Japan launches 7th Taigei-class submarine JS Shogei with lithium-ion batteries for longer underwater operations.

Mitsubishi Heavy Industries launched the JS Shogei (SS-519) at its Kobe shipyard on October 8, 2026, marking the seventh Taigei-class diesel-electric attack submarine constructed for the Japan Maritime Self-Defense Force. Built at a cost of ¥80.5 billion, the 3,000-tonne vessel integrates advanced lithium-ion battery propulsion, floating machinery mounts, and the ZQQ-8 sonar suite to reduce acoustic signatures. Following outfitting and sea trials, the submarine is scheduled for formal delivery in March 2028 to bolster regional underwater patrol capabilities.

The JS Shogei measures 84 meters in length with a 9.1-meter beam and a hull depth of 10.4 meters, operated by a complement of 70 crew members. Its propulsion system combines two Kawasaki 12V 25/31 diesel generators and high-capacity lithium-ion storage, while its armament configuration utilizes six 533 mm bow tubes capable of deploying Type 18 heavyweight torpedoes and UGM-84L Harpoon Block II anti-ship missiles.

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The JS Shogei's lithium-ion batteries allow it to remain submerged longer, operate at higher speeds on battery power, and recharge faster, reducing both the time spent snorkeling and its exposure to enemy detection. (Picture source: MHI)

On October 8, 2026, Mitsubishi Heavy Industries (MHI) launched the JS Shogei (SS-519), the seventh Taigei-class diesel-electric attack submarine (SSK), at its Kobe shipyard in Hyogo Prefecture, Japan, ahead of delivery to the Japan Maritime Self-Defense Force (JMSDF) in March 2028. Laid down on April 17, 2024, the submarine, whose construction costed ¥80.5 billion ($509 million), measures 84 meters in length, 9.1 meters in beam and 10.4 meters in hull depth, with a standard displacement of 3,000 tonnes and a crew of 70. Its propulsion combines two Kawasaki 12V 25/31 diesel engines, lithium-ion batteries and a single propeller shaft, while six 533 mm torpedo tubes accommodate Type 18 heavyweight torpedoes and UGM-84L Harpoon Block II missiles.

The launch, attended by 300 participants, marked the launch of the fourth Taigei-class submarine built by Mitsubishi and the 32nd submarine constructed at MHI's Kobe facility since World War II. The JS Shogei will now undergo outfitting and testing before delivery, as Japan also studies a ¥3.9 billion ($24.6 million) next-generation submarine project potentially involving vertical launching systems (VLS) and considers whether nuclear propulsion could meet future operational requirements. The Taigei-class follows three decades of Japanese submarine development in which hull dimensions have changed relatively little while simultaneously transitioning from lead-acid batteries and air-independent propulsion toward larger lithium-ion energy reserves. The Oyashio-class, introduced in 1998, displaced 2,750 tonnes, measured 82 meters by 8.9 meters, and used diesel-electric propulsion with lead-acid batteries.

Its successor, the Soryu-class, introduced in 2009, increased the standard displacement to 2,900 tonnes, the length to 84 m, and the beam to 9.1 meters, with its first ten vessels incorporating four Stirling air-independent propulsion (AIP) engines for low-speed underwater operation without snorkeling. The final two Soryu submarines, Oryu (SS-511) and Toryu (SS-512), abandoned this AIP system in favor of lithium-ion storage. The Taigei-class further increased the standard displacement to 3,000 tonnes by incorporating lithium-ion batteries from the initial design stage without lengthening the hull. The class' propulsion system now combines two diesel generators, one electric motor, and a single shaft, for an output of 4,413 kW (6,000 metric horsepower).

The first three vessels retained Kawasaki's 25/25SB engines, before the JS Raigei (SS-516) introduced the 12V 25/31 configuration in 2023, also fitted to the latter JS Chogei (SS-517), JS Sogei (SS-518) and JS Shogei (SS-519). Japan began research on submarine lithium-ion batteries in fiscal 1997 and introduced the technology operationally aboard the JS Oryu in March 2020. Unlike the first ten Soryu submarines, which used Stirling AIP to generate electricity underwater, the Taigei-class relies on stored battery energy when submerged and diesel generators when snorkeling. Lithium-ion batteries accept higher charging currents and provide greater usable energy density than lead-acid batteries, leading Japan to develop higher-output diesel engines, increased intake and exhaust capacity, and several modifications to reduce detection while the submarine recharges.

The Taigei-class's reported submerged speed reaches 20 knots (37 km/h), equivalent to 200 nautical miles in ten hours if sufficient energy is available. Actual battery capacity in MWh, charging duration and endurance at 5, 10 or 20 knots remain undisclosed, preventing a quantified comparison with AIP-equipped Soryu submarines or nuclear-powered vessels. The JS Shogei also incorporates changes intended to reduce the transmission of machinery noise into seawater while improving passive acoustic detection through the ZQQ-8 integrated sonar suite, two requirements that become increasingly important when tracking submarines operating at low speeds. Japan developed floating machinery mounts between 2007 and 2014, allocating ¥400 million to reduce vibration and improve resistance to external shock, at the expense of internal volume.

