September 13, 2023

Strengthening the Shield

Japan’s Defense Transformation and the U.S.-Japan Alliance

Executive Summary

In December 2022, Japan’s government released three major strategic documents: the National Security Strategy, the National Defense Strategy, and the Defense Buildup Program. Although Japan has made incremental changes to its security policies and capabilities over the last decade, the new documents mark a notable shift in Japan’s approach to strengthening its defense. The documents reflect Tokyo’s assessment of the rising threats that could challenge Japan’s security and signal Japan’s commitment to build the military capabilities necessary to meet them. This report examines Tokyo’s defense transformation and assesses its implications for the U.S.-Japan alliance and Washington’s strategy toward the Indo-Pacific.

Japan is “fundamentally reinforcing” its national security and defense policies to cope with its increasingly severe security environment. The military threats posed by China, North Korea, and Russia have been growing steadily for years but appear to be peaking simultaneously. Tensions between Japan and China have occasionally flared in the five decades since they normalized diplomatic relations. But those tensions have reached new heights since 2012, when China began to regularly contest Japan’s administration of the Senkaku/Diaoyu Islands. By August 2022, Beijing fired five ballistic missiles into Japan’s exclusive economic zone during China’s live-fire military exercises after then-U.S. House Speaker Nancy Pelosi’s visit to Taiwan. The aim of the missile launches was to signal there would be consequences for Japan if Tokyo were to intervene in a Taiwan contingency. Meanwhile, North Korea’s unprecedented rate of missile testing since 2022 and Russia’s brutal war against Ukraine have deepened Japanese concerns about the potential for the use of force in the Indo-Pacific.

Japan is taking steps to improve its ability to defend itself and deter an invasion, including through changes to security funding and policy. Tokyo has announced plans to increase its defense spending by 65 percent over the next five years, acquire standoff weapons that could be used for a counterstrike mission, and adopt an “active cyber defense” posture. Japan has clarified the roles of its military, the Self-Defense Forces (SDF), and Coast Guard in the event of an attack; committed to establishing a permanent Joint Headquarters for SDF operations; and created a program for supplying partner militaries with security assistance. Effectively employing counterstrike and active cyber defense, however, will require a clearer delineation of the legal authorities for their use as well as the overall military strategies that they would support. In addition, pressure from the Japanese public over tax hikes required to pay for the defense spending increase amid other fiscal pressures could pose a barrier to implementation.

Japan plans to strengthen the SDF through boosting readiness and resilience of current forces, acquiring counterstrike and other advanced capabilities, and improving force posture and mobility. The SDF has been plagued by a chronic lack of munitions and other supplies, and most of its facilities do not meet its own standards for resilience against enemy attack. Addressing these shortfalls is essential, though these types of programs often lose out to more high-profile programs. For its counterstrike mission, Japan has announced it will buy U.S.-made Tomahawk cruise missiles. This initial purchase will provide a stopgap until Japan is able to produce its own longer-range missiles later in the decade. Japan has also announced it will pursue new capabilities in uncrewed systems, space, cyber, and artificial intelligence (AI). But fulfilling these ambitions will be challenging given some short-falls in Japan’s technology base and SDF personnel. Lastly, the SDF is grappling with how to expand its forces in Japan’s southwest islands while maintaining a sufficient presence throughout the country to deter aggression from a range of possible threats.

Next, Japan’s strategy emphasizes enhancing security partnerships regionally and across the globe. Japan has recently stepped up its defense cooperation with several Indo-Pacific and European countries. With Australia, Japan is building on a 10-year effort to deepen strategic cooperation, a process that culminated in January 2022 with the completion of a Reciprocal Access Agreement. New bilateral strategic cooperation includes enhancing interoperability between the SDF and the Australian military, increasing rotational SDF training deployments to Australia, and announcing a new joint security declaration that commits to a combined response to military contingencies. Similarly, Japan has long recognized the strategic importance of India and continues to build on the Japan-India relationship through maritime security cooperation, a new joint fighter exercise, and operationalization of their Acquisition and Cross-Servicing Agreement.

