Not all ambiguous delivery systems are relevant to pre-launch warhead ambiguity. In fact, some of the weapon types most discussed in relation to post-launch ambiguity—air-launched cruise missiles, in particular—are largely irrelevant to pre-launch ambiguity because they are difficult to observe directly at that point. But the ambiguous platforms that carry them may be visible. Aircraft and ground-launched cruise and ballistic missiles, therefore, are most salient to an analysis of the risks of pre-launch ambiguity.
Pre-launch ambiguity can also be associated with surface ships and, if they can be tracked, submarines. This report’s scope does not permit detailed consideration of naval platforms, which have very different operational practices from those of aircraft and ground-launched missiles. Note, however, that if a single ship or submarine is used to carry both nuclear and conventional weapons, acute and probably irresolvable ambiguity could result.
Neither the People’s Liberation Army (PLA) Navy nor the U.S. Navy currently deploys vessels that carry both nuclear and nonnuclear weapons (except for the nonnuclear torpedoes that U.S. and presumably Chinese ballistic missile submarines [SSBNs] carry for self-defense).1 By contrast, the Russian Navy deploys nuclear- and conventionally armed cruise missiles on attack submarines and a range of nuclear and nonnuclear weapons on surface ships.2 Reflecting the ambiguity inherent in this posture, the U.S. Defense Intelligence Agency stated, in 2017, that Russia’s “Baltic fleet presents a significant long-range precision conventional and theater nuclear strike threat to Western Europe.”3 (There is no technical reason why a single aircraft or multiple-warhead missile could not carry both nuclear and nonnuclear munitions, as Russian ships do, but none appear to have been used in this way, with the exception of conventional armaments on nuclear-armed aircraft for self-defense.)
Dual-use aircraft are as old as the nuclear age. The first nuclear-weapon delivery system—the B-29 bomber, which was used to drop nuclear weapons on Hiroshima and Nagasaki in World War II—was designed and originally used exclusively for carrying conventional bombs. Today, all U.S. aircraft qualified to deliver nuclear weapons are also assigned a conventional role, as are all the NATO aircraft with a role in delivering U.S. nuclear weapons (see table 2).4 (In fact, the B-58, retired in 1970, appears to be the only U.S. aircraft that never had a conventional role.)5
Similarly, no contemporary Russian aircraft are used exclusively for nuclear operations.7 While dual-use Russian aircraft have long been armed with cruise missiles or gravity bombs, Russia has recently developed an air-launched IRBM, Kinzhal, that Russian President Vladimir Putin has stated can carry a nuclear or nonnuclear warhead.8
Prior to China’s acquisition of a substantial ballistic missile force in the 1970s, the United States believed that Beijing’s primary delivery system for nuclear weapons was dual-use aircraft—initially the Soviet-produced Tu-16 and subsequently the Chinese-manufactured H-6. These were probably the only Chinese aircraft to have ever been assigned a nuclear role.9 Once China had built up its missile forces, that role became marginal and perhaps even nonexistent. According to a 2019 Pentagon assessment, however, “[s]ince at least 2016, Chinese media have been referring to the H-6K [the latest H-6 variant] as a dual nuclear-conventional bomber,” suggesting that this aircraft’s nuclear role may have been revived.10
Ambiguous ground-launched ballistic and cruise missiles represent a more dynamic area of technology. The history of these missiles is instructive because it suggests what their future may be. Such missiles were relatively unimportant throughout much of the Cold War—first because of technological limitations and later because of treaty limitations. As these limitations have progressively been lifted, and as China has emerged as a strategic competitor to the United States, the capabilities and importance of ambiguous Chinese and Russian ground-launched cruise and ballistic missiles have increased. This trend appears set to continue.
