Japan has launched the sixth vessel in its advanced Taigei-class submarine program as it continues to modernize its undersea warfare capabilities amid intensifying maritime competition in the Indo-Pacific region. The launch underscores Tokyo’s commitment to bolstering deterrence and surveillance in strategically contested waters.
Sixth Taigei-Class Submarine Launched by Kawasaki
The latest submarine—reportedly named JS Shōryū (SS-518)—was launched by Kawasaki Heavy Industries (KHI) at its Kobe shipyard on October 10, 2025. This marks the third Taigei-class boat constructed by KHI; the other three have been built by Mitsubishi Heavy Industries (MHI). The vessel is expected to be commissioned into service with the Japan Maritime Self-Defense Force (JMSDF) in March 2027 following outfitting and sea trials.
The launch ceremony was attended by senior officials from Japan’s Ministry of Defense and KHI executives. The event comes as Tokyo accelerates procurement and deployment of high-end naval assets to counter growing Chinese naval activity around the Senkaku Islands and in the broader East China Sea.
Taigei-Class Overview: Advanced Diesel-Electric Design
The Taigei-class (meaning “Big Whale”) is Japan’s newest generation of diesel-electric attack submarines (SSKs), succeeding the Sōryū-class. It retains a similar hull form but introduces several key technological upgrades:
- Lithium-Ion Battery System: Unlike most conventional submarines that rely on lead-acid batteries or Air Independent Propulsion (AIP), the Taigei class uses a high-capacity lithium-ion battery system developed domestically by GS Yuasa. This allows for longer submerged endurance and faster charging cycles compared to AIP-equipped boats.
- Displacement: Approximately 3,000 tonnes submerged—slightly larger than Sōryū-class units.
- Propulsion: Diesel-electric propulsion with a single screw driven by an electric motor; no AIP module is installed due to reliance on advanced batteries.
- Sensors & Combat Suite: Equipped with a new sonar suite likely derived from earlier OYQ-11 systems; includes flank arrays and improved acoustic processing for littoral operations.
- Crew Comfort & Automation: Enhanced habitability and increased automation reduce crew workload while improving operational sustainability.
The class is designed for stealthy patrols in shallow waters near archipelagic zones—ideal for monitoring choke points such as the Miyako Strait or Bashi Channel.
Fleet Expansion Plan: Up to Seven Units Confirmed
The Japanese Ministry of Defense plans to build at least seven Taigei-class submarines under its current Mid-Term Defense Program (MTDP). As of late 2025:
- JS Taigei (SS-513): Commissioned March 2022
- JS Hakugei (SS-514): Commissioned March 2023
- JS Jingei (SS-515): Commissioned March 2024
- An unnamed fourth unit (SS-516): Undergoing sea trials
- An unnamed fifth unit (SS-517): Fitting out phase
- JS Shōryū (SS-518): Launched October 2025
The seventh unit has been funded under Japan’s FY2024 defense budget. Given ongoing regional tensions, analysts expect further orders beyond these seven as part of Japan’s long-term goal to maintain a fleet of at least 22 operational submarines—a number already met but now being modernized with newer platforms.
Lithium-Ion Batteries: Strategic Edge or Risk?
The most distinctive feature of the Taigei class remains its use of lithium-ion batteries—a global first when introduced aboard late-model Sōryū boats SS-511 Ōryū and SS-512 Tōryū. These batteries offer several advantages over traditional AIP systems:
- No need for liquid oxygen or fuel cells simplifies logistics and reduces noise signature.
- Sustained higher speeds underwater without surfacing or snorkeling for extended periods.
- Lighter weight and more compact footprint allow additional space for sensors or crew comfort improvements.
However, lithium-ion technology also carries risks—primarily related to thermal runaway events if not properly managed. To mitigate this, Japanese engineers have implemented multiple layers of safety controls including battery management systems, fire suppression modules, and redundant cooling architectures. So far, no major incidents have been reported across four operational boats using this technology since their introduction in early 2020s.
Tactical Role in Indo-Pacific Maritime Strategy
The expansion of Japan’s undersea fleet comes amid growing concerns over Chinese naval assertiveness across key maritime routes. The East China Sea has seen increased PLA Navy presence near disputed territories such as the Senkaku/Diaoyu Islands. In response, JMSDF has intensified ISR patrols using both manned submarines and P-1 maritime patrol aircraft supported by US Navy cooperation under bilateral agreements like the U.S.-Japan Defense Guidelines.
The stealthy nature of diesel-electric subs makes them ideal for area denial missions within Japan’s Exclusive Economic Zone (EEZ) and first-island-chain chokepoints. The Taigei class enhances these capabilities through improved acoustic stealth and longer submerged loiter times—critical factors when tracking adversary movements or deploying special forces teams covertly during crisis scenarios.
Kawasaki vs Mitsubishi: Dual Build Strategy Maintains Industrial Base
The decision to split construction between Kawasaki Heavy Industries and Mitsubishi Heavy Industries reflects Japan’s longstanding policy of sustaining parallel shipbuilding capabilities across major defense contractors. This dual-source strategy ensures resilience against supply chain disruptions while maintaining competitive innovation between firms specializing in naval systems integration.
Kawasaki builds its submarines at Kobe Works; MHI operates from its Kobe Shipyard & Machinery Works as well as Kure Shipyard depending on project loadouts. Both companies collaborate closely with MoD’s Acquisition, Technology & Logistics Agency (ATLA) on design evolution based on user feedback from deployed units—particularly regarding acoustic performance optimization against evolving Chinese ASW threats such as Type-056 corvettes or Y-8Q aircraft equipped with MAD sensors.
Outlook: More Submarines Likely Amid Regional Arms Race
The launch of JS Shōryū signals continued investment in high-end conventional submarine capabilities—a trend mirrored by other regional actors including Australia’s SSN-AUKUS program and South Korea’s KSS-III Batch II boats featuring VLS cells for cruise missiles. While Japan remains constitutionally constrained from offensive power projection, its emphasis on sea denial platforms aligns with defensive doctrine focused on homeland protection through layered deterrence strategies.
If current trends persist—including record defense budgets exceeding ¥7 trillion ($47 billion USD) annually—the JMSDF could eventually expand beyond its current force structure cap via reinterpretation of Article IX constraints or through enhanced joint operations with Quad partners focused on Indo-Pacific security architecture resilience against coercive behavior at sea.
