North Korea is marching toward full-fledged nuclear-armed status, having conducted its first test of intercontinental ballistic missile (ICBM) in early July, quickly followed by another one. With this comes the risk that Pyongyang becomes more militarily aggressive, notably toward its neighbors: U.S. allies South Korea and Japan. In response, Washington, Seoul, and Tokyo should strengthen their deterrence and defense capabilities, postures, and policies. That requires heavy-lifting at the conventional level, but also adapting the nuclear posture, or “nuclear tailoring.”

Much has already been accomplished, especially since the sinking of the Cheonan and shelling of Yeonpyeong Island by Pyongyang in 2010. In consultation with its allies, Washington revised its nuclear policies and capabilities in the 2010 U.S. Nuclear Posture Review. Washington rejected the notion that the “sole purpose” of nuclear weapons is to deter nuclear attacks against the United States or its allies, and committed to modernizing the nuclear arsenal. The review also confirmed reliance on U.S. strategic forces for Northeast Asia and, while retiring the nuclear variant of its Tomahawk cruise missile, decided to maintain a capability to forward-deploy nuclear-capable bombers to visibly show American resolve during a crisis.

In addition, because U.S. allies increasingly face threats below the nuclear threshold, including in the “gray zone,” Washington has emphasized the role of non-nuclear capabilities, notably to improve defense (ballistic missile defense) or allow more flexibility to respond (conventional strike). In this spirit, the United States and Japan have developed, deployed, and operated missile defenses, both separately and together. In recent years, a debate has slowly emerged in Tokyo about Japan’s possible development of a modest strike capability. Moreover, while South Korea lagged behind Japan in acquiring advanced missile defense capabilities, it recently deployed U.S. Terminal High Altitude Area Defense (THAAD) batteries on its territory. The United States also supported an increase in the range of South Korean ballistic missiles, and there are reports that South Korean officials are seeking another increase.

Lastly, in 2010 Washington established bilateral deterrence dialogues with South Korea and Japan. Unlike in Europe, where the United States and its allies talk about these issues under the auspices of NATO, there was no such process in Northeast Asia, typically leaving allies on the receiving end of Washington’s decisions. Building on years of unofficial discussions, the U.S.-South Korea Deterrence Strategy Committee (and its companion, the Extended Deterrence Strategy and Consultation Group) and the U.S.-Japan Extended Deterrence Dialogue have filled this gap, giving Tokyo and Seoul a greater say in matters involving their security. Washington has also encouraged greater trilateral cooperation with Seoul and Tokyo, given that any crisis with North Korea would involve them both and the United States.

These efforts have helped enhance deterrence of Pyongyang and assurance of Seoul and Tokyo. Yet because North Korea’s arsenal is becoming increasingly sophisticated, work is needed to further adapt and strengthen capabilities, postures, and policies. Progress is essential at the conventional level, where the risks of conflict are more likely. Allies should double down on investing in missile defenses and strike capabilities, as well as other systems — notably intelligence, surveillance, and reconnaissance technology. They should also better integrate these systems at the trilateral level and ramp up efforts to coordinate response options in a crisis, which have remained limited so far because of political differences between South Korea and Japan.

Development of a missile strike capability is particularly attractive to help deny North Korea’s ability to initiate a preemptive attack. It is also an area ripe for allied cooperation: Washington cannot deploy intermediate-range missiles because of its obligations under the Intermediate-Range Nuclear Forces Treaty, but South Korea and Japan are not bound by this treaty and could therefore deploy such weapons, filling a gap in the regional deterrence architecture.

But that’s not all. Additional nuclear tailoring is also necessary, for two reasons. First, because Pyongyang may believe — mistakenly — that its improved nuclear arsenal enables it to also challenge Seoul, Tokyo, or even Washington at higher ends of the conflict spectrum. In private discussions I participated in several months before their ICBM tests, North Korean officials suggested that if they once saw their country as an India or a Pakistan, they increasingly seemed to consider it as the former Soviet Union: They believed then that they had already reached a situation of mutually assured destruction with the United States. Correcting these assumptions is paramount and requires, in part, adapting and strengthening the regional nuclear deterrence architecture.

Second, additional nuclear tailoring is critical because, for better or for worse, Seoul and Tokyo continue to attach great importance to the nuclear component of U.S. security guarantees. When asked how the United States can keep them assured, for instance, South Koreans and Japanese typically say Washington should refrain from over-emphasizing the role of conventional means over nuclear options. Failure to address these concerns could fuel incentives for independent South Korean and Japanese nuclear arsenals, which have seen small yet growing support, mostly in Seoul.

