By Focus | 2025-10-30

Philippine and US Marines recently staged a major exercise to defend Balabac Island, a gateway between the Sulu and South China seas, underscoring Manila's effort to strengthen its southern defenses.

The two-week exercise, Marine Air Support Activity 2025 (MASA 25), concluded on October 24 after a series of complex drills that included coastal defense and maritime strike operations, military free fall, helicopter underwater escape training and subject-matter-expert exchanges, ABS-CBN News reported.

MASA is an annual Philippine-US drill focused on enhancing aerial and maritime interoperability.

Manila plans to build a military base on Balabac, the westernmost undisputed island in the Philippines. Lying just 50km north of Malaysia, the island commands the Balabac Strait, a vital waterway linking the Sulu Sea and the South China Sea, which Manila refers to as the West Philippine Sea.

During the exercise, Philippine Coast Guard (PCG) special forces and Philippine marines conducted joint maritime boarding operations near Balabac.

The boarding drill aimed to "prevent hostile forces from establishing a foothold in the vicinity" of Balabac Island, according to a PCG statement.

The Philippine navy said a high-altitude insertion exercise, which dropped force reconnaissance marines onto Balabac, demonstrated the marines' ability to seize objectives in a "contested littoral environment," USNI News reported.

Leveraging new capabilities

MASA 25 took place across several locations in Northern Luzon (Ilocos Norte), Central Luzon (Zambales), the National Capital Region (Cavite and Taguig City) and Palawan, according to the Philippine Marine Corps (PMC).

The drills involved 524 personnel from the PMC and 130 from the US Marine Corps (USMC), as well as marine reservists and personnel from the Philippine Air Force-Naval Air Wing and the PCG.

USMC Col. Robb McDonald, commanding officer of the US Marine Rotational Force -- Southeast Asia, emphasized the importance of the drill in improving the two forces' ability to respond to emerging security challenges.

"That is what MASA is all about: a focus on leveraging new capabilities and emerging concepts, especially as they relate to maritime defense, and striking hard at threats," McDonald said during the closing ceremony at Naval Station Jose Francisco in Taguig City. "By training together, we enhance regional stability and security for a free and open Indo-Pacific."

The "level of proficiency and interoperability we achieved between our forces has been exemplary," he said, according to ABS-CBN News.

As part of the training, PMC and USMC communication units worked together to master Tactical Awareness Kits (TAK), a real-time digital situational tool.

"Together, we were able to instantly share digital information security across networks and radios," McDonald said. "The use of this technology throughout the exercise validated how effective they could be."

Importance of Balabac

Balabac Island is one of nine sites selected under the Enhanced Defense Cooperation Agreement (EDCA), which allows US-funded facilities and rotational troop deployments in the Philippines.

Signed in 2014, the EDCA supports the training, humanitarian response and modernization of Philippine forces.

The two sides chose Balabac as an EDCA site in 2023.

It is the only one touching the South China Sea. Using it for Philippine–US military cooperation reflects rising tensions between Manila and Beijing.

The Philippine government has invested heavily in Balabac, upgrading an existing littoral monitoring station, building a 3km-long military runway and expanding the Narcisco Del Rosario Naval Station with a pier capable of accommodating destroyer-sized ships. These projects predate the EDCA.

Complementing the military upgrades, the Philippine Department of Energy, through the National Power Corporation and the Armed Forces of the Philippines, delivered a Mobile Energy System (MES) to the island on October 3. The MES, housed in a 20-foot-long trailer, includes solar panels, a hybrid inverter and battery storage to provide off-grid power for command centers, hospitals and emergency facilities. The project is part of the US-funded Energy Secure Philippines program.

Supporting laws

Last November, the Philippines enacted two maritime laws aimed at reinforcing its sovereignty in the South China Sea. The Philippine Maritime Zones Act defines the country's territorial waters and Exclusive Economic Zone, while the Philippine Archipelagic Sea Lanes Act regulates foreign vessel transit through its waters. Both align national law with the United Nations Convention on the Law of the Sea.

The laws "improve our capacity for governance and reinforce our maritime policies for economic development and for national security," Philippine President Ferdinand Marcos Jr. said at the time.