AJISS-Commentary
The Association of Japanese Institutes of Strategic Studies
NPIRIPS

Nakasone Yasuhiro
Peace Institute

The Japan Institute ofInternational Affairs(Secretariat)

Research Institute for
Peace and Security

No. 305
16 October 2023

HOW SHOULD JAPAN CONSOLIDATETHE CREDIBILITY OF EXTENDED
DETERRENCE?
Nobumasa Akiyama
・ Russia’s use of nuclear threats during its invasion ofUkraine has undermined the confidence of Japan andSouth Korea in the US’s commitment to deter
nuclear-capable adversaries. As a result, Japan has
sought to bolster the credibility of extended nuclear
deterrence, opting for measures other than nuclear
sharing.
・ Beyond strengthening its “deterrence by denial”
through measures such as missile defense, Japan
seeks to build its own “deterrence by punishment”
capabilities by procuring its own stand-off missile
systems. These efforts aim to strengthen allianceassets capable of addressing threats under China’s
A2/AD environment.
・ Concurrently, it is imperative to pursue diplomatic
initiatives for threat reduction. Engaging in strategic
dialogue, especially discussions centered aroundcrisis management mechanisms to maintain stability
between China and the US-Japan alliance, will becrucial.
The views expressed in this piece are the author’s own and should not be
attributed to The Association of Japanese Institutes of Strategic Studies.

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The Association of Japanese Institutes of Strategic Studies

Shaken Confidence in Extended Deterrence
Russia’s invasion of Ukraine has given rise to the need for more in-depth
discussions of the role of nuclear weapons in Japan’s security, both in terms of theperceived threat posed by nuclear weapons and the effectiveness of the Japan-US
alliance’s extended nuclear deterrence.
The deployment of nuclear-capable missiles by Russia in its invasion ofUkraine, coupled with suggestive indications of potential nuclear weapon use, hasheightened awareness surrounding scenarios where a nuclear-armed nation seeks toassert dominance in a conflict by insinuating the employment of nuclear arms against aneighboring country. East Asian states have perceived the looming threat of a scenario
involving actual employment of nuclear weapons against them, alongside the potential
for more assertive actions by nuclear-armed states operating under the “nuclearshadow.”
As the likelihood of nuclear threats has escalated, there have been growing
voices in Japan and South Korea, both non-nuclear-weapon states, calling for greater
scrutiny of the credibility and reassurance that the United States offers through its
extended nuclear deterrence commitments, which are vital for both nations incountering nuclear threats. In Japan, momentum has been building, particularly amongconservative politicians following the lead of the late Prime Minister Shinzo Abe, for thepursuit of nuclear sharing with the US. The public tends to support discussions on
nuclear sharing, but they remain cautious in taking steps toward nuclear sharing,according to a poll by the Sankei Shimbun1. Meanwhile, in South Korea, support fordeveloping a nuclear arsenal has seen an upswing. According to a poll conducted by
the Chicago Council on Global Affairs and the Carnegie Endowment for International
Peace, approximately 70% of South Korean respondents supported their country having
its own nuclear arsenal2.
The debates in the two countries on how to ensure the credibility of extended
nuclear deterrence have once again demonstrated the need to consider two aspects:
the military utility of extended deterrence against security threats and the political effectof reassurance on the policy makers and citizens of allied countries.

1

https://www.sankei.com/article/20220321-HCS4IPTQKFPJBDV44EXPKSBZTE/

2

https://globalaffairs.org/research/public-opinion-survey/thinking-nuclear-south-korean-attitudes-nuclear-weapons

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Efforts to Enhance Extended Deterrence
To enhance the military effectiveness of extended deterrence, it is firstnecessary to assess the threats that the US’s allies face, understand the utility andlimitations of US nuclear deterrence in dealing with those threats, and build adeterrence architecture that appropriately combines nuclear forces with conventional
forces as well as cyber, ISR, and other assets.
On a strategic level, China has been augmenting its nuclear warhead count,with estimates projecting a total of 1,000 warheads by 2030. There will be more missiles
equipped as Multiple Independently-targetable Reentry Vehicles (MIRVs) that can belaunched from both silos and mobile platforms, heightening US vulnerability.
On a sub-strategic level, China possesses the capability to neutralize bases inJapan and Guam using intermediate-range ballistic missiles and cruise missiles,
effectively employing Anti-Access/Area Denial (A2/AD) strategies to inhibit US military
deployment in the region. Meanwhile, North Korea has consistently enhanced its
nuclear capabilities by advancing its missile technology and operational prowess. The
nation is developing what is termed “maneuverable tactical nuclear” capabilities and has
integrated nuclear weapons into its war-fighting arsenal on the Korean Peninsula.
In light of these developments, Japan needs to strengthen its “deterrence bydenial” and counterstrike capabilities to offset the offensive prowess of its adversaries,
with a special focus on trimming adversaries’ second-strike capabilities. Japan and theUnited States have already initiated the joint development of a new interceptor missile
to bolster their missile defense systems and complement ongoing endeavors to amplify
deterrence by denial. Japan has started to build its counterstrike capability, beginningwith the procurement of Tomahawk missiles from the United States, and it is alsoplanning the acquisition of standoff missile capabilities by extending the range ofexisting Type 12 surface-to-surface missiles (SSM). These weapons will also feature an
up-to-date command (UTDC) link that enables the missiles to obtain real-time target
updates during flight. Having been a party to the Intermediate-Range Nuclear Forces(INF) Treaty with the former Soviet Union, the United States lacks intermediate-range
missiles to incorporate into its regional escalation ladder, resulting in a power vacuum.
The long-range strike capability of Japan’s conventional warheads stands to fill this gap.
Enhancing Japan’s counterstrike ability will further elevate the threshold for adversaries
to initiate an attack. While Japan is accelerating its acquisition of stand-off missile
capabilities, Japan and the United States will have to live with vulnerabilities until they

