The Japan Maritime Self-Defense Force’s (JMSDF) sixth Taigei-class diesel-electric attack submarine, JS Sogei, was launched in October 2025 at Kawasaki Heavy Industries’ facilities in Kobe, Hyogo prefecture.
The JMSDF is expanding the roles and missions of its submarine fleet amid rising regional tensions. China is intensifying its military activity in the East China Sea, including around the Japan-controlled Senkaku Islands, and in the Pacific Ocean, according to Japan’s 2025 defense white paper. North Korea is enhancing its weapons of mass destruction and ballistic missile programs, while Russia has conducted naval and aerial activities with China.
The JS Sogei is expected to enter service in March 2027 with a crew of about 70. The $484 million submarine can travel at 20 knots underwater. Sogei means “blue whale” in Japanese.
The new Taigei class has a compact and efficient electricity storage and supply system that extends the submarine’s endurance without increasing its size, according to Japan’s Defense Ministry. Its combat management system combines advanced integrated sensors, command and control, and weapon engagement systems.
An enhanced snorkel system reduces the submarine’s signature and a sonar system based on fiber-optic array technology enhances detection capability. The Taigei class uses Japan’s newest torpedo, the Type 18, which features improvements in propulsion, target detection and processing.
The class also can deploy anti-ship missiles with a range of about 250 kilometers — enough to provide counterattack capability.
The lead submarine of the Taigei class was commissioned in March 2022 and an additional vessel has entered service every subsequent March. The fifth submarine, JS Chogei, launched in October 2024 and is undergoing outfitting and testing for commissioning in March 2026.
