Table of Contents

If warhead ambiguity leads to mischaracterization (as opposed to uncertainty), four different scenarios can arise, depending on when the mischaracterization occurs (pre- or post-launch) and whether it is a false positive or a false negative (see table 1).

So far, debates about the risks of ambiguous delivery systems have focused, almost exclusively, on just one scenario: a nonnuclear weapon’s being mistaken for a nuclear weapon after it has been launched. This focus is not surprising, given concerns that the target state might launch an immediate nuclear counterstrike. Yet, while the consequences of post-launch warhead ambiguity could be extremely high, assessing the likelihood of this worst-case scenario has proved contentious, leading to a somewhat rancorous and ultimately static debate.1 Optimists argue that even if Russia, say, mischaracterized a small incoming conventional attack as nuclear, it would have no rational reason to launch an immediate response since its nuclear deterrent would not be in jeopardy. Pessimists argue that Russia might interpret a limited strike as the prelude to a large-scale attack and that even a small likelihood of escalation should be unacceptable because of the severity of the potential consequences.

In one way, pre-launch and post-launch ambiguity are closely connected: If a state mischaracterizes a weapon before launch, it will likely continue to do so afterward. Accordingly, understanding the likelihood of pre-launch ambiguity may help to shed light on the magnitude of the post-launch risks.

Yet, while the debate about post-launch ambiguity has been raging, potential causes, types, risks, and consequences of pre-launch ambiguity have been largely ignored. The only pre-launch scenario that has attracted significant attention is the risk of the United States’ attacking ambiguous Chinese ballistic missiles that it believed were conventional but were actually nuclear-armed.2 In this case, China might conclude that its nuclear deterrent was under threat and therefore feel use-or-lose pressures that could precipitate escalation. This scenario, which involves a false negative, is indeed an important one, but concerns about the survivability of a nuclear arsenal are not the only potential cause of escalatory pressures. A state could also overestimate or underestimate its opponent’s willingness to resort to nuclear use or misread that opponent’s capabilities. False positives, as well as false negatives, could cause these kinds of misperceptions.

Moreover, pre-launch operations involving ambiguous dual-use aircraft, as well as ground-launched missiles, could spark escalation, which could feasibly occur in a U.S.-Russian or U.S.-Chinese contingency. In fact, the risks might be greater in a U.S.-Russian scenario given that Russia fields many more types of ambiguous delivery systems than either the United States or China.

Pre-launch ambiguity probably creates greater escalation risks than post-launch ambiguity for at least three reasons. First, pre-launch ambiguity could persist over a much longer time window. In a post-launch scenario, if a state were to misidentify one or more incoming nonnuclear weapons as nuclear, its leadership would face an essentially binary choice in the minutes before impact was expected: do nothing or launch a nuclear response.3 The likelihood of a nuclear response would probably be small, not least because of the technical difficulty of responding so quickly (though, as noted above, analysts disagree about precisely how small it would be and how small it should be for the risks of the incoming attack to be tolerable).

Yet, in a pre-launch scenario, the ambiguity could persist for much longer—weeks conceivably—and therefore allow the targeted state to consider a greater range of responses. Precisely because many of these options would be less extreme than nuclear use, the state would be more likely to take some kind of action.

Second, while false negatives could not increase escalation risks after a weapon’s launch, they could do so beforehand. Before launch, false negatives could trigger escalation by, for example, frustrating attempts at nuclear signaling. After launch, a false negative could occur and further escalation would be likely.4 However, the cause of such escalation would be a nuclear attack against a nuclear-armed state; the target’s incorrect assessment, prior to detonation, that the attack was nonnuclear would be unlikely to add much to the danger.

While the debate about post-launch ambiguity has been raging, potential causes, types, and consequences of pre-launch ambiguity have been largely ignored.

