Japan’s New National Security Strategy

Getting Committed to the Defense of Taiwan

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This report is part of Strategic Japan, a CSIS Japan Chair initiative featuring analysis by Japan’s leading foreign policy scholars on key regional and global challenges and the implications for the U.S.-Japan alliance.


With the introduction of three security policy documents—the National Security Strategy, National Defense Strategy, and Defense Buildup Program—approved by the cabinet on December 16, 2022, Japan has clarified its intention to make a full-fledged contribution to the defense of Taiwan and to build the capabilities necessary to achieve that goal. If war breaks out across the Taiwan Strait, Japan will provide bases to the U.S. forces fighting for Taiwan and commit the Self-Defense Forces (SDF) to defend Taiwan in conjunction with the United States. The Japanese government has already affirmed the importance of peace and stability across the Taiwan Strait through statements at the U.S.-Japan summit meetings and other venues and has recognized that it is an “indispensable element for the security and prosperity of the international community.” 

Security on the Korean Peninsula continues to be important. Japan has been committed to the defense of South Korea since 1999, when it enacted a law to enable the SDF to assist U.S. forces in Korean contingencies. The United States and Japan have already formulated a combined operation plan for the defense of South Korea, and the new National Security Strategy states that South Korea is in an important geopolitical position with implications for Japan’s security. In other words, Japan is now committed to the defense of both Taiwan and South Korea.

Now that the policy goals and directions are set, Japan will likely face some critical issues and challenges going forward. This paper discusses four issues: (1) the security challenges that Japan faces from North Korea and China; (2) the seven critical areas of Japan’s defense improvement plan; (3) the challenges that Japan will face in implementing that plan; and (4) the crucial factors that could seriously constrain Japan’s role in maintaining security across the Taiwan Strait and on the Korean Peninsula.

Japan’s Security Challenges


Nuclear North Korea

The Stockholm International Peace Research Institute (SIPRI) estimates that North Korea possessed approximately 20 nuclear weapons and sufficient fissile material for 45 to 55 nuclear devices as of January 2022. In the 12 years following its first detonation test in 2006, North Korea has conducted six nuclear tests, with explosion yield increasing steadily from less than 1 kiloton in the first test to 160 kilotons in the sixth test. Through efforts targeting the miniaturization of nuclear weapons, North Korea has probably also acquired the capability to mount nuclear warheads on ballistic missiles. Furthermore, given the dramatic increase in explosion yield over previous tests, the sixth North Korean nuclear test appears to have involved a hydrogen bomb. North Korea characterized its sixth test as “a test of H-bomb for ICBM [intercontinental ballistic missile]” and “a very significant occasion in attaining the final goal of completing the state nuclear force.”

North Korea possesses some 700 to 1,000 ballistic missiles, of which 45 percent are short-range missiles, another 45 percent are medium-range missiles, and 10 percent are intermediate- to long-range missiles. Many of those missiles are mounted on transporter erector launchers. North Korea continues to develop and test new types of missiles and has steadily improved its missile technology and operational capabilities.

Given the country’s recent improvements in missile capabilities, Pyongyang seems to be seeking to enhance the survivability, readiness and responsiveness, and range of its missiles, as well as the ability to penetrate adversaries’ missile defense shields. Higher survivability has resulted from the introduction of land-, train-, and sea-based mobile launcher platforms. Some of the land-based launchers are wheeled, with a focus on speed, while others are tracked, focused on all-road ability. Solid-fuel missiles will reduce the time required for fueling and, therefore, pre-launch vulnerability. The deployment of solid-fuel missiles is also instrumental in improving the readiness and responsiveness of North Korean missiles. North Korea has been gradually developing short- to long-range missiles capable of striking targets near and far, including South Korea, Japan, Guam, Hawaii, and the U.S. mainland. North Korea has fired multiple missiles simultaneously for saturation attacks and has launched missiles with lofted trajectories and with maneuverable warheads to improve its capability to penetrate adversaries’ missile defense shields. It is also developing other missiles that can fly at low altitudes on irregular trajectories.

