The Construction of Maho Island Base Changes the Geopolitics of Southwest Defense — The Maneuvering Over the Japan-China Strait and the Self-Defense Forces' AI Transformation

On Mageshima, part of the Osumi Islands in Kagoshima Prefecture, large-scale military facility construction is progressing day and night. This small uninhabited island, measuring approximately 4.5 kilometers north to south and 2.7 kilometers east to west, is set to be transformed into "a base for the Self-Defense Forces covering the entire island," an unprecedented form. The project, which began construction in 2023, aims for completion by 2030, and if completed, it will fundamentally change Japan's southwestern defense posture.

As confirmed from the plans and press photos released by the Ministry of Defense, Mageshima will have two runways: a main runway measuring 2,450 meters and a crosswind runway measuring 1,830 meters. With two runways oriented in different directions, aircraft will be able to take off and land regardless of wind direction or weather conditions. Training for the Japan Air Self-Defense Force's latest stealth fighter, the F-35B, is planned to take place here. Furthermore, the simulated takeoff and landing training (FCLP) for U.S. Navy carrier-based aircraft, currently conducted at Iwo Jima (Tokyo), is also expected to be relocated to Mageshima. The distance from the U.S. Navy's Iwakuni base (Yamaguchi Prefecture) to Iwo Jima is about 1,400 kilometers, but this will be shortened to about 400 kilometers with Mageshima, significantly improving training efficiency.

Various piers, large and small, are being constructed along the island's coastline, allowing Japan Maritime Self-Defense Force escort ships to dock. An amphibious area is also being established, along with training facilities for the Japan Ground Self-Defense Force. This will be a composite base that can be integratively utilized by the three branches of the Self-Defense Forces: maritime, air, and land. In the future, it is expected that about 150 to 200 Self-Defense Force personnel will be stationed there, with personnel and their families residing on Tanegashima, approximately 10 kilometers to the east, commuting to Mageshima by ferry.

The strategic value of Mageshima extends beyond being merely a training facility. It plays a central role in the Ministry of Defense's concept of mobile and dispersed operations. In the event of an emergency, air bases become the top priority targets for enemy attacks. If the runway is destroyed, fighter jets that have taken off will lose their refueling and ammunition supply points, rendering operational actions impossible. Mageshima is located at a moderate distance from the Miyako Strait and the Amami Oshima Strait, which China considers crucial for its maritime expansion, and will function as a supply and maintenance base for fighter jets and vessels deployed at the front lines during emergencies. It will serve as an unsinkable aircraft carrier floating on the sea.

In response to Japan's strengthening of its southwestern defense capabilities, China's reaction has been extremely severe. Following the passage of a Japan Maritime Self-Defense Force escort ship through the Taiwan Strait on April 17, the Chinese military immediately conducted military training in the western Pacific. The Chinese side announced that it returned through the waters between Yonaguni Island and Iriomote Island in Okinawa Prefecture, which is likely a countermeasure against the JMSDF's passage through the Taiwan Strait. The maneuvering over the strait between Japan and China can be said to have entered a new phase due to Japan's implementation of a passage through the Taiwan Strait, which it had previously avoided.

The backdrop of this military tension between Japan and China is a structural conflict over maritime control from the East China Sea to the Pacific. Since the nationalization of the Senkaku Islands in 2012, China has normalized the intrusion of its coast guard vessels into Japanese territorial waters and frequently passed naval vessels through the Miyako Strait and Osumi Strait. In response, Japan has successively established garrisons on Ishigaki Island, Miyako Island, Amami Oshima, and Yonaguni Island, filling the defense gaps in the southwestern islands. The construction of the Mageshima base can be positioned as the culmination of this series of defense posture enhancements.

On the other hand, Japan's security policy is not only focused on hardware development but is also rapidly transitioning to new domains. The Liberal Democratic Party's proposal for AI policy, revealed on April 22, titled "AI White Paper 2.0," calls for a shift in the way the Ministry of Defense and the Self-Defense Forces operate from the traditional "network-centric warfare" to "AI and data-centric warfare." Given that the U.S. military and the Israeli military are actively utilizing AI for information analysis and target selection in military operations against Iran, there is a judgment that Japan must also accelerate its response. The proposal seeks to reflect this direction in the three security-related documents that will be revised within the year.

What is noteworthy about this proposal is that it explicitly states the balance between ensuring interoperability with allied nations and maintaining autonomy. While considering the connectivity of command and control systems with advanced software from allied nations, it indicates a direction that balances the deepening of the Japan-U.S. alliance with Japan's strategic independence by ensuring autonomy in core areas such as sensitive data storage and access control. Overall, it presents a realistic approach that advocates for the concept of "open AI sovereignty," avoiding complete dependence on specific countries while incorporating domestic production.

When viewed collectively, these movements indicate that Japan's defense policy is evolving simultaneously along two axes: the expansion of physical infrastructure and innovation in the digital domain. By the time the Mageshima base is completed in 2030, a new form of the Self-Defense Forces, based on integrated operations with AI, should also be materializing. The military maneuvering between Japan and China in the southwestern islands will intensify in both physical and information spaces.

However, concerns remain. The accidental detonation of a shell from a Type 10 tank at the Ground Self-Defense Force's Hibiki Training Area in Oita Prefecture on April 21 resulted in a tragic incident, causing the deaths of three personnel and serious injury to one. This unprecedented accident, where the Chief of Staff of the Ground Self-Defense Force, Masayoshi Arai, stated he had no memory of ammunition exploding inside the turret, raises fundamental questions about equipment reliability and the safety of personnel, which could impact the overall defense capability development. Minister of Defense Shinjiro Koizumi promised thorough safety management, but in an era of a 9 trillion yen defense budget, there is also a need to reassess the quality of infrastructure development in light of the harsh realities of official residences and a personnel shortage of 27,000.

The geopolitical transformation of southwestern defense is symbolized by the island of Mageshima. However, the key to its success lies not in the length of the runway or the number of escort ships, but in securing personnel, accurately introducing new technologies, and the maturity of the organization to turn accidents into lessons. As we move toward 2030, Japan's defense will face a series of trials.