TAIPEI — Japan deployed long-range missiles capable of reaching China to Kumamoto Prefecture in late March under a new defense strategy known as the "southern shield." The deployment is part of a broader build-up of weapons platforms, electronic warfare and air assets across southern Japan and its southwest outlying islands.

Defence Minister Shinjiro Koizumi said: "Japan faces the most severe and complex security environment in the post-war era and must strengthen its deterrence and responsiveness." Since 2019, Beijing has ranked as Japan's top national security threat, above North Korea and Russia.

The strategy focuses on the Nansei, or Ryukyu, Islands, which run from Kyushu to within 100 kilometers of Taiwan and form a natural barrier dividing the East China Sea from the Philippine Sea. The chain is a component of the U.S.-led First Island Chain maritime defense strategy. China claims Taiwan as a province and has pledged to annex it by peace or by force.

Japan's defense budget hit a record $58 billion for fiscal year 2026, with much of the spending directed to the southern shield build-up. The approach incorporates a shift toward acquiring counterstrike capability. In 2022, Japan's national security strategy was expanded to include counterstrike capabilities, which would allow the Japan Self-Defense Forces to hit back if attacked. Japan is due to acquire 400 U.S.-made Tomahawk missiles that can be launched from submarines and naval vessels.

Kazuto Suzuki, director of the Institute of Geoeconomics, said the geographic orientation of Japan's military posture has been remade. "The balance is changing. The defence posture has completely shifted towards the southwest, so the north is much less prioritised," he said.

Kei Koga, an expert in East Asian security and the U.S.-Japan alliance at Nanyang Technological University, linked the changes to shifts in the regional balance of power. "China's rapid military and nuclear expansion has reduced the credibility of the US extended deterrence," he said. Japan has historically fallen under the protection of Washington's nuclear umbrella. Koga also said: "Japan wants to play a more kind of active role to compensate for the relative gains of China."

Over the past decade, the Japanese government has expanded the legal authorities of the Self-Defense Forces, beginning with a 2014 constitutional ruling that found Japan could participate in the collective self-defense of its allies. Japan renounced the use of war to settle international disputes in 1947. Tokyo will release the next phase of its national security strategy later this year, covering 2026 to 2030.