Japan launches sixth Taigei-class submarine JS Sogei amid Indo-Pacific tensions.

Japan has launched its sixth Taigei-class attack submarine, JS Sogei (SS-518), at Kawasaki Heavy Industries’ Kobe Works. The lithium-ion-powered boat strengthens Tokyo’s undersea reach and signals a continued modernization of the Japan Maritime Self-Defense Force.

The Japan Maritime Self-Defense Force announced on its official X account, completed by Kawasaki Heavy Industries, on October 14, 2025, that the sixth Taigei-class attack submarine was named and launched at KHI’s Kobe Works as JS Sogei, hull number SS-518. The 3,000-ton, 84-meter boat carries a crew of about 70 and fields six 533 mm tubes for heavyweight torpedoes and tube-launched anti-ship missiles. Like its sisters, Sogei is built around lithium-ion battery propulsion that prioritizes endurance, sprint performance, and acoustic discretion underwater.
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JS Sogei (SS-518), Japan’s newest Taigei-class submarine, features advanced lithium-ion batteries, high-output diesel engines, and the ZQQ-8 sonar suite, giving it greater speed, stealth, and endurance. Armed with Type 18 torpedoes and Harpoon missiles, it enhances Japan’s undersea deterrence and operational reach across the first island chain (Picture source: Japanese Navy).

Sogei follows a rapid production cadence that has put one Taigei into the water almost every year since 2020, with KHI and MHI alternating builds. From boat four onward, the class adopts Kawasaki’s higher-output 12V25/31 diesels and an improved snorkel generation system, trimming recharge time and exposure at periscope depth. These changes, paired with the large lithium-ion battery bank, give Taigei boats greater sustained submerged speed than legacy lead-acid SSKs and reduce the tactical penalty of coming shallow to breathe. Open sources peg the class at around 20 knots submerged and roughly 6,000 hp installed, numbers consistent with a fast and quiet coastal hunter optimized for the first island chain.

Sensors remain the second pillar: Japanese industry sources and recent reporting indicate the class integrates the ZQQ-8 family sonar suite with new processing, alongside towed and flank arrays and low-probability-of-intercept masts. Combined with the latest Type 18 heavyweight torpedo, which is set to replace the Type 89, Sogei brings a more lethal punch against both submarines and surface combatants. The boat retains UGM-84L Harpoon for anti-ship strikes from the tubes, while Tokyo’s standoff roadmap points to future tube-launched long-range cruise missiles that would extend reach ashore and at sea well beyond Harpoon.

Measured against regional rivals, Taigei’s battery-centric design takes a different path from China’s AIP-equipped Yuan class. PLAN Type 039A/B boats trade sprint power for very quiet, low-speed endurance on fuel cells and are believed to fire YJ-18 anti-ship missiles and Yu-6 torpedoes. South Korea’s KSS-III is larger, AIP-capable, and unique among regional conventionals for its vertical launch cells enabling indigenous land-attack missiles. Taiwan’s first Hai Kun class, still in trials, is smaller and focused on sea denial near the island. In that context, Sogei sits between the high-endurance AIP designs and VLS-armed KSS-III, excelling at fast, covert repositioning and ambush in the Ryukyu gaps while retaining credible strike options from its tubes.

The Taigei blueprint favors what Japanese skippers call sprint-drift hunting. Lithium-ion reserves let Sogei move quickly to a datum, then lie quiet on batteries with minimal loads. The higher-output diesels and new snorkel shorten recharge cycles, limiting exposure to radar and ESM while preserving a low acoustic signature. In peacetime, that translates to persistent ISR, trail, and barrier patrols across choke points from Tsushima to Miyako. In crisis, Sogei can conduct anti-submarine and anti-surface ambushes, lay influence mines via the tubes, and, as Japan fields standoff missiles for submarines, deliver covert land-attack from unpredictable axes, complicating any adversary’s campaign plan.

Chinese and Russian naval activity through the East China Sea and the Philippine Sea has intensified, and Tokyo is expanding a frontline SSK fleet now numbering roughly 23 boats while investing in longer-range strike. Each new Taigei increases the JMSDF’s ability to police the straits, deter coercion around the Senkaku Islands, and plug seamlessly into U.S. and Australian undersea networks. Sogei’s launch shows Japan is not merely keeping pace; it is shaping an undersea force tailored to the first island chain, one able to blunt gray-zone pressure and potentially hold adversary forces at risk.