What, then, should additional nuclear-tailoring look like in Northeast Asia? Some in the United States argue for a closer, NATO-like relationship between Washington, Seoul, and Tokyo. They explain that Washington should continue to rely on strategic forces and nuclear-capable bombers, but that it may also want to deploy dual-capable aircraft, which could be hosted in South Korean and/or Japanese airbases, along with U.S. tactical nuclear weapons. In part because U.S. options to deploy such weapons are limited due to the retirement of many of the weapons previously stationed in the region (during the Cold War), the same people also often call for the development of a low-yield weapon. They add that such a discriminate capability would strengthen deterrence because it would signal to Pyongyang greater U.S. readiness to retaliate, which Washington may not have or be able to signal with just high-yield weapons in its inventory. As in NATO, the local presence of U.S. nuclear assets would help, the argument goes, visibly signal the collective nuclear resolve of the United States and its Northeast Asian allies vis-à-vis Pyongyang.

South Korea and Japan have been consistent in requesting a more NATO-like relationship with the United States and, therefore, the option to deploy permanent U.S. nuclear assets to the region has gained ground in recent years, particularly in South Korea. Although it may lose momentum under the presidency of Moon Jae-in (who is more moderate than his predecessor), a small yet growing constituency of South Koreans has been calling for such deployment. As a group of conservative South Korean activists put it after North Korea’s fifth nuclear test in September 2016, “The South Korean government must cooperate fully with the United States in order to deploy tactical nuclear weapons on the Korean Peninsula.” The idea is also gaining traction in Japan, even though Japanese do not argue for deployment on their territory. A recent Japanese report explains:

If North Korea […] intends to continue nuclear tests and missile launches, it is desirable to redeploy tactical nuclear weapons at the US military bases in South Korea as a counter measure [emphasis added].

Of note, however, is that many South Korean and Japanese advocates for such deployment regard it less as a deterrence or warfighting option than as a last-resort attempt to pressure China to push North Korea, its patron, toward denuclearization. In other words, deployment would essentially act as a bargaining chip.

The problem is that deploying U.S. nuclear assets in Northeast Asia would be both unnecessary and counterproductive. It would be unnecessary because, in its general form, the current arrangement of extended nuclear deterrence based on U.S. strategic forces and deployable nuclear-capable bombers is efficient and well-suited to the regional security environment. The U.S. triad is capable of any necessary nuclear employment and, in a crisis, alert levels can be changed and bombers can be used visibly, as was the case in March 2013 (and subsequently), when they were flown into South Korean airspace in response to North Korean provocations. The presence of U.S. nuclear assets in theater would do little to improve deterrence of North Korea. Neither would — or should — this enhance assurance of South Korea or Japan. On the contrary, such a deployment would likely urge Pyongyang to target these assets, making Seoul and Tokyo less safe.

Meanwhile, the idea that deploying U.S. nuclear assets to the region can be used as a bargaining chip to pressure Pyongyang (via Beijing) into denuclearizing rests on flawed logic. Should deployment take place, Beijing is less likely to squeeze Pyongyang than to ramp up its own military modernization program, for one simple reason: Chinese officials would see such a move as an American excuse to target them and achieve “strategic primacy.” While acknowledging that the THAAD deployment on the Korean Peninsula provides limited defense benefits to South Korea against North Korean missiles, Beijing believes ― wrongly ― that this system is primarily intended to weaken China’s strategic deterrent while contributing to an expanding global anti-missile architecture that threatens both Beijing and Moscow.

Beijing would draw similar conclusions if U.S. nuclear assets were deployed in Northeast Asia, especially given that, unlike missile defenses, these systems are not defensive weapons. It would feel vindicated that Washington’s true goal is to target China and would respond with a strong military build-up, raising tensions in the U.S.-Chinese strategic relationship at a time when they are already — and have been for several years — on an upswing, notably over the South China Sea.

There’s good news, however: Washington can do additional nuclear tailoring in Northeast Asia without deploying further assets. It can do so within the confines of the current regional security arrangement, which works, and in a manner which would help increase deterrence of Pyongyang and assurance of Seoul and Tokyo, while avoiding feeding (too much) into Beijing’s worst fears. That can be achieved by sharing more information with Seoul and Tokyo about how the United States thinks about nuclear weapons and their roles in both peacetime as well as during crises and wars. Additionally, Washington should give both allies a role in support of US nuclear operations by establishing a mechanism similar to NATO’s SNOWCAT program, (short for “Support of Nuclear Operations With Conventional Air Tactics”).