The ZQQ-8 combines bow-mounted sonar, flank arrays and a fiber-optic towed array, allowing acoustic reception from different positions and reducing interference from the submarine's machinery. Research included conformal bow receivers, flank hydrophones integrated with sound-absorbing materials, directional compensation for towed arrays and automatic contact correlation. The OYX-1 processing subsystem combines these acoustic inputs, while the ZQX-12 tactical display supports contact classification, tracking and weapon employment. Additional equipment includes the NZLR-2 electronic support system for detecting electromagnetic emissions, the ZPS-6H navigation radar, and non-hull-penetrating optronic masts, which transmit imagery electronically rather than requiring a conventional optical tube through the pressure hull. The JS Shogei retains the six 533 mm bow-mounted torpedo tubes used by earlier Japanese attack submarines, capable of firing Type 18 heavyweight torpedoes and encapsulated UGM-84L Harpoon Block II anti-ship missiles.

The Type 18 heavyweight torpedo replaces the Type 89 and incorporates changes to propulsion, target-detection equipment, and onboard signal processing. For its part, the UGM-84L has a reported range of 248 kilometers (134 nautical miles), and requires target-location information beyond the submarine's immediate sensor coverage for long-range engagements. In May 2015, the U.S. State Department approved a possible $199 million sale of 48 UGM-84L missiles to Japan, including containers, spare parts, training and support, equivalent to $4.15 million per missile when all package costs are included. The Taigei-class also carries torpedo countermeasures derived from equipment introduced aboard the final four Soryu-class submarines, providing more defensive options against incoming torpedoes. Japan's two submarine builders have also alternated the Taigei-class launches annually since 2020.

Mitsubishi Heavy Industries (MHI) launched the JS Taigei (SS-513) in October 2020, the JS Jingei (SS-515) in October 2022, the JS Chogei (SS-517) in October 2024 and the JS Shogei (SS-519) in October 2026, while Kawasaki Heavy Industries (KHI) launched the JS Hakugei (SS-514) in October 2021, the JS Raigei (SS-516) in October 2023 and the JS Sogei (SS-518) in October 2025. The first five submarines entered service between March 9, 2022, and March 10, 2026, with the JS Sogei scheduled for March 2027 and the JS Shogei for March 2028. The lead submarine, the JS Taigei, was reassigned as experimental submarine SSE-6201 in March 2024, allowing the JMSDF to evaluate new equipment without repeatedly withdrawing operational submarines from patrol assignments. The JS Shogei's ¥80.5 billion cost exceeds the lead vessel's reported ¥80 billion by ¥500 million, or 0.625% in nominal terms.

Production is already continuing with SS-520, laid down on December 19, 2024, and SS-521, laid down on April 15, 2026, which are scheduled for delivery in March 2029 and March 2030. Japan's next submarine program addresses a different requirement by focusing on incorporating long-range missiles into dedicated vertical launch cells (VLS) rather than relying exclusively on the six forward torpedo tubes. The National Security Strategy, National Defense Strategy and Defense Buildup Program adopted in December 2022 established the policy basis for acquiring longer-range stand-off strike capabilities, including weapons intended to engage targets beyond the immediate vicinity of Japanese forces. Consequently, on July 6, 2026, the Acquisition, Technology & Logistics Agency (ATLA) awarded MHI a ¥3.9 billion ($24.6 million) contract for the overall ship-design optimization of a next-generation submarine equipped with vertical launching systems.

Kawasaki Heavy Industries has separately received an order in 2023 for research linked to submarines capable of employing stand-off missiles and has examined future underwater propulsion technologies, including carbon dioxide separation and capture concepts. As of October 8, 2026, Japan has not finalized the next-generation submarine's displacement, VLS cell count, missile selection, propulsion configuration, construction budget, or commissioning schedule. The propulsion question is particularly important for Japan because its submarines may need to operate across distances extending from the Japanese home islands to the East China Sea, Philippine Sea, and wider Western Pacific, where transit time and exposure during battery recharging affect deployment planning.

Therefore, nuclear propulsion remains under consideration because a larger VLS-equipped submarine could require greater electrical power and sustained submerged speed than Japan's existing diesel-electric vessels. A September 2025 advisory panel recommended the further development of next-generation propulsion, and Defense Minister Shinjiro Koizumi confirmed on September 11, 2026, that nuclear-powered submarines would not be excluded from consideration. The operational difference can be illustrated through sustained transit speed: a submarine maintaining 20 knots covers 480 nautical miles (889 kilometers) in 24 hours, and 2,400 nautical miles (4,445 kilometers) in five days. A nuclear-powered submarine can sustain high submerged speeds without periodically operating diesel generators, whereas a Taigei-class submarine must manage its battery reserves and return to snorkeling depth when recharging becomes necessary.

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Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, South Korea, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.