Japan’s Self-Defense Forces Trained in the Philippines. That Is How Much Japan Has Changed.

Japan’s Ground Self-Defense Force conducting joint amphibious training with Philippine military forces on Philippine territory represents a threshold that would have seemed extraordinarily difficult to cross just a few years ago. The Japan Times reported that the exercise took place in southern Philippines under the framework of the Reciprocal Access Agreement signed between Japan and the Philippines in 2024, allowing each country’s forces to train in the other’s territory. The legal and political barriers to Japanese forces operating in foreign territory for training purposes had been substantial. The fact that those barriers are being systematically dismantled through a series of bilateral agreements is one of the most concrete manifestations of Japan’s evolving security posture.

The rapid deepening of Japan-Philippines defense cooperation cannot be understood without reference to China’s intensifying activities in the South China Sea. China claims sovereignty over most of the South China Sea, including features well within the exclusive economic zones of Vietnam, Malaysia, Brunei, and the Philippines. An international arbitral tribunal ruled in 2016 that these claims had no basis in international law, but China has rejected the ruling and continued its activities. Chinese Coast Guard vessels have repeatedly interfered with Philippine fishing operations, used water cannons against Philippine supply vessels, and engaged in what the Philippine government characterizes as sustained harassment of vessels exercising rights within Philippine maritime zones. For the Philippines, Chinese maritime pressure is not an abstract geopolitical concern; it is a daily operational reality.

The Marcos administration’s sharp pivot from the pro-China orientation of the Duterte years has been consequential for regional security architecture. Rodrigo Duterte’s government had deliberately distanced the Philippines from its American alliance, pursued economic engagement with China, and downplayed maritime disputes. Ferdinand Marcos Jr.’s administration reversed this orientation: reinforcing the American alliance, granting American access to additional Philippine military facilities in strategically significant locations including Cagayan province facing Taiwan, and pursuing active security partnerships with Japan, Australia, and other partners. The policy reversal reflects not only different personal orientations but a genuine shift in Philippine military and political establishment threat assessment.

Japan’s interest in Philippines defense cooperation is significantly shaped by the geography of potential Taiwan contingencies. Taiwan lies immediately north of the Philippines, and any military conflict over Taiwan would involve the Philippine Sea and potentially affect Philippine territory or airspace. Japan’s own strategic planning for the defense of the Nansei Shoto island chain — the First Island Chain running through Okinawa, Taiwan, and the Philippines — requires understanding and coordinating with Philippine positions. An isolated Japan attempting to contribute to regional deterrence without Philippine cooperation would be strategically disadvantaged in ways that joint training and framework agreements are designed to address.

The Reciprocal Access Agreement represents a new category of Japanese security relationship with important implications for how Japan manages its regional defense commitments. Japan has concluded similar RAAs with Australia and is in negotiations with the United Kingdom, France, and other partners. Each agreement expands the geographic and functional scope within which the Self-Defense Forces can operate. The cumulative effect of these agreements is to create a Japan-centered network of bilateral defense relationships that functions as an informal multilateral security architecture — not a formal alliance like NATO, but a set of operational relationships that can be activated when circumstances require. Europe is undergoing its own parallel transformation — an 800 billion euro rearmament that marks the end of the postwar security order on that continent as well.

China’s criticism of the Japan-Philippines defense cooperation deepening is predictable in form but revealing in its logic. Beijing characterizes these arrangements as introducing outside powers into a regional dispute that should be resolved through direct bilateral negotiation — a framing that, whatever its merits as a diplomatic position, has become increasingly implausible given the scale of China’s own maritime activities. The countries whose maritime rights China is contesting have both the right and the legitimate reason to seek security partnerships with external parties. China’s objection to American, Japanese, and Australian involvement in Southeast Asian security cannot be separated from the Chinese activities that are driving that involvement. These security tensions exist alongside deep economic uncertainty — China may be entering its own lost decade, a development that could reshape the strategic calculus for every country in the region.

The United States has actively encouraged and facilitated this network of bilateral security relationships as part of its broader Indo-Pacific strategy. The Biden administration’s convening of the first US-Japan-Philippines trilateral summit established a formal framework for three-way security cooperation. This framework has been sustained under the Trump administration, reflecting a degree of continuity on alliance management questions that is not always visible given the Trump administration’s rhetorical style. The integration of Japan and the Philippines into a common deterrence framework with the United States gives each party greater confidence in the collective response to Chinese coercive activities.