Third, pre-launch ambiguity could be escalatory in more contexts than post-launch ambiguity. Russia and the United States are the only nuclear-armed states that have the equipment and procedures necessary for enabling their leaders to order a nuclear counterstrike before incoming warheads have detonated, though China may be moving in this direction.5 Post-launch ambiguity, therefore, could spark escalation only in a conflict involving the United States or Russia.6 By contrast, before launch, ambiguous delivery systems deployed for prolonged periods may be detectable with even the relatively basic intelligence, surveillance, and reconnaissance (ISR) technologies that are accessible to all nuclear-armed states.7 North Korea, for example, has air-defense radars that can detect U.S. dual-use aircraft on its periphery (especially if the United States wants them to be detected for signaling purposes). Thus, even though this report focuses on potential U.S.-Russian and U.S.-Chinese conflicts, the risks of escalation exist in other contexts, too—in particular, conflicts involving India and Pakistan, North Korea and the United States, or Russia and France, most likely fighting as part of the North Atlantic Treaty Organization (NATO).


1 See, for example, Costlow, “The New Nuclear Cruise Missile and the Stability Argument”; Perry and Weber, “Mr. President, Kill the New Cruise Missile”; James M. Acton, Silver Bullet? Asking the Right Questions About Conventional Prompt Global Strike (Washington, DC: Carnegie Endowment for International Peace, 2013), 113–118,; Payne et al., Conventional Prompt Global Strike, 38–48; M. Elaine Bunn and Vincent A. Manzo, Conventional Prompt Global Strike: Strategic Asset or Unusable Liability? Strategic Forum 263 (Institute for National Security Studies, National Defense University, February 2011), 14–17,; Bruce M. Sugden, “Speed Kills: Analyzing the Deployment of Conventional Ballistic Missiles,” International Security 34, no. 1 (Summer 2009): 141–144; Joshua Pollack, “Evaluating Conventional Prompt Global Strike,” Bulletin of the Atomic Scientists 65, no. 1 (January/February 2009): 18–19; Committee on Conventional Prompt Global Strike Capability, Naval Studies Board, and Division on Engineering and Physical Sciences, National Research Council of the National Academies, U.S. Conventional Prompt Global Strike: Issues for 2008 and Beyond (Washington, DC: National Academies Press, 2008), 71–77,; Postol, “An Evaluation of the Capabilities and Limitations of Non-Nuclear-Armed Trident Ballistic Missiles for Short-Time Conventional Strikes,” 10–11 and 14–43; and Pavel Podvig, Russia and the Prompt Global Strike Plan, PONARS Policy Memo 417 (December 2006), 2,

2 Caitlin Talmadge, “Would China Go Nuclear? Assessing the Risk of Chinese Nuclear Escalation in a Conventional War With the United States,” International Security 41, no. 4 (Spring 2017): 73–75 and 84–90; and Wu Riqiang, Sino-U.S. Inadvertent Escalation (Program on Strategic Stability Evaluation, Georgia Institute of Technology), 5–6 and 7–8,

3 The state could also try to intercept the attack, but the authority to do so would most likely have to be predelegated to lower-level commanders directly responsible for air- and missile-defense operations.

4 Indeed, whatever Japanese air-defense forces were present around Hiroshima on August 6, 1945, presumably failed to realize that the Enola Gay was carrying a nuclear warhead. This ambiguity was not just the result of Japan’s lack of awareness of the atomic bomb’s existence. Prior to the attack, small unescorted groups of B-29 bombers flew high-altitude practice runs over Japan, partly to “accustom” it to such operations (for many months previously, conventional bombing raids had been undertaken at low altitude by large escorted groups). Richard Rhodes, The Making of the Atomic Bomb (New York: Simon & Schuster, 1986), 687.

5 Gregory Kulacki, The Chinese Military Updates China’s Nuclear Strategy (Cambridge, MA: Union of Concerned Scientists, March 2015), 4,

6 In fact, ambiguity could likely only precipitate escalation in a conflict involving both states.

7 Mischaracterization may be more likely to result from ISR assets with less ability to detect subtle differences between nuclear- and conventionally armed delivery systems.