Deployment of Maritime Militias in the East China Sea and South China Sea and Security Cooperation among Three Southeast Asian Countries

In March 2026, the maritime security environment in East Asia is reaching a new turning point. The unusual gathering of thousands of Chinese fishing vessels in the East China Sea, the enhanced activities of the China Coast Guard in the South China Sea, and the exploration of maritime security cooperation among Indonesia, the Philippines, and Vietnam indicate that the strategic balance in this region is fundamentally changing.

The series of events confirmed in the East China Sea clearly exceeds the scope of traditional fishing activities. On December 25, 2025, Jason Wang, CEO of ingeniSPACE, a company specializing in satellite tracking systems and vessel automatic identification system (AIS) data analysis, confirmed that approximately 2,000 Chinese fishing vessels formed two parallel inverted L-shaped geometric formations, with each line extending about 400 kilometers. These vessels maintained a close distance of 500 meters from each other and, under weather conditions close to strong winds, held their positions for about 30 hours before suddenly dispersing.

Wang pointed out that "it is extremely rare for straight lines to form in nature," emphasizing the abnormality of this phenomenon. In fact, past gatherings of fishing vessels in the same waters have been at most around 1,000 vessels, and a mobilization of 2,000 vessels is unprecedented. Furthermore, in early January 2026, about 1,000 vessels formed an irregular rectangle, and in the second week of March, about 1,200 vessels formed two parallel lines, again maintaining their formation for over 30 hours.

Gregory Poling, director of the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies (CSIS) based in Washington, stated, "I have never seen so many Chinese fishing vessels gather outside a port," analyzing that this mobilization is a "demonstrative action from a military perspective." Jennifer Parker, a research fellow at the Australian National University's National Security College and a former naval combat officer, also asserted from her experience, "I have sailed around the world, but I have never seen fishermen operating at such close distances and such concentration. They are clearly not fishing."

Many of these vessels are believed to belong to China's "maritime militia." Analysis of AIS data has revealed that the "overwhelming majority" of the vessels gathered in the East China Sea set sail from Zhejiang Province, which is known to have multiple maritime militia bases. The maritime militia consists of fishing vessels trained for military support and has a track record of supporting China's territorial claims by swarming disputed reefs in the South China Sea.

Thomas Shugart, a former U.S. Navy submarine warfare officer and now a senior fellow at the New America Security Center, points out that the ability to mobilize vessels of this scale can only be attributed to "state operations." The People's Liberation Army Navy of China boasts the largest number of vessels in the world, but it lacks the landing craft necessary for an invasion of Taiwan, making the mobilization of civilian vessels central to operational planning. Shugart analyzes, "Without this civilian-military dual-use maritime force, China cannot execute an invasion of Taiwan. With it, it becomes 'probably possible.'"

Meanwhile, the activities of the China Coast Guard (CCG) in the South China Sea are undergoing significant changes. According to a detailed report released by the CSIS Asia Maritime Transparency Initiative on March 13, 2026, the number of days the China Coast Guard was deployed at Scarborough Shoal in 2025 doubled from 516 days in 2024 to 1,099 days, with patrols confirmed for 352 calendar days. The number of patrol days at Sabina Shoal also increased nearly threefold from 139 days to 405 days, and the coverage area has expanded. In April 2025, the China Coast Guard temporarily landed on Sandy Cay, and in October, it used high-pressure water cannons and engaged in confrontational actions against Philippine fishing vessels near Pagasa Island and Sabina Shoal.

At the same time, the deployment of the China Coast Guard in the Philippine waters around Pagasa Island and Second Thomas Shoal, the Malaysian waters around Luconia Shoals, and the Vietnamese waters around Vanguard Bank has decreased. However, the China Coast Guard continues to monitor oil and gas activities around Vanguard Bank, make contact with Vietnamese fishing vessels near the Paracel Islands, and harass drilling rigs and survey vessels in the waters off Sarawak and North Natuna, Indonesia.

In response to this situation, Indonesia, the Philippines, and Vietnam are seeking to establish a new cooperative framework called the "Maritime Security Triangle." This initiative may include coordination of maritime patrols, information sharing, and joint exercises by coast guard or naval forces. The goal is not to form a military alliance but to enhance collective maritime situational awareness and improve response capabilities to maritime incidents.

This initiative draws inspiration from past regional initiatives aimed at addressing piracy and transnational crime in the Sulu Sea and Celebes Sea. A similar framework applicable to the South China Sea could help countries manage maritime incidents more effectively and maintain regional stability.

However, this trilateral cooperation requires complex diplomatic considerations. Southeast Asian countries traditionally prefer comprehensive regional frameworks that emphasize dialogue and consensus. All three countries are active members of the Association of Southeast Asian Nations (ASEAN), which continues negotiations on the Code of Conduct (CoC) in the South China Sea.

Geopolitical tensions in the South China Sea may change as negotiations on the Code of Conduct reach their final stages. Malaysia, which held the ASEAN chair in 2025, accelerated the pace of negotiations with China on the Code of Conduct. Typically, ASEAN and China hold biannual working group meetings to implement the parties' actions in the South China Sea, but in 2025, five meetings were held.

At a meeting held in Malaysia in August 2025, ASEAN and Chinese officials agreed on a schedule for completing negotiations. The Malaysian Foreign Minister announced that negotiations with China had "made significant progress, reaching agreement on about 70% of the content." If the final 30% of negotiations proceed, a clearer framework for crisis management and maritime cooperation will be provided, potentially easing regional geopolitical tensions even as fundamental disputes continue.

In 2025, the balance of naval power in the South China Sea also showed significant changes. The U.S. Navy deployed four aircraft carrier strike groups to the South China Sea during 2025 and participated in exercises with allied navies. Meanwhile, the U.S. Navy's freedom of navigation operations decreased from an average of 5 to 7 times per year from 2017 to 2024 to just 2 times in 2025.

The Royal Australian Navy conducted four regional deployments in the South China Sea in 2025, including three guided-missile destroyers and one frigate, engaging in joint activities with the Philippines, New Zealand, and the U.S. Navy. In August, a British carrier strike group deployed to the South China Sea and conducted multilateral joint operations in the Philippine Sea and South China Sea.

The People's Liberation Army Navy of China also deployed aircraft carriers to the South China Sea, demonstrating its growing military capabilities. In June, the Liaoning and Shandong simultaneously deployed to the South China Sea and the Western Pacific. In September, the Fujian aircraft carrier, equipped with an electromagnetic catapult, conducted final sea trials in the South China Sea and was officially commissioned in November.

For Japan, these deployments have direct security implications. Tensions between Tokyo and Beijing have deepened after Prime Minister Sanae Takichi suggested the possibility of Japan militarily intervening in the event of a Chinese military action against Taiwan.

The large-scale deployment of maritime militia in the East China Sea, the strategic repositioning of the China Coast Guard in the South China Sea, and the exploration of a new cooperative framework by the three Southeast Asian countries indicate that the maritime security environment in this region has entered a fundamental reorganization phase. As China's military capability development progresses steadily with a timeline toward 2027, regional countries, including Japan, are required to seek a balanced multi-layered response strategy.