Rising China

In East Asia, the balance of power has been shifting rapidly in favor of China. According to SIPRI, while U.S. defense expenditures increased by 2.7 percent between 2013 and 2022, China’s defense spending soared by 63 percent in the same period. In absolute terms, the United States remained in first place globally, spending $877 billion in 2022, while China was in second place at $292 billion. However, it must be noted that while the U.S. military is globally committed, the Chinese military is only regionally engaged. When one considers the long-term trends and Japan’s defense spending of $46 billion in 2022, it is clear that it will be difficult for the United States and Japan to keep competing with China without significant policy changes on the U.S.-Japan side.

Of particular concern is the strengthening of China’s missile capability. According to the U.S. Department of Defense’s annual report, Military and Security Developments involving the People’s Republic of China 2022, China has deployed more than 600 short-range ballistic missiles with a range of 300 to 1,000 km, over 500 medium-range ballistic missiles with a range of 1,000 to 3,000 km, and more than 250 intermediate-range ballistic missiles with a range of 3,000 to 5,500 km. It also possesses 300 intercontinental ballistic missiles with a range of 5,500 km or more, as well as over 300 ground-launched cruise missiles with a range of 1,500 km or more.

Seven Critical Areas

Against the backdrop of the rapidly growing military capabilities of North Korea and China, Japan has announced a force improvement plan that emphasizes seven areas: (1) standoff strike capabilities, (2) integrated air and missile defense capabilities, (3) unmanned assets, (4) cross-domain operations, (5) command, control, and intelligence, (6) force mobility and civil defense, and (7) sustainability and resilience. The overall goal of Japan’s force improvement plan is to enhance its warfighting capabilities. In other words, while the previous defense force development plans focused on the acquisition of major equipment such as combat vehicles, naval vessels, and fighter aircraft, the current plan emphasizes how to maximize the utility of the major weapon systems in war. This section briefly discusses the important points of each item here.

  1. Standoff Strike Capabilities: The plan calls for the introduction of air-, land-, and sea-based long-range anti-ship and land-attack missiles to strengthen the defense of the Senkaku Islands and other islands and, if necessary, to enable strike operations against targets in enemy territories.
  2. Integrated Air and Missile Defense Capabilities: As in the past, Japan will continue to operate assets such as the SM-3 sea-based, upper-tier exoatmospheric missile defense system and the Patriot PAC-3 land-based, lower-tier endoatmospheric missile defense system, while also strengthening its ability to respond to air threats, including cruise missiles and hypersonic weapons.

    Interestingly, the Japanese government defines strike operations against adversaries’ territories as part of its efforts to enhance “integrated air and missile defense” capabilities, to maintain the internal logic that Japan still upholds its “exclusively defensive defense” (専守防衛) policy. In addition, since the Japanese government takes the position that preemptive strikes are illegal, it uses the term “counterstrike capability” instead of “strike capability” to emphasize the point that it would commence strike operations only after its adversaries initiated attacks against Japan. (In contrast, the U.S. and South Korean governments regard preemptive strikes as within the scope of the right of self-defense and as legal.)