Japan and the Philippines are also expanding their defense ties through humanitarian assistance and disaster relief training exercises and an important emerging trilateral security relationship with the United States. Over the past year, Japan and South Korea have made significant strides to repair relations since the latest downturn that began in 2018. This will be an incremental process, but there has been progress in the form of leader-level summits and ministerial dialogues, plans to cooperate on sharing data about North Korean missiles, and new trilateral ballistic missile and anti-submarine drills with the United States. Japan also is building defense connections and relationships with European nations. It is pursuing the development of a sixth-generation fighter jet with the U.K. and Italy and, particularly since the full-scale Russian invasion of Ukraine, has sought to deepen strategic ties with NATO.

These comprehensive changes to Japan’s defense policies will necessarily reshape the military and security pillars of the U.S.-Japan alliance. Tokyo’s acquisition of counterstrike capabilities will position Japan to potentially take on some offensive tasks, even while retaining its primarily defensive orientation. This also has implications for alliance contingency planning related to defending Japan directly as well as around Taiwan, the Korean Peninsula, and the South China Sea. However, increased joint planning will require updates to alliance command and control (C2) and information-sharing mechanisms. Additionally, given resource constraints, the alliance would be well-served to find additional opportunities for military technology sharing, codevelopment, and coproduction, such as through Japanese involvement in the second pillar of the AUKUS (Australia-United Kingdom-United States) partnership focused on cooperation on advanced capabilities and defense technology innovation. And the alliance must take steps to improve force posture and readiness, including through enhancing base resiliency and increasing munitions stockpiles.

Japan’s fundamental transformation of its defense posture will mean significant changes for the U.S.-Japan alliance. The United States must adapt its approach to alliance coordination to maximize new opportunities and manage any new challenges. In this context, U.S. policymakers should:

  • Prepare to update the alliance, while recognizing that Japan’s new defense policies will require significant time, resources, and political will to implement.
  • Stay closely aligned with Tokyo on the threat land- scape as well as engagement with geopolitical competitors, especially China.
  • Integrate U.S.-Japan command and control structures.
  • Create an alliance readiness, resilience, and posture implementation task force.
  • Deepen planning for contingencies and bolster extended deterrence.
  • Create a road map for expanding defense technology cooperation concurrently with Japan’s implementation of specific improvements to its information security practices and infrastructure.
  • Innovate operational concepts for uncrewed systems and counterstrike capabilities.
  • Leverage the U.S.-Japan alliance as a hub for minilateral and multilateral security engagement.
  • Build U.S.-Japan alliance mechanisms that will expand cooperation on cyber security and defense.
  • Stand up an alliance dialogue on military personnel issues.


Japan’s national security and defense policies are undergoing a period of profound transformation. Mounting threats from the People’s Republic of China (PRC or China), the Democratic People’s Republic of Korea (DPRK or North Korea), and the Russian Federation (Russia) have led Tokyo to conclude it is “facing the greatest post-war trial yet, and has entered into a new era of crisis.” To “squarely face the grim reality and fundamentally reinforce Japan’s defense capabilities,” last December Prime Minister Kishida Fumio’s administration released three major documents—the National Security Strategy, the National Defense Strategy, and the Defense Buildup Program— that together outline an ambitious plan to overhaul the country’s defense policies and military forces over the next decade.

Some of the changes articulated in those documents are evolutionary shifts that build on more than a decade of incremental steps to improve the ability of the Self- Defense Forces (SDF), Japan’s military, to protect the country in the face of intensifying security threats. Other parts of the vision Japan laid out in the three strategic documents, though—such as acquiring counterstrike weapons and adopting an active cyber defense policy—constitute revolutionary changes in Tokyo’s approach to security. Taken together, Japan plans to retain its long-standing “exclusively national defense-oriented policy” while revising key tenets of how Tokyo interprets and implements that policy. This new approach heralds Japan’s latest and most ambitious step in a decades-long journey away from the post-World War II grand strategy associated with former Prime Minister Yoshida Shigeru, in which the country forswore a strong military and relied heavily—too much, some argued—on the United States for its security.

