulting from warhead ambiguity when deciding whether to authorize strikes with or against ambiguous delivery systems. To this end, those decisionmakers should be presented with a formal assessment of such risks.
  • U.S. military planners and decisionmakers should be aware of the trade-offs associated with using ambiguous delivery systems for signaling operations.
  • If the United States uses ambiguous delivery systems for nuclear signaling, it should take steps to mitigate the risks associated with warhead ambiguity by, for example, clarifying the meaning of the signal in an accompanying statement.

The United States should offer verbal assurances to reduce the likelihood of false positives resulting from operations involving conventionally armed ambiguous weapons.


This work was made possible by a generous grant from the John D. and Catherine T. MacArthur Foundation. It benefited enormously from the extraordinary research skills of Nicholas Blanchette, Gaurav Kalwani, Valeriia Lozova, Kayla Matteucci, and Thu-An Pham. I am also indebted to Carnegie’s outstanding communications department—in particular, Lori Merritt and Jocelyn Soly—for their excellent work in editing, design, and production. Finally, for their insightful conversations and/or trenchant critiques of earlier drafts, I would like to thank William J. Burns, Thomas Carothers, Toby Dalton, Scott LaFoy, George Perkovich, Pavel Podvig, Joshua H. Pollack, Jen Psaki, Vince Manzo, Vipin Narang, Nicholas Wright, and members of Carnegie’s Nuclear Policy Program. However, I am solely responsible for this report’s contents.


CIA: Central Intelligence Agency

ICBM: Intercontinental ballistic missile

INF Treaty: Intermediate-Range Nuclear Forces Treaty

IRBM: Intermediate-range ballistic missile

ISR: Intelligence, surveillance, and reconnaissance

KPA: Korean People’s Army

NATO: North Atlantic Treaty Organization

PLA: People’s Liberation Army

SLBM: Sea-launched ballistic missile

SSBN: Ballistic missile submarine