    Contrary to the expectation of some experts that Japan will undertake preemptive strikes against North Korea or China, Japan is unlikely to do so for three First, Japan is simply too far away from North Korea and China. South Korea is developing a “kill chain” to preempt North Korea’s nuclear or missile strikes, and it makes sense for South Korea to do so because South Korea is in close proximity to North Korea and therefore in a good position to undertake preemptive strikes. The same does not apply to Japan. Second, Japan does not possess the necessary weapons systems to undertake preemptive strikes effectively. Japan is acquiring strike capabilities, but most of them are cruise missiles, much slower than the ballistic missiles that North Korea and China have in large numbers. That would be remedied somewhat if Japan acquired hypersonic weapons, but they will not be developed and deployed anytime soon. Unlike Japan, South Korea has been acquiring strike assets such as Hyunmoo 2 ballistic missiles and the short-range Army Tactical Missile Systems so that it can hit targets quickly. Finally, it is highly unlikely that Japan will launch preemptive strikes against North Korea or China even if it can. Since information is not perfect, launching preemptive strikes can ignite a war inadvertently. Japan fears getting dragged into a war on the Korean Peninsula or across the Taiwan Strait and is not interested in initiating a conflict in either theater.
  3. Unmanned Assets: Japan will strengthen its air, maritime, underwater, and land-based unmanned assets. The use of unmanned assets is expected to enhance operational effectiveness and compensate for the lack of human resources resulting from the country’s declining birthrate and aging population.
  4. Cross-Domain Operations: Operations in the space, cyber, and electromagnetic domains have become important policy agendas, to the extent that people in the Japanese security community now use the term “Usaden” (宇サ電), or “space, cyber, and electromagnetic.” In 2026, the SDF will begin operating space-based optical telescopes to enhance its space domain awareness. The Japan Air Self-Defense Force (JASDF) oversees the space domain operations and, to clarify that role, will be renamed to the Air and Space Self-Defense Force in time. In the cyber domain, the Japan Ground Self-Defense Force (JGSDF) will play a central role in expanding infrastructure and developing necessary human resources. In the electromagnetic domain, the JGSDF, JASDF, and Japan Maritime Self-Defense Force (JMSDF) will acquire and enhance electronic warfare equipment to strengthen their capabilities.
  5. Command, Control, and Intelligence: Strengthening intelligence-gathering capabilities, speeding up decisionmaking, and developing a network for command and control are the keys here. In addition, with the introduction of long-range strike capabilities, targeting will become an important addition to intelligence, surveillance, and reconnaissance capabilities.
  6. Mobility and Civil Defense: The SDF will acquire medium and small vessels, transport ships, and transport aircraft to rapidly deploy forces and equipment to the Southwest Islands in the event of a Taiwan contingency. Civil defense is also emphasized. Evacuating residents on the western part of the Southwest Islands in a crisis or war is one of the most important agendas.
  7. Sustainability and Resilience: Securing ammunition, petroleum, oil, and lubricants and enhancing the resilience of Japan’s armed forces are critical. To enhance sustainability, the Ministry of Defense plans to construct many ammunition depots, expand its domestic ammunition production capacity, and promote joint use of U.S. military facilities. To strengthen resilience, it will reinforce military facilities, build underground facilities, make major command centers resilient to electromagnetic pulse attacks, and better protect fighter aircraft.

The Roles of Strike Capabilities

One of the most controversial elements of Japan’s new defense strategy is the acquisition of strike capabilities. One can think of upsides and downsides, but there are at least four expected benefits.

First, Japanese strike capabilities would help maintain missile force balance in the region. North Korea and China together possess more than 800 ballistic missiles capable of reaching Japan, and their missile forces are growing. Therefore, Japan’s decision to acquire strike capabilities is expected to alleviate the growing missile gap in the region.

Second, Japanese strike capabilities would supplement missile defense. In recent years, North Korea has been improving its ability to penetrate Japan’s missile defense networks by conducting “saturation attack” drills, in which three to four missiles are launched simultaneously, as well as by launching missiles in a lofted trajectory. If Japan acquired meaningful strike capabilities, North Korea would be forced to conduct offensive missile operations while taking evasive actions, making Japan’s missile defense operations easier.

Currently, the Ministry of Defense estimates that Japan’s missile defense interceptor inventory is only 60 percent sufficient. Although there is a plan to increase the figure to 100 percent by 2027, North Korea and China will likely also increase their missile inventories. Moreover, missile defense interceptors are usually two to three times as expensive as ballistic missiles. For that reason, too, it makes sense for Japan to use both offensive and defensive means of protection.

Third, Japanese strike capabilities would ease potential dilemmas in prioritizing targets. China has more than 550 ballistic missiles that can hit U.S. territories, and North Korea is developing missiles that can reach Guam, Hawaii, and the U.S. mainland. In wartime, U.S. decisionmakers will face targeting dilemmas: while destroying missiles targeted at Japan is necessary for fulfilling their treaty obligations and protecting their forces stationed in Japan, prioritizing the destruction of missiles targeted at the United States would also be a political imperative. Under such circumstances, if Japan can take on adversaries’ missiles targeted at its own territory, that would ease the targeting dilemma between the U.S. and Japanese allies.