This report examines Japan’s evolving defense policy and assesses the implications for the U.S.-Japan alliance and Washington’s strategy toward the Indo-Pacific. It focuses on defense policy while acknowledging that Japan envisions using all the tools of its “comprehensive national power”—including diplomacy, technology, economics, and intelligence—to achieve its foreign policy objectives. Now, nearly nine months since the release of those documents, it is possible to begin to assess prospects for implementation as well as emerging obstacles that could undermine the strategy.

The report begins by taking stock of Japan’s increasingly severe security environment, with a focus on the threats from China, North Korea, and Russia. The next section details changes to Tokyo’s military spending and defense policies. Then the report explores capabilities and force posture shifts. The subsequent two sections evaluate how these changes are shaping Japan’s security partnerships and then assess implications for the U.S.-Japan alliance. Finally, the report offers recommendations for policymakers in Washington for how to leverage these trends to strengthen the U.S.-Japan alliance, deter aggression, and protect peace and stability in the Indo-Pacific region.

Read the Full Report

Download PDF

  1. Japan Ministry of Defense, National Defense Strategy (December 16, 2022; provisional English translation as of December 2022), 4,
  2. Quotation from Japan National Defense Strategy, 4. The three documents are: National Security Council of Japan, National Security Strategy of Japan (December 16, 2022; provisional English translation as of December 2022),; Japan Ministry of Defense, National Defense Strategy; and Japan Ministry of Defense, Defense Buildup Program (December 16, 2022; provisional English translation as of March 14, 2023),
  3. For background on the Yoshida Doctrine, see Tobias Harris, The Iconoclast: Shinzo Abe and the New Japan (London: Hurst Publishers, 2020),; Michael J. Green, Line of Advantage: Japan’s Grand Strategy in the Era of Abe Shinzō (New York: Columbia University Press, 2022),; Jennifer Lind, “Japan Can’t Pass the Buck Anymore,” The New York Times, May 18, 2023,; and Yusuke Ishihara, “Japan’s grand strategy as a declining power,” East Asia Forum, June 18, 2023,
  4. National Security Council of Japan, National Security Strategy of Japan, (provisional English translation), 11-12.


  • Jacob Stokes

    Senior Fellow, Indo-Pacific Security Program

    Jacob Stokes is a Senior Fellow for the Indo-Pacific Security Program at CNAS, where his work focuses on U.S.-China relations, Chinese foreign and military policy, East Asian ...

  • Lisa Curtis

    Senior Fellow and Director, Indo-Pacific Security Program

    Lisa Curtis is a Senior Fellow and Director of the Indo-Pacific Security Program at CNAS. She is a foreign policy and national security expert with over 20 years of service in...

  • Joshua Fitt

    Former Associate Fellow, Indo-Pacific Security Program

    Joshua Fitt is a former Associate Fellow for the Indo-Pacific Security Program at CNAS. He focuses on U.S. East Asian security strategy and specializes in Japanese and Korean ...

  • Lieutenant Colonel Joseph I. Grimm

    Former Senior Military Fellow, United States Marine Corps

    Lieutenant Colonel Joseph I. Grimm is a Commandant of the Marine Corps’ Fellow at the Center for a New American Security (CNAS) in Washington, D.C. LtCol Grimm recently comple...

  • Rebecca Wittner

    Former Research Consultant, Indo-Pacific Security Program

    Rebecca Wittner is a former research consultant and former Joseph S. Nye, Jr. intern for the Indo-Pacific Security Program at the Center for a New American Security (CNAS). Sh...

View All Reports View All Articles & Multimedia