In the past 18 months, North Korea sank a South Korean warship, the Cheonan, and bombarded Yeonpyeong Island in South Korea. Together, these two attacks killed 50 South Koreans. Moreover, it seems like further provocations might be on the way. These brazen acts threaten the credibility of US security commitments in Northeast Asia and have led to calls in South Korea for the United States to base nuclear weapons there and in Japan for building an independent nuclear deterrent. One Japanese academic has even posed the question, ‘Did deterrence against North Korea fail in 2010?’
Japanese and South Korean strategists have long worried that North Korea views its small nuclear deterrent as a shield. They argue that from behind this shield, and with the protection afforded by his hardened and deeply buried bunkers, a risk-taking Kim Jong-il believes he can launch limited offensive military operations against his neighbours with impunity. Strategic stability, our Asian allies argued during the 2010 Nuclear Posture Review, isn’t the same thing as regional security. On the contrary, a stable ‘balance of terror’ may embolden Pyongyang to continue attacks like the ones against the Cheonan and Yeonpyeong.
In response to North Korea's provocations, the United States and South Korea have agreed upon a series of measures to provide effective conventional military responses to North Korean provocations. Although such conventional retaliatory options are necessary, they aren’t sufficient. The United States must also find ways to make Kim significantly less confident in the protection he is provided by his elaborate tunnelling campaign. In particular, the United States must find a way to make him worry about the thing he most values: himself.
Getting at Kim means putting at risk North Korea’s growing number of hard and deeply buried targets. North Korea has sought to preserve its leadership and other valued assets, such as its nuclear and missile forces, by constructing underground facilities ranging from relatively shallow ‘cut and cover’ facilities to complexes buried beneath hundreds of meters of hard rock. Although most of these facilities can be threatened with conventional earth penetrators, a few may be too deep for conventional options, especially those where Kim himself might plan to hide. For the near future, only nuclear weapons could hold such targets at risk.
Yet the current earth penetrating warhead in the United States nuclear arsenal, the B61-11, is ill-suited for certain North Korean targets. The United States has long had an official requirement for a hard rock penetrator, but this requirement has been unmet since the Clinton administration – rightly in our view – decided to retire the aging B53 penetrator warhead because of safety and reliability concerns. The Clinton administration developed the B61-11 to replace the B53, but this newer warhead was designed to penetrate frozen tundra, like that found in Russia, and not hard rock like that found in North Korea.
Today, however, we don’t have to choose between safety and meeting reasonable, existing military requirements to hold at risk targets in hard rock. This is because the United States could meet the military requirements previously met by the B53 by modifying an existing warhead, the B83. (The National Nuclear Security Administration had planned to begin looking at B83 lifetime extension options soon, but it now appears this has been unnecessarily deferred to the mid-2020s.) Specifically, this military requirement could be met by simply changing the external casing of the warhead, providing better attitude control, and confirming that the configuration of internal components would survive the rapid deceleration accompanying penetration into a few meters of hard rock. As a first step, we would recommend that Sandia National Laboratories conduct a ‘sled test’ of a B83 (using a test assembly with no nuclear material) to assess the ruggedness of the non-nuclear components in a penetrator mode.
We should be clear that this would not require development of a ‘new’ nuclear weapon because it would be based on an existing weapon and a long-standing military requirement. Such an approach would be consistent with the policy of the Obama administration that stockpile modernization will ‘use only nuclear components based on previously tested designs, and will not support new military missions or provide for new military capabilities.’
Even so, our recommended effort might still evoke comparisons with the Bush administration’s controversial ‘Robust Nuclear Earth Penetrator’ study. To allay these concerns, however, the United States should make clear that, should an underground nuclear explosive test be necessary to confirm the reliability of a modified B83, it would look for other options to meet this military requirement.
Our proposal wouldn’t threaten strategic stability with Moscow or Beijing because of both the number and the nature of the weapons. First, the number of converted penetrators would be kept small, consistent with a niche capability against North Korea, which means they couldn’t threaten the redundant and variegated forces of Russia or China. In any event, we doubt Russia or China would be genuinely threatened by such an effort. Russian officials didn’t object to the development of the B61-11, even though that penetrator was clearly intended to defeat Russian targets in frozen tundra. Indeed, it’s also likely that many important Russian facilities are much too hard for even nuclear weapons.
Nor would our proposal make the B83 ‘more usable’ or lower the threshold for nuclear use. Such a penetrator could only be used, as the 2010 Nuclear Posture Review states, in extreme circumstances. Consistent with that reality, the United States should make clear that it would also invest heavily in conventional penetrators and functional defeat approaches that would provide the president with credible, indeed more desirable, non-nuclear options for holding at risk targets in hard rock. Kim will only be more cautious if he knows that the president has a full suite of options, including non-nuclear ones, to get at him wherever he may hide. Until then, however, his realization that he isn’t immune may help him reconsider some of his more reckless behaviour.
Our first priority at this moment is to ensure the security of allies, particularly Japan and South Korea. It is our security umbrella that allows each state to remain non-nuclear even in the face of North Korea’s provocative behaviour, including its testing and development of nuclear weapons. Since the end of the Cold War, however, the United States has deemphasized its tactical nuclear weapons, affirming that ‘it has no nuclear weapons on the Korean Peninsula’ in the 2005 Six Party Agreement and announcing plans to retire the nuclear-armed Tomahawk missile by 2013. In response to North Korea's provocative behaviour, calls have arisen in Japan for an independent nuclear capability and in South Korea for the emplacement of US tactical nuclear weapons. Neither of these would be positive developments, but they reflect genuine and reasonable security concerns. Compared to these outcomes, a new casing for the B83 seems a reasonable response to North Korea’s dangerous behaviour.
Kim Jong-il’s aggressive behaviour demonstrates the continuing importance of deterrence. The best US response is to maintain capabilities that clearly demonstrate to him that the United States has a credible and effective option to hold at risk what he values most, while preserving stability and respecting our international non-proliferation commitments. Such a capability would help encourage Kim to err on the side of caution when contemplating provocations that might escalate, such as the attacks on the Cheonan and Yeonpyeong. A modified B83 is just such a capability.
Jeffrey Lewis is Director of the East Asia Nonproliferation Programme at the James Martin Center for Nonproliferation Studies at the Monterey Institute of International Studies. He also founded and maintains the leading blog on nuclear arms control and nonproliferation, ArmsControlWonk.com. Before joining CNS, he was Executive Director of the Nuclear Strategy Initiative at the New American Foundation. Elbridge Colby is a research analyst at the Center for Naval Analyses, where he focuses on strategic, deterrence, proliferation, and related issues. From 2009 to 2010, he served as policy advisor to the Secretary of Defence’s Representative for the follow-on to the Strategic Arms Reduction Treaty.