Finally, Japan’s strike capabilities would also enhance cohesion among allies and friends in wartime. If Japan does not have strike capabilities and leaves missile-hunting operations to U.S. and South Korean forces, Japan would be criticized as a free rider. Missile-hunting operations are a dangerous business. Imposing that risk on Americans and South Koreans alone is not a politically viable option. If the South Koreans ask Japan not to conduct strike operations on the Korean Peninsula, Japan could stay out without being blamed for free riding.

Obstacles to Policy Implementation

Japan is on the way to strengthening its warfighting capabilities, especially in the seven areas discussed above. However, there are some obstacles to the implementation of Japan’s new policy measures.

First, a tax hike is planned to secure significantly increased defense spending, but opinions on this issue are divided even within the ruling Liberal Democratic Party, and its handling of the matter will be an important political issue in the future.

As of 2022, Japan’s government debt was estimated to be around $10 trillion, the highest in the world. Its general government gross debt-to-GDP ratio is also one of the highest in the world, at around 260 percent. Spending more on defense is important from a national security standpoint, but if it overburdens the nation’s economy, it could be counterproductive in the long run.

Second, it is also a challenge to enable the SDF to use nonmilitary and commercial facilities and assets. For example, to disperse highly capable but highly vulnerable fighter aircraft in crisis or war, the SDF should be able to use commercial airports. However, that will require coordination among relevant ministries and agencies, local governments, private entities, and local communities. The Ministry of Land, Infrastructure, Transport and Tourism must work hard to coordinate with many different players. Even if the right to use those facilities and assets is granted, necessary adjustments and construction must follow to make it possible for the SDF to use nonmilitary assets and facilities effectively.

Third, securing a sufficient level of ammunition reserves is critical, but the so-called NIMBY (“not in my backyard”) problem will arise when locating ammunition depots. Currently, there are some 1,400 ammunition depots in Japan, and the Ministry of Defense seeks to add about 130 facilities by 2035. Of those 130 facilities, the JGSDF will construct about 90 and the JMSDF will build about 40. Among the first projects, four large ammunition depots, which will accommodate anti-ship and ground-attack missiles, will be constructed in army barracks in Oita and a naval base in Aomori in FY 2023. Another 40 to 50 of those facilities will be built in the next five years. Since many of the ammunition depots are concentrated in northern Japan, future construction will mainly occur close to the Taiwan Strait.

The Ministry of Defense’s construction of new army barracks in Miyako and Ishigaki Islands in Okinawa took four years and seven years, respectively. In Miyako, the Ministry of Defense filed a request to the city in 2015, obtained approval in 2016, and activated the barracks in 2019. In Ishigaki, the Ministry of Defense filed a request to the city in 2015, obtained approval in 2018, and activated the barracks in 2023. Obtaining approval from local governments and building consensus in local communities will be critical factors in building the necessary facilities to enhance the effectiveness of the SDF’s operations.

Strategic Challenges

While there are practical challenges to the implementation of the policy measures discussed above, there are some fundamental, potentially more important strategic challenges.

Military Coercion

Maintaining Japan’s commitments to the defense of South Korea and Taiwan in the face of North Korean and Chinese military coercion would be a challenge in a crisis or war. If there is a war on the Korean Peninsula or across the Taiwan Strait, Japan would play two critical roles. First, Japan would provide bases in Misawa, Yokota, Atsugi, Yokosuka, Iwakuni, Sasebo, Kadena, Futenma, and elsewhere to U.S. forces fighting to help South Korea or Taiwan. Japan has invested over $20 billion to deploy ballistic missile defense systems to help protect the U.S. forces and bases in Japan. The SDF also has the important mission of guarding U.S. military facilities.

Second, in the event of war, the SDF would operate closely with U.S. forces in defense of South Korea or Taiwan. The Peace and Security Legislation enacted in 2015 made it possible for Japan to start exercising the right of collective self-defense and participate in combat operations in defense of its friends and allies, namely South Korea, Taiwan, and the United States. Operationally, the SDF can now intercept ballistic missiles headed for Guam and Hawaii, participate in anti-air and anti-submarine operations, and sweep or lay mines in the waters around North Korea and the First Island Chain.

