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Defense leaders from the United States, Australia, Japan, and the Philippines met in Singapore at the sidelines of the Shangri-La Dialogue 2025 to reaffirm their shared commitment to a “free and open Indo-Pacific” amid escalating concerns over China’s activities in the region.

This meeting marked the fourth time the four nations’ defense chiefs have convened in the past three years, reflecting the urgency and consistency of their strategic alignment in response to evolving regional challenges.

Australian Deputy Prime Minister and Minister for Defense Richard Marles, Japanese Minister of Defense Nakatani Gen, Philippine Secretary of National Defense Gilberto Teodoro, Jr., and United States Secretary of Defense Pete Hegseth participated in the high-level dialogue. A joint statement was released at the end of the meeting emphasizing cooperation, deterrence, and adherence to international law.

“This meeting reaffirms our shared vision for a free and open Indo-Pacific,” the ministers declared, citing continued “serious concern about China’s destabilizing actions in the East China Sea (ECS) and the South China Sea (SCS)” and voicing opposition to “any unilateral attempts to change the status quo by force or coercion.”

Reiterating commitment to the rule of law

The statement strongly reaffirmed the importance of upholding international law, particularly as reflected in the United Nations Convention on the Law of the Sea (UNCLOS), and stressed the principles of freedom of navigation and overflight in contested areas. The leaders condemned “dangerous conduct by China in the SCS against the Philippines and other countries,” while calling for the peaceful resolution of disputes.

This latest warning reflected the increasing frustration over Chinese maritime activities, including the recent escalation between Chinese and Filipino vessels near Second Thomas Shoal and assertive moves in disputed waters around the Senkaku/Diaoyu Islands.

The four defense ministers also reiterated their support for the Association of Southeast Asian Nations (ASEAN), emphasizing its “central role” in fostering regional peace and stability.

Four pillars of strengthened defense cooperation

During the summit, the leaders unveiled four key developments that will further deepen the quadrilateral security cooperation and bolster the collective defense posture in the Indo-Pacific:

Synchronizing priority defense investments

A core outcome of the summit was the agreement to align infrastructure investments and defense initiatives, particularly in the Philippines, a frontline state increasingly facing Chinese pressure in the SCS.

“Together, the installation of Japan-made air surveillance radar systems at Wallace Air Station, the United States’ continued development and integration of air domain sensors at Basa Air Base Command and Control Fusion Center, and Australia’s efforts to support the growing defense infrastructure in the Philippines have collectively helped improve the Armed Forces of the Philippines’ air domain awareness in the SCS,” the statement noted.

Enhancing information-sharing

The leaders recognized the need for greater intelligence collaboration to build a common operating picture in the South China Sea and beyond. A major step forward came with the recent conclusion of a bilateral General Security of Military Information Agreement (GSOMIA) between the U.S. and the Philippines, an agreement that facilitates the secure exchange of sensitive defense information.

Australia and Japan announced intentions to pursue similar GSOMIA agreements with the Philippines. The goal is to eventually integrate these efforts at a combined intelligence hub, where real-time data-sharing and collaborative analysis can take place.

My first bilateral meeting at the 2025 Shangri-La Dialogue was with @SecDef, our second catch up since he stepped into the role earlier this year.

We discussed avenues for further economic and security cooperation, and our unwavering commitment to the Indo-Pacific. pic.twitter.com/NAoLPx53te

— Richard Marles (@RichardMarlesMP) May 30, 2025

Strengthening cybersecurity and resilience

The ministers also agreed to jointly invest in cyber defense capabilities for the Philippines, acknowledging the growing threat posed by malicious cyber actors in the region. These investments will be channeled through existing defense exercises and training programs, aimed at bolstering both institutional and technical resilience against intrusions.

While not publicly attributing specific cyberattacks to China, the move underscores the growing importance of cybersecurity as a key pillar of modern defense cooperation.

Increasing operational coordination and interoperability

Perhaps the most consequential outcome of the meeting was the pledge to deepen operational coordination through joint exercises, maritime patrols, and intelligence-sharing activities in both the East China Sea and South China Sea.

“They committed to sustaining their participation and expanding the scope and frequency of such engagements with additional like-minded partners,” the statement read.

Additionally, the four nations reached consensus on planning joint intelligence, surveillance, and reconnaissance (ISR) operations, which will improve interoperability and contribute to deterrence by maintaining a persistent presence and situational awareness in disputed waters.

Regular engagement and a long-term vision

The ministers emphasized the importance of institutionalizing regular engagements at both the ministerial and working levels, ensuring that coordination does not wane amid shifting political dynamics. This continuity, they agreed, is essential to maintaining credibility, readiness, and regional trust.

“Looking ahead, they committed to continue working together and with other like-minded partners to support peace, stability, and prosperity in the Indo-Pacific.”

Strategic Context and Future Implications

The timing of this joint statement is notable. It comes just weeks after heightened Chinese activity around Taiwan and persistent confrontations with Filipino resupply missions in the Spratly Islands. It also follows increased U.S. military presence in the region, including rotational deployments in northern Australia and the Philippines under the Enhanced Defense Cooperation Agreement (EDCA).

Analysts see this quadrilateral format, distinct from the QUAD alliance (composed of the U.S., India, Japan, and Australia), as a more operationally focused framework built specifically around real-time regional threats, especially in the maritime domain.

With China’s maritime assertiveness unlikely to recede, observers believe this defense coordination will not only expand but potentially draw in other partners such as South Korea, the United Kingdom, or even ASEAN members willing to align more closely with the U.S.-led order.

As geopolitical tensions continue to roil the Indo-Pacific, this summit in Singapore represents a pivotal moment in the consolidation of an emerging defense architecture. By aligning resources, deepening operational ties, and openly addressing Chinese coercion, Australia, Japan, the Philippines, and the United States are signaling both resolve and unity in defense of shared values.

While the road ahead remains uncertain, one thing is clear: the Indo-Pacific is now the frontline of strategic competition, and this four-nation partnership is increasingly at its core.