Starting in the mid-1950s, the Soviet Union and the United States deployed dual-use ground-launched ballistic missiles with ranges of up to a few hundred kilometers (see figure 1). Given accuracy limitations, however, the military utility of early ballistic missiles armed with high explosive warheads would have been marginal at best. For example, the accuracy of the Soviet SS-1B missile was estimated in a 1961 U.S. National Intelligence Estimate to be 900 meters (0.6 miles).11 To put this figure in context, if such a missile were fired against a building the size of the Pentagon—a huge facility by the standards of military targets—the probability of a direct hit would be a mere 5 percent or so.12 Moreover, the accuracy of ballistic missiles degrades as their range increases. For this reason, weapons with ranges beyond a few hundred kilometers were exclusively nuclear-armed early in the Cold War.13
In the 1970s and 1980s, the Soviet Union and the United States capitalized on improved technology to deploy more accurate dual-use ballistic missiles. These weapons included the Soviet SS-12 Mod 2, which was first deployed in about 1984 and had a range of 900 kilometers (560 miles), making it the longest-range dual-use missile from the Cold War.14 The United States did not deploy a dual-use missile with a range beyond a few hundred kilometers, but, in the late 1970s, it seriously considered doing so.15
It is not difficult to imagine that, as the 1980s had progressed, Moscow and Washington could have deployed dual-use ground-launched ballistic missiles of increasingly long ranges. Moreover, during the same time period, cruise missiles were becoming more accurate and hence able to deliver nonnuclear warheads effectively, potentially enabling deployments of dual-use ground-launched cruise missiles. Both developments were forestalled by the INF Treaty, which prohibited all ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers (310 to 3,400 miles). Although the treaty was negotiated to rein in nuclear capabilities, its limits also applied to conventionally armed missiles and led to the elimination of SS-12 Mod 2 missiles, among others. Moreover, two years later, the Cold War ended and the United States stepped away from dual-use ballistic missiles entirely, dismantling the Lance missile even though it was not legally required to do so.
China, however, was not a party to the INF Treaty and has invested heavily in ambiguous missiles.
China, however, was not a party to the INF Treaty and has invested heavily in ambiguous missiles. It currently fields two nuclear-armed variants and two conventionally armed variants of its medium-range DF-21 ballistic missile (see box 1).16 In addition, China has now deployed one or two true dual-use missiles. In 2016, it started to field the DF-26, an IRBM that authoritative Chinese sources, as well as the Pentagon, state can accommodate a nuclear or nonnuclear warhead.17 Then, in an October 2019 military parade, Beijing exhibited a ground-launched hypersonic boost-glide weapon, the DF-17, implying that it had already deployed this missile or would do so shortly. According to reliable media reporting, the U.S. intelligence community (or at least parts of it) assesses that the DF-17 is dual-use.18
Box 1: China’s Ambiguous DF-21 Missiles
China appears to deploy four versions of its DF-21 medium-range ballistic missile. Two variants, the land-attack DF-21C and antiship DF-21D, are conventionally armed. The other two are nuclear-armed: the DF-21A and a variant referenced by the U.S. Department of Defense as the CSS-5 Mod 6, whose Chinese designation is not yet publicly known (though it is sometimes listed as the DF-21E in nongovernmental English-language sources).19
The two conventional variants are very similar, if not identical, to one another but differ in several significant ways from the nuclear-armed DF-21A (see adjacent figure).20 Because these differences are observable in satellite imagery, U.S. analysts should have little difficulty distinguishing between DF-21A and DF-21C/D missiles, even if such missiles were collocated—assuming, that is, that U.S. ISR capabilities are functioning normally and that China has not engaged in deception.
Little is known publicly about the design of the nuclear-armed CSS-5 Mod 6, which was first deployed in about 2015 or 2016. But this weapon could have important implications for the risks of pre-launch warhead ambiguity.21 Specifically, if the missile and its TEL are similar or identical to the DF-21C/D and its TEL, then its deployment probably increases the likelihood of mischaracterization or uncertainty. If, however, this system is observably different from the DF-21 C/D, then its deployment probably does not exacerbate the escalation risks.
Russia, meanwhile, has continued to field and enhance a force of dual-use ground-launched missiles. This force is highly opaque (and the accounting provided in table 2 may well be incomplete or inaccurate). Most of these weapons have ranges of less than 500 kilometers (310 miles) and were, therefore, not limited by the INF Treaty. But the United States claims that a new ground-launched cruise missile, the SSC-8 (often referred to by its Russian designation of 9M729), is dual-use and has a range of “well over” 500 kilometers.22 Russian insistence that the missile is treaty-compliant, which seems implausible, did not stop the United States from withdrawing from the INF Treaty in 2019.
