Japan Launches Seventh Taigei-Class Submarine Shogei: How Capable Is the Lithium-Ion Boat?

South Korea’s newest boat is bigger and carries more weapons. Hanwha Ocean launched Jang Yeong-sil, the first KSS-III Batch II, at Geoje on October 22, 2025: about 3,500 tons surfaced, roughly 89 meters long, lithium-ion batteries with a fuel-cell auxiliary AIP, and ten vertical launch cells for cruise or ballistic missiles, The War Zone reported. Shogei has no vertical cells. Its missile is the UGM-84L Harpoon Block II, with a reported range of 248 km, fired from its six 533 mm torpedo tubes, Naval News noted. The third Batch II boat was contracted for 1.1 trillion won, about $845 million, the Korea JoongAng Daily reported, against Shogei’s $509 million.

China fields more hulls, though its conventional building has slowed. The PLA Navy operates 13 Type 039 and 21 Type 039A/B Yuan boats plus a small, undetermined number of the newer Type 039C, Naval News counted in January. The War Zone assessed the 039C at roughly 3,600 tons. Hudson Institute analyst Bryan Clark told Stars and Stripes the Yuans are “very quiet” and their AIP gives “a few weeks of submerged endurance”. Japan publishes no endurance figure for its lithium-ion boats, so the quieting contest cannot be settled from open sources.

The Taigei class is Japan’s current diesel-electric attack submarine, built alternately by Mitsubishi and Kawasaki at Kobe since 2018. Each boat is 84 meters long and 9.1 meters in beam, displaces about 3,000 tons standard and carries about 70 crew. Since the fourth boat, Raigei, two Kawasaki 12V 25/31 diesels give about 6,000 horsepower and a submerged speed of about 20 knots, according to Army Recognition. Lithium-ion batteries replaced lead-acid cells and Stirling AIP; Japanese reporting credits them with longer submerged endurance and quieter running, though the Ministry of Defense discloses neither capacity nor endurance. The weapons are six 533 mm tubes for the Type 18 torpedo and the Harpoon Block II. Seven boats have launched, five are in service, and lead boat Taigei became a test submarine in 2024. Ten are planned, the last due in March 2031. They are the newest part of the 22-boat fleet that Japan’s 2023 Defense White Paper describes, up from 16, Asia Times noted.

Shogei’s price sharpens the nuclear question. The Congressional Research Service puts a Virginia-class boat at about $5.0 billion under the fiscal 2026 budget and notes that US yards have managed only 1.1 to 1.2 boats a year since 2022, its January update says. Japan delivers one conventional boat every March for about a tenth of that. Defense Minister Shinjiro Koizumi said on September 11 that the government would “consider all options without ruling anything out”, including nuclear-powered submarines, in the revision of the three security documents due by year-end, and he listed the drawbacks himself: such boats are noisier, costlier, larger and need specialist crews, Naval News reported. The near-term path is conventional. In July the Acquisition, Technology and Logistics Agency gave MHI a ¥3.9 billion contract to design a next-generation boat with vertical launch cells, propulsion undecided.

The chain’s straits, including the Miyako Strait, about 250 kilometers wide by Asia Times’ account, are the passages China’s fleet must use to reach the Pacific. Quiet diesel boats waiting in them are the cheapest way to make that passage costly. China’s estimated 66 submarines, more than half of them conventional, are forecast by the Pentagon to exceed 75 by 2030, Stars and Stripes reported. Japan’s answer is a fleet kept young by one launch a year, and the VLS study is its hedge on missiles, where Seoul and Beijing are ahead.