Japan's 'Big Whale' submarines add another weapon to bottle up China's navy

• Japan has launched a new Taigei-class sub every year since 2020.
• These "Big Whale" subs are expected to hunt Chinese warships should a war break out.

In October, Kawasaki Heavy Industries launched Japan’s newest submarine in a ceremony at its shipyard in Kobe, Japan. Named, JS Raigei (“Thunder Whale” in Japanese), the diesel-electric attack sub is the fourth boat of the Taigei-class, which translates to “big whale.”

Its launch comes almost exactly one year after the launch of the third Taigei-class sub, JS Jingei (or “Swift Whale”). With a building time of about two years each, Japan has launched a new Taigei-class sub every year since 2020.

The quick timetable demonstrates more than the excellent turnaround time of Japan’s major shipbuilders; it also demonstrates Japan’s resolve to modernize its submarine fleet with a new class of diesel-electric submarine regarded as one of the best anywhere in the world.

Featuring a host of new technologies and innovations, Taigei-class subs were designed in large part to defend from the very real and growing threat posed by China’s navy, and are expected to play an essential role in hunting Chinese warships should a war break out.

New threats, advanced subs

Japan’s submarine prowess is the result of a large industrial base and a wealth of experience building and operating submarines for over a century.

Japan’s Sōryū-class, pronounced “soar-yuu,” has been especially lauded for its effectiveness and advanced capabilities, including being one of the first frontline submarine classes to be equipped with air-independent propulsion (AIP) technology, which allows diesel-electric boats to operate underwater for longer periods.

The technological sophistication of their submarines, combined with the might of allied US Navy nuclear-powered attack subs, enabled Japan’s navy, known officially as the Japan Maritime Self-Defense Force (JMSDF), to field a small sub fleet compared to its neighbors.

Even in the years immediately after the Cold War, with the threat from the Soviet Union virtually vanishing overnight and the one from Russia appearing significantly degraded compared to its forebear, China’s submarine fleet, though large, was still mostly regarded as generations behind in terms of capability, resulting in a technological gap.

In recent years, however, that gap has closed dramatically.

China’s current sub fleet, numbering some 59 boats, includes approximately 10 improved Kilo-class, 12 Type 039-class, and 21 Type 039A-class diesel-electric attack subs. The force also includes six Type 093/093A nuclear-propelled attack submarines and six Type-094 nuclear-powered ballistic missile submarines.

Those models are equipped with modern systems and weaponry, and have modern capabilities. The Yuan-class boats, for instance, are outfitted with AIP technology, and appear to be getting upgrades to make them stealthier.

What’s more, China has become increasingly assertive with its naval forces, including around the Senkaku Islands, which Beijing claims but Japan maintains sovereignty over.

Consequently, Japan needs to both increase the size of its submarine fleet, and equip each sub with advanced technologies to achieve a qualitative advantage.

The Big Whale

In 2010, a year after the commissioning of the first Sōryū-class sub, Japan unveiled plans to increase its submarine fleet from 16 to 22 boats. It also continued to pursue new technologies it had started researching in the first decade of the 2000s.

One of those technologies was lithium-ion (Li-ion) batteries. Much more efficient than standard lead-acid batteries, Li-ion batteries maintain a larger voltage potential as they discharge energy. They are also generally more energy dense and can be capable of storing twice as much energy as lead-acid batteries.

For submarines, this means faster accelerations and top speeds, more time underwater, less maintenance, faster recharge times, lower noise levels, and better overall performance. Li-ion batteries also negate the need for AIP, since they are more efficient and already store so much energy. Submarines need burst speeds to evade depth charges and homing torpedoes.

While other navies have been reluctant to adopt Li-ion batteries for submarines because of the risks of them malfunctioning and starting fires, Japan became the first (and so far only) country to integrate the technology into submarines with the commissioning of the final two Sōryū-class subs, JS Ōryū, and JS Tōryū.

In 2020, Japan launched JS Taigei, the lead boat of its class and the first submarine designed from the outset to carry Li-ion batteries. Commissioned in 2022, it is similar in appearance to the Sōryū-class, but is slightly larger, measuring 275 ft long and 30 ft wide, with a surface displacement of approximately 3,000 tons. A US Navy Los Angeles class attack sub, by comparison, is about 90 feet longer.

Like the Sōryū-class, it is built with an X-shaped rudder for enhanced propulsion performance and operates the same countermeasure system. It is also equipped with the same ZPS-6F surface/low-level air search radar, carries the same towed array sonar, and has an optronic mast.

But the Taigei-class also has new systems in addition to the Li-ion batteries, including a new snorkel system, a new sonar system based on fiber-optic array technology, a new combat management system that gathers data from all sensors, and a pump-jet propulsor.

With a crew of 70, the Taigei-class is also built with a female-only section in the crew compartment for six female submariners- the first such accommodation in a Japanese submarine.

The subs have six torpedo tubes for Type 89 and Type 18 torpedoes, and are capable of launching UGM-84 Harpoon anti-ship missiles.

A central role

Submarines have long been expected to play a dominant role in a potential future conflict with China, and Japanese subs are viewed as especially important. Wargames simulating a Chinese invasion of Taiwan conducted by the Center for Strategic and International Studies last year even described Japanese submarines as “most valuable.”

Because of their advanced capabilities and stealthy attributes, they would be prime candidates for ambushes on Chinese warships in strategic naval choke points in the East and South China seas, as well as in the Sea of Japan.

Of particular importance are the Miyako Strait and Bashi Channel; the bodies of water between Japan and Taiwan, and Taiwan and the Philippines, respectively.

Japanese subs, as well as submarines from allied and partner nations like the US, UK, and Australia could turn those bodies of water into kill zones, restricting the Chinese navy’s freedom to maneuver and its ability to send ships and submarines to the Second Island Chain and beyond.

The JMSDF conducted anti-submarine warfare drills with one of its submarines in the South China Sea in September and conducted its first joint ASW exercise with the US Navy in the area in 2021.

Being the most modern submarine in its fleet, the Taigei-class would play a central role in these efforts.

Japan has so far launched four Taigei-class submarines since 2018; JS Taigei, JS Hakugei, JS Jingei, and JS Raigei. Only the first two have been commissioned into service, though JS Jingei is expected to be commissioned in March. JS Raigei is planned to be commissioned in 2025.

Japan plans to acquire at least seven Taigei boats. They will replace the JMSDF’s Oyashio-class subs, the first of which was decommissioned last year.