With the treaty’s collapse, both Moscow and Washington have indicated that they are now developing ground-launched missiles with ranges longer than 500 kilometers. Only Russia, however, is likely to deploy dual-use systems (the United States will almost certainly focus on conventional systems, not least because the politics of basing nuclear-armed mobile missiles on an ally’s territory would be fraught). Immediately after Washington gave notice of its withdrawal from the treaty, Moscow outlined, in general terms, its military response. Putin ordered the development of a ground-launched variant of the Kalibr sea-launched cruise missile—which is, in fact, precisely what the SSC-8 is believed to be—and a ground-launched, intermediate-range hypersonic weapon.23 Separately, Defense Minister Sergei Shoigu announced that Russia would also extend the ranges of other weapons under development.24 No details about any of these systems—including how they will be armed—have been released. But it seems likely that Russia will deploy ground-launched missiles of increasingly long ranges and that at least some of them will be dual-use.
Other possible developments are not directly related to the INF Treaty’s demise. The U.S. Department of Defense, for example, has indicated that it seeks to reacquire a nuclear-armed sea-launched cruise missile. Even if this weapon is not dual-use, its deployment will still reintroduce ambiguity to U.S. naval forces because it will almost certainly be deployed on platforms—attack submarines or surface ships—that do not currently carry nuclear weapons.
Russia and, less likely, the United States could also develop ambiguous intercontinental missiles; in particular, they could use a booster for an intercontinental ballistic missile (ICBM) or sea-launched ballistic missile (SLBM) to launch a maneuverable reentry vehicle—that is, one with the capability to steer after it reenters the atmosphere. Ambiguity could arise in two ways.25 The reentry vehicle itself could be dual-use, like the one on Russia’s Kinzhal missile.26 Alternatively, the reentry vehicle could carry only a nonnuclear warhead but be launched by an ICBM or SLBM that was also deployed with nuclear warheads. The administration of then president George W. Bush tried to pursue this approach with the Conventional Trident Modification, a program to replace some nuclear warheads on Trident D5 SLBMs with nonnuclear weapons (this effort was eventually abandoned after Congress declined to fund it, in part because of the risks associated with post-launch ambiguity).27
China may have similar ambitions. It could build upon its deployment of the DF-21, DF-26, and DF-17 missiles by fielding ambiguous missiles of even longer ranges, including perhaps intercontinental-class weapons. Meanwhile, over the next decade or so, China may significantly enhance its air force’s role in nuclear operations. It is developing a new stealth bomber, which Chinese sources indicate will be dual-use, and an air-launched ballistic missile, which the Pentagon assesses “may include a nuclear payload.”28
Finally, China, Russia, and the United States are not the only states to possess ambiguous weapons. Other nuclear-armed states do, too, and such weapons could create escalation pressures, particularly in a conflict between France (most likely fighting as a part of NATO) and Russia, or India and Pakistan, or North Korea and the United States (see appendix).
1 Prior to the Presidential Nuclear Initiatives of 1991 and 1992, U.S. ships and submarines carried both nuclear and conventional weapons, whereas PLA Navy forces have never done so. Arms Control Association, “The Presidential Nuclear Initiatives (PNIs) on Tactical Nuclear Weapons at a Glance,” July 2017, https://www.armscontrol.org/factsheets/pniglance.
2 Igor Sutyagin, Atomic Accounting: A New Estimate of Russia’s Non-Strategic Nuclear Forces, Occasional Paper (London: Royal United Services Institute, November 2012), 39–51, https://rusi.org/sites/default/files/201211_op_atomic_accounting.pdf. This posture appears to contravene Russian commitments made under the Presidential Nuclear Initiatives.
3 Defense Intelligence Agency, Russia Military Power: Building a Military to Support Great Power Aspirations, DIA-11-1704-161 (Defense Intelligence Agency, 2017), 68, https://www.dia.mil/Portals/27/Documents/News/Military%20Power%20Publications/Russia%20Military%20Power%20Report%202017.pdf.
4 In theory, an aircraft that was assigned exclusively to nonnuclear operations could be converted to carry nuclear munitions (or vice versa). However, a meaningful distinction can be drawn between this kind of inherent capability and actually realizing it through integrating a nonnuclear bomber into nuclear training and operational plans.
5 Robert Farley, “The B-58 Hustler: America’s Cold War Nuclear Bomber Blunder,” The National Interest, June 10, 2016, https://nationalinterest.org/feature/the-b-58-hustler-americas-cold-war-nuclear-bomber-blunder-16547.