ASEAN’s internal divisions complicate the development of a coherent regional response to Chinese maritime assertiveness. The organization operates on a consensus basis, meaning any single member’s reluctance — Cambodia and Laos maintain notably close relationships with China — can prevent the development of strong collective positions. Individual ASEAN members like the Philippines and Vietnam, which face the most direct Chinese pressure, have been forced to pursue bilateral partnerships outside the ASEAN framework to address immediate security needs. This dynamic fragments the regional security architecture in ways that China finds advantageous and that make comprehensive multilateral solutions difficult to construct.

Japan’s parallel investment in coast guard capacity building for the Philippines addresses a different dimension of the same problem. The interactions between Chinese Coast Guard vessels and Philippine supply and patrol vessels operate in legal and escalatory gray zones where military responses would be inappropriate but where the Philippines needs enhanced capability to document, respond to, and resist Chinese pressure. Japanese assistance in building Philippine Coast Guard capacity — vessels, equipment, training — enables Manila to respond to routine coercive activities without triggering the military escalation ladder that direct SDF-PLA interactions would involve. This layered approach, combining military deterrence at the high end with law enforcement capability at the operational level, represents a sophisticated response to the graduated coercion problem.

Japan’s expanded defense budget provides the financial foundation for these cooperative activities to be sustained at meaningful scale. Equipment transfers to the Philippines, the logistics infrastructure required for SDF overseas training, the ongoing costs of joint exercises — all of these require defense budget capacity that Japan’s previous one-percent-of-GDP constraint did not provide. The security cooperation that Japanese officials had long discussed as desirable but difficult to fund is becoming operationally real because of the budget increases that have changed the resource constraint.

The broader Japan-Philippines relationship provides a stable foundation for the expanding security dimension. Japan has been among the largest ODA donors to the Philippines for decades, with deep cooperation in infrastructure, agriculture, education, and disaster risk reduction. The trust built through decades of development partnership creates a context in which security cooperation can develop without the suspicion that might attend a purely transactional military relationship. Japan’s preference for comprehensive partnerships that integrate economic, developmental, diplomatic, and security elements reflects both strategic calculation and an institutional preference for engagement over pure power projection.

The optimistic scenario has Japan-Philippines security cooperation functioning as intended — as a component of a credible deterrence architecture that changes China’s cost-benefit calculation for coercive activities. If regional military posture becomes sufficient to make Chinese attempts at controlled escalation in the South China Sea or against Taiwan militarily risky and diplomatically costly, the calculus favoring restraint grows stronger. Stable deterrence enables commerce, including the vast volume of Japanese trade that transits the South China Sea, to continue without interference. Over time, the existence of credible deterrence might create conditions for the kind of maritime governance negotiations that have been difficult to initiate in the current environment of Chinese confidence.

The pessimistic scenario involves inadvertent escalation from the multiple overlapping activities in the South China Sea. Chinese Coast Guard vessels, Philippine supply ships, American naval patrols, Japanese training exercises, and commercial fishing fleets all operate in close proximity in contested waters. A collision, an aggressive maneuver that results in casualties, or a miscalculated warning shot could trigger an escalatory sequence that none of the parties intended. The presence of more players with clearer mutual commitments reduces some risks while potentially increasing others — the Japan-Philippines RAA means that an incident involving either party could draw the other in under circumstances that neither had specifically anticipated.

Japan is discovering, through the practical experience of building these security partnerships, that the diplomatic work of maintaining deterrence is as demanding as the military capability it requires. Ensuring that China understands the defensive intent of joint training arrangements requires sustained communication and reassurance alongside capability development. Managing the expectations of alliance partners about what Japan will and will not do in various contingency scenarios requires careful signaling. Balancing security commitments to the Philippines and others with the need to maintain working diplomatic relationships with China — Japan’s largest trading partner — requires ongoing judgment calls about tone and substance that cannot be reduced to simple rules.

The South China Sea, for Japan, is ultimately an economic security issue as much as a military one. A substantial portion of Japan’s trade passes through these waters, and Chinese control over the sea lanes connecting Japan to Southeast Asian markets, Middle Eastern energy suppliers, and beyond would create a strategic vulnerability comparable in kind to the Hormuz Strait dependence this week’s analysis also addresses. The defense of open sea lanes is not abstract strategic theory for Japan; it is a practical requirement of economic functioning. Japan-Philippines security cooperation, seen from this perspective, is not just about preventing Chinese military action against Taiwan; it is about preventing the conditions under which Japan’s economic lifelines could be subject to Chinese interdiction.