One point of concern, however, is that maintaining the credibility of Japan’s commitments to the defense of South Korea and Taiwan is becoming more difficult by the day. In a crisis or war, North Korea and China would seek to coerce Japan (and the United States for that matter) into neutrality. They would say things such as: “Would you be willing to sacrifice Tokyo (or Washington) for Seoul or Taipei?” or “We have no intention of attacking you if you simply stay out and decide not to interfere with our internal affairs.” In an extreme scenario, North Korea and China might explode a nuclear bomb in the air near Japanese territory or even use nuclear weapons against Japanese naval vessels to coerce Japan into neutrality. While using nuclear weapons against the United States would not be an option, using them against Japanese targets without creating large collateral damage could be. U.S. forces would not be able to fight effectively on the Korean Peninsula or across the Taiwan Strait if Japan decided to prohibit the United States from using bases and to not commit the SDF to the defense of South Korea or Taiwan.

Not many Japanese citizens realize that Japan is militarily committed to the defense of South Korea and Taiwan. North Korea and China would use all available means to convince the Japanese people that they are getting entrapped in somebody else’s war. That would put Japanese people and political leaders in a very difficult position.

Two-Theater Commitment

Since the U.S.-Japan alliance is committed to the defense of South Korea and Taiwan simultaneously, the security environment on the Korean Peninsula will affect the security environment across the Taiwan Strait and vice versa. Both North Korea and China continue to strengthen their military capabilities, putting a larger defense burden on the U.S.-Japan alliance.

In that context, of particular concern is the possibility that North Korea’s improved nuclear and missile capabilities force the United States and Japan to divert more of their anti-submarine warfare and air and missile defense assets away from the Taiwan Strait. For example, the ballistic missile submarines that North Korea is developing emit considerable noise, so their effectiveness as a nuclear deterrent is questionable. However, they could still serve as a means of diverting critical U.S. and Japanese anti-submarine warfare assets away from the Taiwan Strait. Such submarines carry nuclear weapons; the United States and Japan could not afford to ignore them. It would be a critical drawback if, in a time of crisis or war, the United States and Japan were unable to commit most of their anti-submarine warfare capabilities to the defense of Taiwan.

North Korea’s development of long-range cruise missiles is another source of concern. In 2021, North Korea announced that it had conducted a test launch of a cruise missile with a range of more than 1,500 km. In the past, ballistic missiles were the only meaningful threat that North Korea posed to Japan. But the additional threat posed by cruise missiles would force Japan to divert its air defense assets away from the Taiwan Strait.

In case of war across the Taiwan Strait, China might decide to encourage North Korea to create tension on the Korean Peninsula to draw U.S. and Japanese forces away from Taiwan. With the security of the Korean Peninsula and the Taiwan Strait becoming more intertwined, China might increase its military support to North Korea for diversionary purposes.

Conversely, if the crisis on the Korean Peninsula heightens, China may perceive an opportunity to take Taiwan. If there is a conflict on the Korean Peninsula, the United States and Japan might decide to move their forces southward to prevent China from attacking Taiwan while the U.S.-South Korea alliance responds to North Korea’s aggression.

As the Biden administration’s 2022 Nuclear Posture Review suggested, if a conflict occurs on the Korean Peninsula or across the Taiwan Strait, China or North Korea might engage in “opportunistic aggression” in the other theater. The Biden administration recognizes the potential for near-simultaneous conflict with two nuclear-armed states and declared that the United States would “rely in part on nuclear weapons” to help mitigate such risk.

Finally, there is one possibility of intra-theater diversionary action by China. If China is to attack Taiwan, it might attempt to foment a crisis over the Senkaku Islands to keep Japanese forces away from Taiwan. In one scenario, Japan might even use the need to defend the Senkaku Islands as an excuse to stay away from Taiwan. Alternatively, the United States might use the need to defend Taiwan as an excuse to stay away from the Senkaku Islands. U.S. and Japanese planners must seriously think about how to deal with China’s possible attempt to turn those scenarios into reality.