6 Ankit Panda, “Introducing the DF-17: China’s Newly Tested Ballistic Missile Armed With a Hypersonic Glide Vehicle,” Diplomat, December 28, 2017, https://thediplomat.com/2017/12/introducing-the-df-17-chinas-newly-tested-ballistic-missile-armed-with-a-hypersonic-glide-vehicle/; Hans M. Kristensen and Robert S. Norris, “Chinese Nuclear Forces, 2018,” Bulletin of the Atomic Scientists 74, no. 4 (2018): 289–295; Office of the Secretary of Defense, Military and Security Developments Involving the People’s Republic of China 2019; Hans M. Kristensen and Matt Korda, “Russian Nuclear Forces, 2019,” Bulletin of the Atomic Scientists 75, no. 2 (2019): 73–84; Defense Intelligence Ballistic Missile Analysis Committee, Ballistic and Cruise Missile Threat 2017, NASIC-1031-0985-17 (Wright-Patterson Air Force Base, Ohio: National Air and Space Intelligence Center, June 2017), 37; Sutyagin, Atomic Accounting, 85; and Hans M. Kristensen and Robert S. Norris, “United States Nuclear Forces, 2018,” Bulletin of the Atomic Scientists 74, no. 2 (2018): 120–131.
7 It does appear, however, that certain variants were used exclusively for nuclear operations during certain time periods. Pavel Podvig assesses that Russian bombers capable of carrying nuclear gravity bombs have always been dual-use. However, because all early Russian air-launched cruise missiles were nuclear-armed (with the possible exception of a conventional antiradar variant of the Kh-22 missile), he believes that Russia’s cruise missile-carrying bombers were originally involved exclusively in nuclear operations. Of Russia’s current bomber force, the Tu-160 and Tu-95MS bombers were probably the last to acquire a nonnuclear role. Pavel Podvig, e-mail communication, April 2016. See also Pavel Podvig, ed., Russian Strategic Nuclear Forces (Cambridge, MA: MIT Press, 2004), ch. 6.
8 Vladimir Putin, “Presidential Address to the Federal Assembly,” Moscow, March 1, 2018, http://en.kremlin.ru/events/president/news/56957.
9 Hans M. Kristensen, Robert S. Norris, and Matthew G. McKinzie, Chinese Nuclear Forces and U.S. Nuclear War Planning (Washington, DC: Federation of American Scientists & Natural Resources Defense Council, November 2006), 93–95 https://fas.org/nuke/guide/china/Book2006.pdf.
10 Office of the Secretary of Defense, Military and Security Developments Involving the People’s Republic of China 2019, annual report to Congress (Washington, DC: U.S. Department of Defense, 2019), 41, https://media.defense.gov/2019/May/02/2002127082/-1/-1/1/2019_CHINA_MILITARY_POWER_REPORT.pdf.
11 Director of Central Intelligence, Soviet Technical Capabilities in Guided Missiles and Space Vehicles, National Intelligence Estimate 11-5-61, April 25, 1961, Table IV, https://www.cia.gov/library/readingroom/docs/DOC_0000278407.pdf.
12 Author calculation.
13 The 1961 National Intelligence Estimate did not rule out the possibility of longer-range Soviet missiles being used for chemical weapons delivery “for certain limited purposes.” National Intelligence Estimate 11-5-61, 20.
14 Soviet Military Power 1985 (Washington, DC: U.S. Government Printing Office, April 1985), 38, states that deployments of the SS-12 Mod 2 to Eastern Europe began in 1984 but may imply that deployments within the Soviet Union began earlier. Separately, there is some uncertainty about whether the original SS-12 was dual-use. Soviet Military Power (Washington, DC: U.S. Government Printing Office, ), 31, states unambiguously that it was. Later editions are more equivocal. See, for example, [Soviet Military Power 1985], 38. Moreover, unredacted portions of a 1965 Central Intelligence Agency (CIA) memo about the SS-12’s deployment do not mention the possibility of its being conventionally armed. CIA, Office of Current Intelligence, “The SS-12,” Intelligence Memorandum, December 30, 1965, 1, RDP79T00472A000600060002, CREST System, https://www.cia.gov/library/readingroom/docs/CIA-RDP79T00472A000600060002-8.pdf.