Nuclear Information-Sharing

The establishment of deterrence dialogues with South Korea and Japan in 2010 was motivated by a recognition that, as Tim Sullivan has put it, South Korean and Japanese officials “want more than verbal reassurances [about American security guarantees]; they want to know how deterrence works.” Years later, the dialogues have borne fruit: They have built understanding in Seoul and Tokyo of how deterrence works, helping them feel assured. They have done so by institutionalizing policy discussions and development on these issues, and, more importantly and as detailed earlier, by ensuring continuous progress on practical agendas of cooperation to adapt and strengthen the Northeast Asian security architecture. In sum, these dialogues have increased understanding of deterrence by Seoul and Tokyo by making it a joint enterprise, at least on a bilateral basis between the United States and its two allies.

This collaborative work, however, has been conducted at the low and medium ends of the conflict spectrum. In the event of escalation to higher ends, including at the nuclear level, the U.S. message to South Korean and Japanese officials has been that the U.S. strategic deterrent would apply. Yet seldom have U.S. officials unpacked and explained the thinking process that goes into American nuclear deterrence and employment strategies. Accordingly, the role of U.S. nuclear weapons has remained obscure to South Korean and Japanese officials.

Washington should share more information with Seoul and Tokyo about how it thinks about nuclear deterrence and nuclear employment, how these strategies work or would work in a given situation, and how and how much in advance Seoul and Tokyo would be notified if a decision to use nuclear weapons were made. As a starting point for this discussion, the three allies might want to work together or in the bilateral tracks on the “sole purpose formulation,” which the U.S. Nuclear Posture Review rejected but left open its possible adoption in the future if proper conditions can be created. They might want to reflect on what these conditions could be and whether or how it would be possible to create them in Northeast Asia.

A Northeast Asian SNOWCAT

Washington should also give Seoul and Tokyo a role in support of U.S. nuclear operations. Recently, the U.S. Air Force has already begun coordinating many of its activities with its South Korean and Japanese counterparts, including its nuclear missions. Used as a “flexible deterrent option,” defined by the U.S. military as “pre-planned, deterrence-oriented actions tailored to signal and influence an adversary’s actions,” U.S. strategic bombers have touched down in South Korea. They have also been escorted by fighters from the South Korean and Japanese air forces.

After North Korea’s second ICBM test, for instance, two U.S. B-1 bombers originating from Guam flew to Japanese airspace, where they were joined two F-2 fighter jets from the Japanese Air Force. The B-1s then flew over the Korean Peninsula where they were joined by four F-15 fighter jets from the South Korean Air Force. Then, the B-1s performed a low-pass over Osan Air Base in South Korea, before leaving the South Korean airspace and returning to Guam. Described by U.S. military officials as a defensive show of force and unity from the three allies, the mission enabled the three aircrews to practice intercept and formation training, thereby improving their combined capabilities and tactical skills, while strengthening their long-standing military-to-military relationships.

Institutionalizing these activities by establishing a SNOWCAT mechanism is the logical next step and would help systematize and therefore better coordinate and strengthen allied actions. In NATO, the SNOWCAT program concerns participation by non-nuclear allies in a common nuclear mission by suppression of enemy air defenses, aircraft refueling, or search and rescue operations. Moreover, these missions are regularly exercised and symbolize the willingness of non-nuclear allies to contribute to NATO nuclear operations even if they do not have DCA or TNW on their territory. A SNOWCAT program, accordingly, would apply well to Northeast Asia.

Ramping up information-sharing on American nuclear deterrence and employment strategies and creating a SNOWCAT program with Seoul and Tokyo would offer significant benefits without the drawbacks that come with deploying new U.S. nuclear assets to the region. Enhancing “nuclear closeness” between Washington, Seoul, and Tokyo in such a way would help improve deterrence of Pyongyang: It would further demonstrate to North Korea that the three allies stand united in the event of escalation. By giving them more information and a more institutionalized role in U.S. nuclear operations, this approach would also help augment assurance of Seoul and Tokyo without inflaming the anti-nuclear communities in each country. Finally, while Beijing would be critical, it can be made to understand that these steps are necessary given Pyongyang’s actions; Beijing should also receive assurances that these steps would be scaled down if China moved aggressively to punish North Korea.

This proposal will be criticized both by the deterrence and disarmament communities. While the former will say that it does not go far enough, the latter will argue that it goes too far, notably in the direction of establishing nuclear sharing arrangements a la NATO in Northeast Asia. Yet the rising challenges posed by North Korea’s nuclear arsenal demand action, including in the nuclear realm. The agenda outlined here provides the most efficient response.

David Santoro (david@pacforum.org) is director and senior fellow for nuclear policy at the Pacific Forum, Center for Strategic and International Studies (CSIS). You can follow him on Twitter at @DavidSantoro1.

Image: U.S. Air Force photo by Staff Sgt. Nick Wilson