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close the gap with China, which already possesses intermediate-range missile
capabilities.
It is also necessary to ensure asymmetric advantages at chokepoints inChina’s operations by integrating and operating assets in all domains, including
maritime, underwater, air, and cyber, so that China cannot achieve its strategic
objectives in a sustained manner. In particular, Japan and the United States should
ensure they maintain sufficient maritime and air capabilities to limit China’s ability tocarry out logistical supply operations across the Taiwan Strait.
Second, Japan and the United States need to collaboratively build the capacity
to effectively operate their assets. For instance, executing US military operations andproviding support in contingencies involving Taiwan or the Korean Peninsula would
prove extremely challenging without the support and joint action of Japan. It is crucial toproactively conceptualize the roles that Japan and the United States would undertake inscenarios where nuclear weapons, inclusive of nuclear threats, might be employed.
From China’s viewpoint, driving a wedge between Japan and the United States
could serve as an effective strategy to diminish US responsive capabilities in suchcontingency scenarios. It is plausible that nuclear threats against Japan could be
employed to achieve this objective, dissuading Japan from conducting joint operations
with the United States.
Addressing such risks necessitates the fortification of Japan-US coordinationand decision-making mechanisms within the framework of US-Japan extended
deterrence. Regularly conducted Extended Deterrence Dialogues (EDD) between
Japan and the United States foster a shared understanding and trust among
policymakers. Additionally, an Alliance Coordination Mechanism (ACM) has been
established. Building on this foundation, the alliance should contemplate scenarios
involving the use of nuclear weapons in integrated multi-domain situations such ascontingencies on Taiwan or the Korean Peninsula. It is imperative to establish
standardized procedures for information sharing regarding the US's use of nuclear
weaponsandtoexplore

mechanisms

for

joint

decision-making

andresponsibility-sharing concerning nuclear weapon employment.
Such an augmentation of the alliance’s operational posture would bolster theconfidence of politicians and the broader society in the alliance, contributing toenhanced reassurance. The bedrock of successful alliance operation is steadfast
political support.

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Diplomatic Efforts
Beyond making robust the deterrence architecture of the US-Japan alliance, itis essential to deepen and cement security cooperation with South Korea and Australia
as well as with Southeast Asian nations such as the Philippines and with India, whose
security interests are undermined by China’s assertive behavior. There should be aconcerted effort to enhance multilateral relations encompassing security, diplomacy,and economics to dissuade China from engaging in such behavior.
China should be kept from altering the status quo by force by making its
strategic calculations more complicated and getting it to recognize that its pursuit ofstrategic goals through coercive measures would prove excessively costly. This can beachieved by supporting capacity-building in neighboring countries and reinforcing theirresolve through strengthened political relations. It is imperative to acknowledge thatsuch efforts will not solely focus on “building the capacity” of neighboring nations. These
initiatives should contribute widely to the region’s sustainable growth and stability,extending beyond merely establishing a deterrence posture.
Pursuing dialogue with China and North Korea also makes sense from theperspective of threat reduction in the medium to long term. Although China has shownno interest in arms control and is pursuing military expansion for the time being, Japanand the United States should strive to convince China that arms control incorporates theelements of crisis management and confidence-building and serves all stakeholders’interests. In the midst of a confrontation between the United States and China, it isnecessary to have US-China strategic dialogue in order to avoid a situation in which
both sides misread the signals that each other’s actions send, leading to unintended
escalation of conflict (i.e., to ensure “crisis stability”).
Furthermore, in a situation where the stability of the US-China strategic
relationship is inseparable from the regional stability of the Indo-Pacific and where thedeterrence architecture also integrates the assets of non-nuclear allies such as missile
defense systems, ISR, and conventional strike capabilities with medium-range missiles,
the credibility of US extended deterrence in Japan could be significantly damaged if
Japan is perceived as being marginalized in the US-China strategic relationship.
Therefore, systematic and integrated strategic coordination dialogue between Japanand the United States on nuclear policy, covering topics ranging from deterrence andarms control to disarmament and nonproliferation, is necessary to avoid policy gaps
between the two countries. Such dialogue would also function as a sustained

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coordination mechanism allowing Japan and the United States to convey messages toChina and North Korea with one voice.

ConclusionIt goes without saying that extended deterrence arrangements with the UnitedStates are essential to Japan's security and need to be strengthened. What is required
now is an action plan the US and Japan, in cooperation with other partner countries, canswiftly implement to build assets comprising deterrence architecture, a coordination
mechanism for the US-Japan alliance to effectively operate assets optimized for the
threat landscape, and a solid political foundation. These efforts will be important toensure the credibility of extended deterrence and prevent China and North Korea frombelieving that changing the status quo by force is feasible. It will also be essential that
the United States, Japan, and other partner countries send closely coordinated andunified signals to China and North Korea to ensure that the pursuit of stability at thestrategic level between the United States and China does not create more room forcoercive behavior by China at the regional level in East Asia. At the same time, it will benecessary to engage in diplomatic efforts through strategic dialogue with China andNorth Korea to ensure crisis stability and build confidence that will lead to future arms
control.

AKIYAMA Nobumasa is a professor at Hitotsubashi University.

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