15 U.S. Senate Armed Services Committee, Fiscal Year 1978 Authorization for Military Procurement, Research and Development, and Active Duty, Selected Reserve, and Civilian Personnel Strengths, Part 8, Research and Development, 95th Cong., 1st sess., March 2, 1977, 5313 and 5362, https://books.google.com/books?id=-c8QAAAAIAAJ.
16 Separately, in 1993, the CIA assessed that China had developed a nuclear warhead for the DF-15 missile, but it is likely that this missile has been deployed only in its conventional configuration. Kristensen and Norris, “Chinese Nuclear Forces, 2018,” 292; and Jeffrey Lewis, Paper Tigers: China’s Nuclear Posture, Adelphi 446 (Abingdon, U.K.: Routledge for the International Institute for Strategic Studies, 2014), 100.
17 Andrew S. Erickson, “Academy of Military Science Researchers: ‘Why We Had to Develop the Dongfeng-26 Ballistic Missile’—Bilingual Text, Analysis, and Related Links,” andrewerickson.com (blog), December 5, 2015, http://www.andrewerickson.com/2015/12/academy-of-military-science-researchers-why-we-had-to-develop-the-dongfeng-26-ballistic-missile-bilingual-text-analysis-links/; and Office of the Secretary of Defense, Military and Security Developments Involving the People’s Republic of China 2019, 44. Two variants of this missile, with slightly different canisters, have been observed. Both variants appear to be dual-use. Personal communication, Scott LaFoy, April 2019.
18 Panda, “Introducing the DF-17.”
19 Office of the Secretary of Defense, Military and Security Developments Involving the People’s Republic of China 2019, 44, 62, and 66. See also Lewis, Paper Tigers, 107–108 and 111.
20 Personal communication, Scott LaFoy, April 2019.
21 Personal communication, Scott LaFoy, April 2019. The CSS-5 Mod 6 is first mentioned in the 2016 edition of Military and Security Developments Involving the People’s Republic of China. See Office of the Secretary of Defense, Military and Security Developments Involving the People’s Republic of China 2016, annual report to Congress (Washington, DC: U.S. Department of Defense, 2016), 58.
22 Daniel Coats, statement on “Russia’s Intermediate-Range Nuclear Forces (INF) Treaty Violation,” November 30, 2018, https://www.dni.gov/index.php/newsroom/speeches-interviews/item/1923-director-of-national-intelligence-daniel-coats-on-russia-s-inf-treaty-violation. The U.S. intelligence community reportedly estimates its range to be 2,000 km with a conventional warhead or 2,350 km with a nuclear warhead. Ankit Panda, “U.S. Intelligence: Russia Tried to Con the World With Bogus Missile,” Daily Beast, February 18, 2019, https://www.thedailybeast.com/us-intelligence-russia-tried-to-con-the-world-with-bogus-missile.
23 Kremlin, transcript of “Meeting With Sergei Lavrov and Sergei Shoigu,” Moscow, February 2, 2019, http://en.kremlin.ru/events/president/news/59763. If the hypersonic missile is based on boost-glide technology, it would probably not have been prohibited by the INF Treaty, even if its range is between 500 km and 5,500 km. Payne et al, Conventional Prompt Global Strike, 30–32.
24 Matthew Bodner, “Russia Bids Farewell to INF Treaty With Fresh Nuclear Development Plans,” Defense News, February 6, 2019, https://www.defensenews.com/smr/nuclear-arsenal/2019/02/06/russia-bids-farewell-to-inf-treaty-with-fresh-nuclear-development-plans/.
25 If the weapons were based in silos or on naval platforms, then any ambiguity would technically be associated with the silo or vessel rather than the missile.
26 There have been a few reports that Avangard, a Russian intercontinental boost-glide missile, is dual-use. However, these reports are likely incorrect given the technical challenges of ensuring accuracy over such long distances and Putin’s failure to describe Avangard as dual-use, when he unveiled it on March 1, 2018, in contrast to his description of Kinzhal. Putin, “Presidential Address to the Federal Assembly.”
27 For an overview of this and similar programs, see Acton, Silver Bullet?, 10–11 and 37–44.
28 Office of the Secretary of Defense, Military and Security Developments Involving the People’s Republic of China 2019, 61 and 67.