Japan’s New Taigei-Class ‘Big Whale’ Submarines Have Just 1 Mission

Japan’s Taigei-class (or Big Whale) of diesel-electric attack submarines under construction for the Japan Maritime Self-Defense Force (JMSDF) are categorized as “conventional”—as in being equipped with a non-nuclear-powered propulsion system.

But that is the only aspect of its design that deserves that (sometimes considered denigrating) label. It is anything but conventional in more than one respect.

These submarines have just one mission: Defeat China or North Korea in undersea combat. 

Taigei-Class: A Truly Powerhouse Submarine for Japan 

One is that despite this submarine being the first of its kind to be designed with—and equipped with—several systems based on new-generation technologies, it has been built and launched one after the other, more or less on time.

The fifth submarine in this class was launched only this past October 2024. This is a feat of not falling behind schedule that very few modern and advanced naval platforms can lay claim to.

Moreover, this is a submarine program that has introduced new major subsystems innovations into its design midway through the production line—again without disrupting the construction timeline.

The first Taigei-class submarines and up to the third boat, the Jingei, were powered by two Kawasaki 12V 25/25SB diesel power plants as the main engines. However, the next boat in the series, the Raigei, began using newer-model Kawasaki 12V 25/31 diesel engines with a higher output power level.

The newer diesel engines are also compatible with a re-designed snorkel system that allows for increases in power generation efficiency. According to reports by Japanese defense writers, It is not yet verified that the new engines will increase shaft output for the Taigei-class, currently at 6,000 horsepower, as well as boost the underwater maximum speed to 20 knots.

Taigei-Class Secret Weapon: Batteries and Noise Reduction

The “secret weapon” in the design of these new boats is the use of lithium-ion batteries rather than the lead-acid type historically used in non-nuclear submarines. Japan is, so far, the only nation that has utilized this new technology in submarine design.

These batteries provide the Japan Maritime Self-Defense Force (JMSDF) boats with some of the most advanced underwater performance numbers of any submarine force in the world.

The lithium-ion battery advantages include increased battery discharge rates, faster recharge times, and higher energy density, the latter of which is always the primary objective of any submarine power plant. Lead acid batteries are also less efficient at energy storage than the lithium-ion batteries used in the Taigei subs.

These more advanced batteries recharge at nearly 100 percent efficiency, compared to a maximum 85 percent efficiency rating for most lead acid batteries.

Better battery performance and increased charging efficiency has a number of benefits beyond the batteries themselves just lasting longer.

The improved performance results are:

-Enhanced silent operations

-Better speeds and sprints

-Longer underwater endurance

-Significantly greater overall performance in comparison with other conventional undersea submarines.

However, perhaps the most important difference from the standpoint of the submarine designer is that lithium-ion performance saves weight and complexity by making an air-independent propulsion (AIP) system unnecessary in order to extend the endurance of underwater runs.

Maturing Technology

Lithium-ion batteries have been around for decades. For anyone who has owned a mobile phone since the 1990s, the many superior features of this technology over previous-generation, Nickel-Cadmium battery systems hardly need explaining.

The reason for a three-decade or more gap between the first Nokia model with this class of battery and the use of the lithium-ion technology in a submarine was due to the dangers inherent from the hydrogen gas and intense heat that are produced by these batteries in the event of malfunction and fire. Hence, the announcements onboard most commercial airline flights about not moving your seat and pressing the button to summon cabin crew if your smartphone slips down to the inside of your seat.

The JMSDF and the defense firms it contracted with to develop and mature this technology have somehow managed these potential hazards by engaging in some very extensive research, design, and testing programs.

This process has been in work for more than 20 years and has been developed for aerospace applications as well as marine platforms.

Two submarines of the older Sōryū class that proceeded, the Taigei subs, the Ōryū and Tōryū, were also commissioned with lithium-ion batteries on board. This aided the process of perfecting this technology, matured it to the next level, and made its introduction into the Taigei class possible.

The first of the Taigei-class was built at the Mitsubishi Heavy Industries shipyard in Kobe and commissioned on 9 March 2022.  Its sister ship, the Hakugei, was launched on 14 October 2021 by Kawasaki Heavy Industries in Kobe. The third boat, Jingei, was launched in October 2024 for delivery by early 2024.

The use of both of the Japanese “HI” corporate conglomerates’ shipyards is an important factor in these subs maintaining their production timetable as at least nine Taigei-class submarines are planned for service in the years ahead.

About the Author

Reuben F. Johnson is a survivor of the February 2022 Russian invasion of Ukraine and is now an Expert on Foreign Military Affairs with the Fundacja im. Kazimierza Pułaskiego in Warsaw.  He has been a consultant to the Pentagon, several NATO governments and the Australian government in the fields of defense technology and weapon systems design.  Over the past 30 years he has resided in and reported from Russia, Ukraine, Poland, Brazil, the People’s Republic of China and Australia.