The Japan Maritime Self-Defense Force (JMSDF) has officially commissioned its fourth Taigei-class diesel-electric submarine, JS Raigei (SS 515), marking a significant milestone in Japan’s naval modernization efforts. The new submarine was inducted into Submarine Division 1 of Submarine Flotilla 1 and will be home-ported at Kure Naval Base in Hiroshima Prefecture.
The commissioning ceremony, held at Kawasaki Heavy Industries’ (KHI) Kobe City facility, saw the participation of senior JMSDF officials, representatives from Japan’s Ministry of Defense, and executives from KHI. Raigei’s addition to the fleet strengthens Japan’s underwater warfare capabilities at a time of increasing regional maritime tensions.
JS Raigei differs from its predecessors with several key upgrades. Unlike the lead boat JS Taigei (SS 513) and earlier sister submarines JS Hakugei (SS 514) and JS Jingei (SS 516), Raigei is fitted with the latest Kawasaki 12V 25/31 diesel engines. These new-generation engines offer superior performance compared to the existing Kawasaki 25/25SB powerplants.
Another major upgrade is the inclusion of a newly designed snorkel system, which significantly enhances power generation efficiency, a crucial factor for conventional submarines operating over extended durations. The improvements contribute to reduced noise levels and better endurance, both critical attributes in modern submarine warfare.
Additionally, Raigei introduces dedicated berthing facilities for female crew members, reflecting JMSDF’s ongoing efforts to promote gender integration within its submarine force. This modification is expected to become a standard feature in future Japanese submarines.
As with its Taigei-class predecessors, Raigei is equipped with advanced lithium-ion battery technology supplied by Kyoto-based GS Yuasa. These batteries, first introduced in the final two boats of the preceding Soryu-class—JS Oryu (SS 511) and JS Toryu (SS 512)—provide superior underwater endurance and operational flexibility compared to traditional lead-acid batteries.
Japan remains the first and only nation to successfully field operational submarines utilizing lithium-ion technology. This allows for prolonged submersion without reliance on air-breathing propulsion, making Raigei more challenging to detect compared to submarines using conventional diesel-electric systems. The lithium-ion technology also offers faster recharge rates, increasing the boat’s overall availability for operations.
The Taigei-class is outfitted with an advanced combat management system (CMS), integrating sophisticated sensors, command and control (C2) functions, and weapons systems. This includes:
- OYX-1 Processing System – Enhances data fusion and threat analysis capabilities.
- ZQX-12 Submarine Tactical Display System – Provides a high-resolution, real-time overview of the operational environment.
- ZQQ-8 Fibre-Optic Array Sonar System – Improves target detection and tracking capabilities, especially in complex underwater environments.
- NZLR-2 Electronic Support Measures (ESM) System – Enhances electronic surveillance and threat detection.
- ZPS-6H Radar System – Improves situational awareness, particularly for surface threats.
Additionally, the class features a new non-penetrating mast developed by Mitsubishi Electric. This upgrade improves periscope operations by allowing the crew to conduct surveillance and gather intelligence without physically compromising the boat’s pressure hull.
JS Raigei is armed with six HU-606 533mm torpedo tubes, capable of launching a variety of underwater munitions. Notably, the boat will carry the new Type 18 heavyweight torpedo, which is set to replace the in-service Type 89 torpedo. The Type 18 is expected to offer increased range, improved guidance, and greater lethality against enemy submarines and surface vessels.
The Taigei-class is also expected to be capable of deploying submarine-launched cruise missiles (SLCMs) in the future, should Japan move forward with acquiring such capability. The potential introduction of long-range strike weapons would represent a major shift in Japan’s traditionally defensive naval posture.
The commissioning of JS Raigei comes amid growing security challenges in the Indo-Pacific region. Japan’s defense policy, outlined in the National Security Strategy (NSS) and National Defense Strategy (NDS), emphasizes strengthening deterrence and readiness in response to regional tensions.
China’s rapid naval expansion, including its growing fleet of advanced submarines and aircraft carriers, has pushed Japan to accelerate the modernization of its own maritime forces. The Taigei-class, with its state-of-the-art technology and enhanced capabilities, is designed to counter these emerging threats by improving Japan’s anti-submarine warfare (ASW) and deterrence posture.
Additionally, North Korea’s development of submarine-launched ballistic missiles (SLBMs) remains a concern. The JMSDF’s expanded and modernized submarine fleet will play a crucial role in monitoring and countering potential threats from Pyongyang’s undersea operations.
Japan plans to build at least seven Taigei-class submarines to replace aging Soryu-class boats, ensuring that the JMSDF maintains a fleet of 22 submarines. Following JS Raigei, additional boats are under construction and will be delivered in the coming years.
The Taigei-class is expected to serve well into the 2050s, with further refinements likely as technology evolves. Future iterations may incorporate unmanned underwater vehicle (UUV) integration, advanced sensor suites, and additional stealth enhancements.
The commissioning of JS Raigei marks another step forward in Japan’s efforts to maintain a technologically superior and operationally capable submarine force. With its improved propulsion system, cutting-edge combat suite, and enhanced stealth capabilities, the latest Taigei-class submarine is well-positioned to contribute to Japan’s maritime security in the decades ahead.