The strategic significance of Philippine geography extends well beyond the Taiwan Strait contingency that dominates discussions of Japan-Philippines security cooperation. The Philippines sits at the intersection of the Pacific Ocean and the sea lanes connecting Northeast Asia with Southeast Asia, the Indian Ocean, and ultimately with Middle Eastern energy suppliers. Control or disruption of Philippine maritime zones would affect Japanese commerce in ways that have no easy alternative routing — unlike the Hormuz Strait, which can at least theoretically be bypassed at great cost via the Cape of Good Hope, there is no alternative routing for traffic between Japan and Southeast Asia that doesn’t involve Philippine waters. This geographic reality gives Japan an economic security interest in Philippine maritime stability that exists independently of alliance commitments and Taiwan contingency planning.

The trilateral US-Japan-Philippines security framework represents one of the more consequential institutional innovations in Indo-Pacific security architecture of recent years. The framework formally established at the 2024 trilateral summit provided a venue for three-way coordination that previously had to be managed through separate bilateral relationships. Joint planning, information sharing arrangements, and coordinated responses to Chinese coercive activities in the South China Sea have been developed within this framework with a specificity that bilateral relationships alone would not produce. The fact that the Trump administration has maintained this framework despite its general preference for transactional bilateral arrangements suggests that the framework’s value for American strategic purposes is recognized even when alliance solidarity is not the primary American motivation.

The economic dimensions of Japan’s defense cooperation with the Philippines extend beyond defense equipment transfers to encompass infrastructure investment that serves dual civilian and security purposes. Japanese ODA-funded port developments, airfield improvements, and communications infrastructure in the Philippines provide civilian development benefits while also improving the logistical foundation for security cooperation. This dual-use dimension of Japanese infrastructure investment is consistent with Japan’s preference for comprehensive engagement over narrow transactional security arrangements, and it reflects an understanding that durable security partnerships require broad-based relationship investment rather than episodic military cooperation. The long history of Japanese development cooperation with the Philippines provides a foundation of relationships and institutional knowledge that purely military-to-military engagements cannot replicate.

China’s response to the strengthening Japan-Philippines security relationship has been primarily rhetorical rather than substantive, which itself reveals something about China’s strategic calculations. Beijing has condemned the arrangements as destabilizing provocations, accused the Philippines of serving as a tool of external powers, and characterized Japan’s involvement as evidence of remilitarization. But China has not taken concrete retaliatory action against either Japan or the Philippines that would impose specific costs for the security cooperation, suggesting that Chinese leadership has assessed that the benefits of escalating to coercive responses are outweighed by the costs. This does not mean Chinese tolerance is unlimited, but it does suggest that the security cooperation has been calibrated within a range that China accepts as manageable even while objecting to it rhetorically.

The ASEAN principle of centrality — the insistence that ASEAN must remain the center of regional security architecture rather than being superseded by external power frameworks — creates a diplomatic context that Japan must navigate carefully as its bilateral security engagements deepen. Most ASEAN members support neither Chinese nor American dominance and regard the deepening of Japan-Philippines security cooperation with a mixture of strategic appreciation and institutional concern. Framing Japan’s activities as consistent with ASEAN processes, contributing to maritime law enforcement capacity rather than only military deterrence, and maintaining dialogue with China through ASEAN forums alongside bilateral security engagement, allows Japan to pursue its security interests while preserving the regional institutional architecture that gives smaller ASEAN states a degree of agency they would lose in a purely great power competition framework.

The experience of joint training operations reveals practical challenges in interoperability that must be managed for cooperation to be operationally effective rather than merely symbolically significant. Differences in communication systems, operational procedures, doctrinal approaches, and equipment standards between Japanese SDF and Philippine armed forces create real constraints on the operational effectiveness of joint operations. The purpose of exercises like the one reported by the Japan Times is partly to identify and address these interoperability gaps — standardizing procedures, building personal relationships between counterpart units, and developing the mutual understanding of each other’s capabilities and limitations that operational coordination requires. This practical dimension of military cooperation, less visible than the political agreements that enable it, is ultimately what determines whether declared security commitments translate into effective crisis responses.

The institutional development required to make the Japan-Philippines security relationship operationally effective is a longer and more difficult process than the agreements and exercises that mark its public milestones suggest. Creating genuine military interoperability — the ability to coordinate operations under stress, share intelligence in real time, and sustain combined operations logistically — requires years of sustained engagement at the unit level, not just periodic high-profile exercises. The SDF and the Armed Forces of the Philippines must develop shared operational procedures, compatible communications systems, and the mutual professional understanding that allows different militaries to function as a coherent force when the pressures of a real crisis compress decision timelines. This practical foundation of interoperability is less visible than the political agreements but ultimately determines what the security relationship can actually accomplish.

