Crossing the Nansei Islands Waters by the People's Liberation Army Navy and the Dramatic Changes in the Northeast Asian Maritime Security Environment

In the third week of April 2026, the maritime security environment in East Asia is rapidly escalating in tension. The 133rd Fleet of the People's Liberation Army (PLA) Eastern Theater Command conducted exercises in the western Pacific, passing through international waters around Japan's southwestern islands and returning via the Yonaguni-Iriomote waterway between Iriomote Island and Yonaguni Island. This waterway is located just 110 kilometers from Taiwan, and Yonaguni Island, as Japan's westernmost inhabited island, holds a strategically significant position due to its proximity to Taiwan. This is the first time that the PLA's surface vessels have been publicly confirmed to have navigated through the Yonaguni-Iriomote waterway.

In a statement on April 22 (Wednesday), the PLA Eastern Theater Command stated, "We organized the 133rd Fleet, completed training exercises in the western Pacific, and returned via the Yonaguni-Iriomote waterway. This effectively verifies the unit's long-range operational capabilities." The fleet chose to pass through the Yokotose Strait in Kagoshima Prefecture on the outbound journey and selected the Yonaguni-Iriomote waterway for the return trip. The choice of these two routes can be interpreted as a deliberate show of force against Japan's defense posture along the southwestern islands. Song Zhongping, a former PLA instructor and military analyst, clearly positioned this navigation as a "warning to Japan." He pointed out, "This rare passage is a direct deterrent to Japan's military bases deployed along the coast."

The backdrop to this movement is a change in Japan's Taiwan-related policy. In recent years, the Japanese government has clearly positioned a potential Taiwan crisis as a significant concern for its national security and has focused on strengthening the defense of the southwestern islands. The Self-Defense Forces have established bases on Yonaguni Island, Ishigaki Island, and Miyako Island, deploying coastal surveillance units and anti-ship missile units. The PLA's recent navigation should be understood as a direct military message against Japan's southwestern shift.

At the same time, tensions were also rising in the South China Sea. On April 24 (Friday), the PLA Southern Theater Command announced that it conducted naval exercises in the waters east of Luzon Island. This exercise was described as a "necessary response to the current regional situation," and a formation of four ships, led by the Type 055 missile destroyer "Zunyi," was confirmed. Satellite images suggest that up to 14 large vessels, including the Liaoning aircraft carrier, may have participated in the exercise. The timing of this exercise coincides with the start of the U.S.-Philippines joint exercise "Balikatan 2026" (April 20), indicating that the strategic competition between the U.S. and China is unfolding simultaneously in both the East and South China Seas.

Balikatan 2026 is a large-scale annual joint exercise lasting 19 days, led by the United States and the Philippines. In recent years, the Balikatan exercises have continued to expand in scale, with approximately 17,000 troops participating in the 2024 exercise. The PLA Southern Theater's conduct of exercises in the waters east of Luzon during this period clearly has the character of a countermeasure against the U.S.-Philippines alliance.

Furthermore, noteworthy is an editorial on artificial intelligence (AI) published by the People's Liberation Army Daily on April 24. The paper analyzed the use of AI in the Iran War and evaluated that "this is the first time AI technology has been integrated into all stages of operations." Specifically, it pointed out that AI is incorporated into the entire cycle from information analysis to target identification, operational planning, and effectiveness evaluation, positioning AI as the "core engine for reconstructing the forms of warfare, military structures, and the global strategic framework." This editorial clearly indicates the PLA's policy of rapidly promoting the military application of AI, which could have significant implications for the security environment in Northeast Asia.

The United States is not remaining passive either. This week, U.S. Navy Colonel Garrett Miller revealed plans to deploy more than 30 medium unmanned surface vessels in the Indo-Pacific by 2030, along with thousands of small drone boats and aerial systems. This is a realization of the "Healthscape" concept proposed by U.S. Indo-Pacific Command General Samuel Paparo. While Taiwanese defense analysts generally welcome this plan, they point out that Taiwan's own drone fleet concept is stagnating, indicating that, considering geographical conditions and production capabilities, there are limits to how much capability can actually be demonstrated around Taiwan.

For Japan, this series of events is prompting a re-examination of its defense policy. The Self-Defense Forces continue to strengthen their defense posture in the southwestern islands, but with the PLA's patterns of behavior diversifying and becoming bolder, there is a need to reassess the effectiveness of existing surveillance and alert systems. In particular, the use of new routes like the Yonaguni-Iriomote waterway suggests the potential for scenarios that exceed the assumptions in Japan's defense planning.

These military movements in April 2026 indicate that the balance of power in Northeast Asia is structurally changing. The simultaneous progression of four trends—China's naval power expansion, the acceleration of military applications of AI technology, the U.S. unmanned systems strategy, and Japan's southwestern defense enhancement—interact with each other to reshape the regional security environment. In the coming months, developments in the Taiwan Strait, the southwestern islands, and the South China Sea will likely be key to determining the stability of Northeast Asia.