The Japan Maritime Self-Defence Force (JMSDF) commissioned its fifth TAIGEI-class submarine, CHOGEI, into service on 10 March at Mitsubishi Heavy Industries' Kobe Shipyard.

CHOGEI (Long Whale in Japanese) has a length of 84 m, beam of 9.1 m and height of 10.4 m. It has a displacement of 3,000 tonnes and a crew of approximately 70 people. The submarine’s internal design is also optimised to accommodate female crew members.

In a post on X, Japan’s Ministry of Defence called the TAIGEI-class submarines as “Ninjas of the Sea” for their ability to operate stealthily and unnoticed underwater.  The JMSDF commissioned the first of the class ‘TAIGEI’ (“Great Whale” or “Big Whale” in Japanese) into service in March 2022.

The fourth submarine RAIGEI was delivered to the JMSDF in October 2025 by Kawasaki Heavy Industries (KHI). The sixth TAIGEI-class submarine SOUGEI was launched by KHI in October 2025 at its No.1 Building Berth in Kobe Shipyard.

TAIGEI class submarines are equipped with the ZQQ 8 fibre optic array sonar suite and a new integrated combat management system built around the OYX 1 processing system and ZQX 12 tactical display, providing improved detection and engagement capabilities over the earlier SORYU class. The class employs a high strength steel pressure hull, acoustic absorbent coatings, and a floating floor internal structure, along with enhanced snorkel and non penetrating optronic masts, to reduce acoustic and other signatures.

These are also the first in-service submarines globally to have operational lithium-ion battery systems for increased underwater endurance.