Policy Recommendations


Enhance Awareness of Japan’s Security Roles

There is a widely held belief that the U.S.-Japan alliance is there to defend Japan. In reality, the U.S.-Japan alliance is there to mainly defend South Korea and Taiwan. The active U.S.-Japan combined operation plan—OPLAN 5055—is designed for dealing with a Korean contingency. Moreover, the United States and Japan are reportedly formulating a new operation plan for contingencies across the Taiwan Strait.

Former prime minister Abe Shinzo once said, “A Taiwan contingency is a contingency for Japan.” His statement is right in the sense that China would attack Japan if it decided to attack Taiwan. Unless China destroys a significant part of the U.S. and Japanese forces deployed in Japan in the early stages of the war, it would be difficult for it to take Taiwan. However, Abe’s statement downplays the fact that Japan has a choice: it can enter the war or stay out. After all, all NATO countries decided to stay out when Russia attacked Ukraine. The problem is that if China expects Japan to stay out, the likelihood of war breaking out across that Taiwan Strait will increase.

One of China’s most important objectives in a war across the Taiwan Strait would be to neutralize the United States and Japan and, if that fails, undermine their capability to assist Taiwan as much as possible. The same applies to the Korean Peninsula. North Korea’s sworn enemy is South Korea, not Japan. South Korea is the only country with the potential ability and willingness to absorb North Korea and unify the Korean Peninsula. Only South Korea can pose an existential threat to North Korea. In contingency situations, North Korea would use or threaten to use its nuclear weapons and missiles against the United States and Japan to keep them out of the war. Here again, North Korea would be attacking Japan not for the sake of attacking Japan but for the sake of neutralizing it or, short of that, undermining its ability to assist U.S. forces fighting to defend South Korea.

Enhancing the understanding of this reality is critical for at least two reasons. First, unless Japanese political leaders and citizens understand the commitment that they are making to the defense of Taiwan or South Korea, it would be difficult for them to resist psychological warfare or influence operations that China and North Korea would conduct. In a crisis or war, China and North Korea would likely declare that they do not want to fight with Japan and that they will not attack Japan if it remains neutral. (They would say the same thing to the United States.) Political leaders and people in Japan would be able to resist such an overture only if they had made a conscious decision and judgment that defending Taiwan or South Korea is necessary and in Japan’s vital national interest.

Second, enhancing the understanding of Japan’s commitment to the defense of Taiwan and South Korea on the part of policymakers and specialists in the United States would help maintain alliance cohesion and avoid unnecessary friction between the United States and Japan. Not all specialists in the United States understand that the United States and Japan are in the same strategic position to defend South Korea and Taiwan. The Japanese, like the Americans, are concerned about getting entrapped in a war on the Korean Peninsula or across the Taiwan Strait. The United States and Japan will be able to find the best way to remain united in a crisis or war if they understand how both countries face the same dilemma of maintaining security commitments and avoiding entrapment.

Step Up Civil Defense Exercises

Since the Civil Protection Law was enacted in 2004, Japan has introduced civil defense measures and conducted civil defense exercises. The text-based warning system, called Emergency Network (Em-Net), was introduced in 2006, and the siren- and voice message-based automated warning system, called J-Alert, was installed in 2007. The early warning systems are designed to reduce civilian casualties in contingencies. In the event of a war, in addition to military infrastructure, major cities could become targets. An early response would help reduce damage significantly.

Civil defense exercises based on a missile attack scenario began in 2017. By the end of FY 2021, 489 such exercises had been conducted in 45 prefectures, including 29 exercises jointly organized by the central government and prefectures and municipalities around the country. In FY 2022, two civil defense exercises based on the missile attack scenario were conducted in Okinawa for the first time—one on Japan’s westernmost island, Yonaguni Island, in November 2022 and another in the prefectural capital city of Naha in January 2023.

There are challenges. J-Alerts has failed to issue warnings on some occasions and has issued false alarms on others. When a missile from North Korea flew over northern Japan in 2022, an alarm went off in not only northern Japan but also some islands to the south of Tokyo. Moreover, the alarm went off only belatedly when the missile was already overhead. However, those events might prove useful in the long run if those problems are fixed quickly. Failures can be the mother of improvement.