The intelligence sharing dimension of Japan-Philippines security cooperation, while rarely discussed publicly, is one of the most practically significant aspects of the relationship. Japan’s surveillance assets — including maritime patrol aircraft, satellites, and the expanded intelligence collection capabilities funded by recent defense budget increases — provide a persistent picture of Chinese maritime activities in the South China Sea and its approaches that the Philippines cannot independently develop. Sharing this intelligence enables Philippine security forces to respond to Chinese activities with better situational awareness and more effective positioning. The intelligence relationship also creates incentives for Philippines to protect Japanese interests, as the value of Japanese intelligence sharing depends on the Philippines treating that information responsibly — creating a form of mutual dependence that reinforces the security partnership’s durability.

The maritime law enforcement cooperation between Japan Coast Guard and the Philippine Coast Guard represents a model of security cooperation that other Indo-Pacific partners are watching closely as a potential template. Providing vessels, training, and operational support for law enforcement activities that fall below the military force threshold allows partner countries to respond to Chinese gray zone activities without triggering the military escalation risks that SDF-PLA interactions would involve. This approach is consistent with the international law framework governing maritime disputes: Coast Guard interactions operate under different legal frameworks than military confrontations, potentially providing more flexibility to document and resist Chinese activities in ways that build an evidence record for international legal proceedings while avoiding the escalatory risks of direct military confrontation.

The long-term evolution of the Japan-Philippines relationship will be shaped significantly by Philippine domestic politics, which are less stable and predictable than the current policy trajectory suggests. Philippine elections produce significant foreign policy shifts, as the transition from Duterte’s China-leaning posture to Marcos’s pro-alliance orientation demonstrated. A future Philippine administration that decided to reprioritize economic relations with China over security partnerships with Japan and the United States could quickly reverse the institutional progress of the current period. Japan’s investment in the relationship therefore needs to extend beyond government-to-government security arrangements to include economic partnerships, development assistance, and people-to-people connections that create constituencies for the relationship’s continuation regardless of which political party is in power.

The quadrilateral dimension of Indo-Pacific security cooperation — Japan, the United States, Australia, and India — creates a framework within which Japan-Philippines cooperation can be understood as one element of a broader security architecture rather than a purely bilateral arrangement. Australia’s growing security engagement with Southeast Asia, India’s expanding maritime presence in the Indian Ocean and its eastern approaches, and American naval activity across the region collectively create a security environment that China must navigate with multiple capable actors rather than a single dominant American presence. Japan’s bilateral security partnerships with the Philippines and others contribute to this broader architecture while also providing specific local deterrence value. The layered nature of the security architecture — bilateral, trilateral, quadrilateral, and broader coalitional arrangements — makes it more resilient to any single relationship’s disruption.

China’s response to the strengthening of Indo-Pacific security partnerships will be a key variable in determining whether these arrangements produce stable deterrence or escalating security competition. If China interprets the Japan-Philippines security cooperation and the broader network of partnerships as evidence of an encirclement strategy aimed at Chinese regime security rather than regional maritime law enforcement, its responses will be more aggressive and destabilizing than if it interprets them as defensive measures aimed at deterring specific coercive behaviors. Chinese leadership’s actual interpretation of these arrangements — as opposed to the rhetorical condemnations issued for domestic audiences — shapes the operational decisions of Chinese coast guard and naval commanders in the South China Sea. Maintaining channels of communication that convey defensive intent to Chinese military professionals, separate from the political communication channels that are constrained by domestic political requirements on both sides, is an important but difficult task for both Japan and the United States.

The economic integration of the Philippines into regional supply chains — accelerated by Japanese corporate investment, American trade relationships, and the Philippines’ growing manufacturing and services sectors — creates mutual economic interests that reinforce the security relationship. Japanese companies have been among the largest foreign investors in the Philippines across multiple sectors including electronics, infrastructure, retail, and financial services. This investment creates employment, technology transfer, and economic linkages that give both countries’ private sectors a stake in the stability of the bilateral relationship independent of government policy decisions. The economic interdependence does not eliminate security tensions, but it creates constituencies on both sides for managing them constructively and provides a positive dimension of the relationship that pure security partnerships lack.