Japan commissions fourth Taigei-class submarine Raigei to enhance surveillance of China’s naval expansion.

On March 6, 2025, the Japan Maritime Self-Defense Force (JMSDF) held a handover and commissioning ceremony for the submarine Raigei at Kawasaki Heavy Industries' Kobe Shipyard. This event marked the official transfer of the fourth Taigei-class submarine to the JMSDF. The ceremony was attended by key officials, including Parliamentary Vice-Minister of Defense Yozo Kaneko, Chief of Staff of the Maritime Self-Defense Force Ryo Saito, and senior officials from the Ministry of Defense and Kawasaki Heavy Industries. During the event, the Self-Defense Forces' flag was presented to the submarine, symbolizing its formal induction into the fleet.
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The Raigei is the first Taigei-class submarine to be equipped with the upgraded Kawasaki 12V 25/31 diesel engines, which provide increased power generation efficiency during snorkeling operations. (Picture source: Twitter/@RyoEto)

The Raigei (or JS Raigei, SS-516) is a 3,000-ton diesel-electric attack submarine designed to enhance Japan's maritime defense capabilities. It measures 84 meters in length, 9.1 meters in width, and 10.4 meters in depth. The vessel is equipped with two Kawasaki 12V 25/31 diesel engines and a single propulsion motor connected to a one-shaft system. It also features advanced lithium-ion batteries, which improve underwater endurance and operational flexibility compared to conventional submarines. The submarine can achieve an underwater speed of approximately 20 knots and has a crew complement of around 70 personnel.

The Raigei's design incorporates enhanced stealth and detection capabilities. It is fitted with the ZQQ-8 sonar suite, an upgrade over the ZQQ-7 system used in the preceding Soryu-class submarines. The vessel also employs a new combat management system that integrates advanced sensor technologies to improve situational awareness. Additionally, the Raigei is the first Taigei-class submarine to be equipped with the upgraded Kawasaki 12V 25/31 diesel engines, which provide increased power generation efficiency during snorkeling operations. The vessel is also capable of accommodating female crew members, with designated sleeping quarters for up to six personnel.

Its armament includes six 533mm HU-606 torpedo tubes capable of launching Type 18 torpedoes and UGM-84L Harpoon Block II anti-ship missiles. These systems provide the submarine with offensive capabilities against both surface and subsurface threats. The Harpoon missile has a range of approximately 248 kilometers, allowing for engagement of targets beyond visual range. The Raigei is also outfitted with electronic warfare and countermeasure systems designed to enhance survivability against enemy detection and attacks.

The submarine was constructed under the JMSDF's Mid-Term Defense Program and follows a structured timeline. Its keel was laid down on March 26, 2021, it was launched on October 17, 2023, and it was officially commissioned on March 6, 2025. This marks the latest addition to Japan's growing fleet of modern submarines, following the commissioning of Taigei in 2022, Hakugei in 2023, and Jingei in 2024. The fifth submarine in the class, Chogei, was launched in October 2024 and is expected to enter service in 2026.

The Raigei has been assigned to the 1st Submarine Squadron of Submarine Flotilla 1, stationed at the Kure Base in Hiroshima Prefecture. It will play a critical role in Japan's maritime security strategy, particularly in response to increasing naval activities in the region. With the Chinese Navy expected to expand its presence in the Western Pacific, Japanese submarines, known for their stealth capabilities, are anticipated to play a key role in monitoring and deterring potential threats.

The Taigei class currently consists of five planned units, such as the Jingei, with four already commissioned and the fifth expected to enter service in 2026. (Picture source: Japan Maritime Self-Defense Force)

The Taigei-class submarines were developed as a successor to the Soryu-class, incorporating lessons learned from previous designs while improving stealth, endurance, and detection capabilities. Research and development on the new class began in the early 2000s, with an emphasis on lithium-ion battery technology, which provides longer submerged endurance compared to traditional lead-acid batteries. The hull structure and sonar suite were also modernized to enhance survivability and operational effectiveness in Japan’s regional maritime environment. The class incorporates a new-generation sonar system based on fiber-optic array technology, as well as a redesigned snorkel system that improves power generation efficiency while reducing detectability. The first unit, JS Taigei, was commissioned in 2022, marking the beginning of a new generation of Japanese submarines.

The class currently consists of five planned units, with four already commissioned and the fifth expected to enter service in 2026. These submarines are assigned to the JMSDF’s Kure and Yokosuka bases, strategically positioned to monitor regional maritime activity. Their improved sonar and anti-detection capabilities allow them to operate effectively in contested waters, reflecting Japan’s broader efforts to enhance its deterrence posture. The Taigei-class represents an evolution in Japan’s submarine doctrine, with a focus on maintaining technological superiority in undersea operations. Additionally, the Raigei is the first unit of the class to be equipped with the new Kawasaki 12V 25/31 diesel engine, a key upgrade that enhances its operational capabilities. The adoption of lithium-ion batteries across the class aligns with Japan's focus on increasing underwater endurance while reducing the acoustic signature of its submarines.

With growing concerns about regional security, the Taigei-class submarines are expected to play an essential role in countering potential maritime threats. Japan remains the only country known to have fitted lithium-ion batteries in its submarines, a technological advancement that enables longer patrol durations and greater operational flexibility. As tensions rise in the Indo-Pacific, these Taigei-class submarines are expected to contribute to Japan’s maritime security strategy by monitoring the Chinese Navy’s expanding presence in the Western Pacific, including increased patrols and aircraft carrier operations. Their enhanced sonar capabilities and extended underwater endurance allow for sustained surveillance of maritime routes and potential naval movements in the region.