A more fundamental issue is the fact that civil defense exercises have been conducted only in small to medium-sized cities, where missiles are unlikely to hit. Exercises in urban areas are needed. However, conducting civil defense exercises in urban areas is not easy because that would disrupt socioeconomic activities significantly and could result in accidents or even panic. The government must find a way to enhance civil defense preparedness in urban areas while minimizing disruptive effects.

Conducting civil defense exercises will also contribute to enhancing psychological defense, making the Japanese population less vulnerable to influence operations and military coercion. If a larger number of Japanese citizens understand the characteristics of the military threats that they face and how they might be able to protect themselves, their ability to stand up against enemy coercion will improve. The Japanese government must take that psychological defense aspect into account when it organizes civil defense exercises in the future. For example, it could be beneficial to organize lectures and discussion sessions during civil defense exercises on how civil defense measures have saved human lives in past wars or how extended deterrence is supposed to work.

Enhance Understanding of Deterrence

Russia’s suggestion that it may use tactical nuclear weapons in Ukraine has heightened anxiety among people in Japan. Although there were serious discussions among experts about the possibility of use or threat of use of nuclear weapons by Russia, China, and North Korea even before the war in Ukraine, the seriousness of the issue has grown with Russia’s invasion of Ukraine.

The war in Ukraine has produced negative and positive results. On the negative side, the perception that nuclear weapons can be used coercively and fairly successfully has become more widespread. Russia’s nuclear coercion seems to have made NATO countries highly cautious in assisting Ukraine. On the positive side, despite acknowledging its ability to do so, Russia has not used nuclear weapons yet, or not “escalated to de-escalate.” The nuclear threshold remains high. In addition, the logic of nuclear deterrence and extended nuclear deterrence has become more widely understood in Japan. Since the outbreak of the war in Ukraine, security specialists have been sharing their professional knowledge on security issues, including nuclear deterrence, with a large number of Japanese citizens sitting in front of their TVs or computers. By now, a larger number of Japanese people than ever before understand what extended nuclear deterrence is and how it might work. That knowledge and understanding will in turn enhance the resilience of Japanese citizens to possible nuclear coercion in the future.

Because of their (excessive) destructive power, nuclear weapons are not easy to use and therefore tend to function exclusively through psychological impacts in times of crisis or war. In recent years, the development of social media has made it impossible for elites and intellectuals to monopolize information, and the psychological effects of nuclear threats are likely to be amplified through social media. Therefore, it becomes imperative to educate the general public about the effectiveness and limits of nuclear weapons. For example, the utility of nuclear weapons as a coercive tool will be greatly reduced if Japan’s general public can say: “Since the threshold for actually using nuclear weapons is high, what North Korea is attempting to do is to deter military intervention by the United States and Japan,” or “China might threaten to use nuclear weapons, but China is not likely to use them against Japan because of the U.S. nuclear umbrella.”

While taking those steps, the United States and Japan must consider how to deal with the slim possibility of wartime use of nuclear weapons. The problem is, should China use nuclear weapons, it would do so against Taiwan or Japan and not against the United States. What should the United States and Japan do if China detonates a nuclear bomb near Okinawa to intimidate the Japanese government into neutrality? What should the United States and Japan do if China uses theater nuclear weapons to destroy or cause harm to a Japanese naval vessel in the Western Pacific? Unless the U.S.-Japanese alliance has some answers to these questions, China might be tempted to consider such actions.

Develop Closer U.S.-Japan-South Korea Policy Coordination

Since the end of the Cold War, two alliances—the U.S.-South Korea and U.S.-Japan alliances—have been devoted to the defense of South Korea. In the future, however, they will be required to deal with two theaters—the Korean Peninsula and the Taiwan Strait—instead of one. Moreover, the opponent that Japan would face across the Taiwan Strait would be the second-largest economy in the world. In that context, it will be essential to strengthen security cooperation among the United States, Japan, and South Korea; explore how roles, missions, and capabilities should be shared; and discuss how to make the best use of their limited defense resources.

