Japan strengthens island defenses with new submarine, multilayered strategy

Felix Kim

With growing concern over a potential invasion of self-governed Taiwan by Chinese Communist Party (CCP) forces, Japan is enhancing the defense of its southwest Nansei Islands, the Japanese territory nearest Taiwan.

Any attack on the island chain, which is protected by robust air defense systems and Japan’s steadfast alliance with the United States, would prompt a formidable and decisive response. Moreover, Japan’s newest submarines, equipped with stealth technology, advanced surveillance systems and, potentially, long-range missiles, would likely defend the archipelago also known as the Ryukyu Islands, according to analysts.

“China has a limited ability to threaten the Ryukyu Islands. Because there is a U.S. military base on Okinawa [the chain’s largest island], there is little likelihood of a Chinese attempt to seize the island through invasion,” Dr. Timothy Heath, a senior international defense researcher at the Rand Corp., told FORUM. Should CCP forces risk an attack, however, Japanese submarines “could help sink any invading warships,” he said.

The Japan Maritime Self-Defense Force launched its fifth Tagei-class submarine, JS Chogei, in October 2024. The vessels, which are Japan’s largest submarines, are powered by lithium-ion batteries and diesel engines. Able to conduct covert reconnaissance and other missions, they likely would be deployed to defend the Nansei Islands, according to Kuniichi Tanida, a senior researcher at Tokyo’s Institute of Future Engineering.

The Tageis, which are known as “sea ninjas,” can deploy mines and torpedoes, Tanida wrote for the Japanese publication Nippon.com. Arming the submarines with Tomahawk cruise missiles would enable long-range precision strikes, he said. That could provide a crucial strategic asset and deterrent and would align with Tokyo’s 2022 decision to equip the Japan Self-Defense Forces with counterstrike capabilities.

Two additional Tagei-class subs are expected to be operational by 2027, joining the 15 Sōryū-class combat submarines in service since 2009.

In the event of an invasion of Taiwan, which Beijing claims as its territory and threatens to annex by force, the main threat to the Nansei Islands would come from the air, according to Heath. “China would probably rely on missile strikes to damage U.S. aircraft and military facilities” there, he said.

Japan’s multilayered defense strategy for the islands includes ballistic missile defense systems such as Aegis-equipped destroyers and Patriot PAC-3 missile batteries, along with F-35 and F-15 fighter jets. Surface-to-air missile systems, including the Type 03 and Type 12, coordinate with radar, early warning systems and airborne assets.

Japanese Defense Minister Gen Nakatani and U.S. Defense Secretary Lloyd Austin discussed island defenses in early October 2024.

“We will continue to work closely together on important initiatives to strengthen the alliance’s deterrence and response capabilities, such as improving the Japan-U.S. command and control framework, and expanding our joint presence in the southwestern region,” Nakatani said after the leaders’ call.

Felix Kim is a FORUM contributor reporting from Seoul, South Korea.