Japan has decided to spend more on defense. However, given the two-theater commitment that it now makes, the security commitments that Japan—and the United States—can make to the defense of South Korea will likely decline in the future. Japan is already shifting its attention away from the Korean Peninsula toward the Taiwan Strait. Moreover, the United States might decide to commit some of its forces stationed in South Korea, especially air assets, to cross-strait contingencies. If that happens, the defensive resources that the United States and Japan could devote to the Korean Peninsula would further diminish. Some observers wish to see South Korea get militarily involved in a Taiwan contingency, but it is more likely that they will stay on the peninsula to deter an attack by North Korea.

The good news here is that South Korea has been making significant defense efforts in recent years. According to SIPRI, South Korea was the ninth-largest spender on defense in the world in 2022, allocating $46.4 billion, and its defense expenditure increased by 37 percent between 2013 and 2022. It has also acquired significant military capabilities, with more than 1,000 cruise and ballistic missiles. While it might be difficult for South Korea to directly contribute to Taiwan’s defense, it could do so indirectly. Since security on the Korean Peninsula and across the Taiwan Strait is becoming more intertwined, South Korea can make it possible for the United States and Japan to divert more military resources to the Taiwan Strait by playing a larger defensive role on the Korean Peninsula.

Therefore, the ongoing effort to strengthen trilateral security cooperation among the three countries must be continued and reinforced. In 2022, the three countries conducted a trilateral missile defense exercise near Hawaii and a trilateral anti-submarine warfare exercise in the Sea of Japan. Moreover, in October of the same year, the three countries’ leaders agreed to share North Korean missile warning data in real time to improve each country’s ability to detect and assess the threat posed by incoming missiles. Finally, on March 21, 2023, the South Korean government announced that the General Security of Military Information Agreement between Japan and South Korea would be fully implemented.

In the future, the United States, Japan, and South Korea should consider the following recommendations: First, they need to better coordinate their combined operation plans—​​​​​​​U.S.-South Korea OPLAN 5015 and U.S.-Japan OPLAN 5055—for possible Korean Peninsula contingencies. Although they are closely related, they are not well coordinated, largely due to the reluctance of past South Korean administrations. Second, the United States and Japan should take the defense of South Korea into account when they develop a new combined operation plan for a Taiwan contingency. That is essential given the increasing role that South Korea plays in regional security and the emerging two-theater nuclear threat that they face today. Finally, the three countries should start conducting combined exercises on air defense and non-combatant evacuation operations. The three allies and friends must work more closely together so that they can make the best use of the limited defense resources at hand.

Enhance the Transparency of Japan’s Legal Position on Preemption

One of the reasons why some experts remain suspicious about how Japan might use its strike capabilities comes from the lack of transparency in Japan’s legal position on preemption. Japan’s ostensibly restrictive position regarding preemption can make the country appear to be cheating on the issue.

While the Japanese government officially takes a position that preemptive strikes are illegal, it has suggested that the use of force very close to or even identical to preemption can be legal. In 2003, former defense minister Ishiba Shigeru said in the Diet that Japan could attack enemy missiles before they were launched if they were fueled and erected and if the enemy’s intention to attack Japan was evident. Ishiba said Japan’s action would not constitute preemption, but what he said sounded like it to many observers.

Japan’s allies and friends, including the United States and South Korea, regard preemption as legal and part of the right to (anticipatory) self-defense but regard prevention as illegal. It is ironic that by taking an ostensibly restrictive legal position regarding preemption Japan is making itself appear to be cheating.

To enhance the transparency of its policy and legal position, the Japanese government must either redefine the timing with which it could start using force or declare that it now regards preemption as legal—the position that the United Nations High-Level Panel on Threats, Challenges and Change took in 2004, for example. Some Japanese policymakers worry that Japan might appear aggressive by changing its position on the legality of preemption. However, manipulating the legal interpretation of international law for political and diplomatic purposes is not right. As discussed above, it is unlikely that Japan will conduct preemptive strikes due largely to geographical, military-technical, and policy reasons. If that is the case, the Japanese government must say so.

Michishita Narushige is executive vice president and professor at the National Graduate Institute for Policy Studies (GRIPS) in Tokyo.

The Strategic Japan initiative is made possible by a grant from the government of Japan.

Michishita Narushige

Executive Vice President and Professor, the National Graduate Institute for Policy Studies