Key Points – Japan is bolstering its undersea capabilities against regional threats from China with its new Taigei-class “Big Whale” diesel-electric attack submarines.
-The fourth boat in the class, JS Raigei (“thunder whale”), was commissioned in March 2025.
-These submarines are a significant advancement over the preceding Soryu-class, most notably for their pioneering use of high-performance lithium-ion batteries instead of lead-acid ones for propulsion and power.
-This, combined with an advanced ZQQ-8 sonar suite and a potent arsenal of torpedoes and Harpoon anti-ship missiles, makes the Taigei-class a quiet and deadly asset for the Japanese Maritime Self-Defense Force.
Taigei-Class: Japanese ‘Big Whale’ Submarines Aim to Defend Against China
Quick. Please tell me the name of at least one Japanese submarine and the number of submarines they have. You likely do not have a clue. We’re here to clear that up for you because the Japanese maritime self-defense force is busier than ever as China bullies Japan’s neighborhood.
Tokyo must also decide if it would intervene in a Chinese amphibious attack against Taiwan. If China has designs on Japan, too, the Japanese will depend on its submarine program to fight back.
What Is the ‘Big Whale?’
A primary asset for the Japanese Navy is the Taigei-Class “Big Whale” submarine. In fact, Japan has already produced the fourth Taigei-class diesel-electric boat, an attack submarine that will be both quiet and deadly as part of the Maritime Self-Defense Force. The JS Raigei is the newest addition to the Taigei-class. This growing fleet has China taking notice as the Middle Kingdom adds new subs to its own fleet to threaten Japan and the US Navy.
The JS Raigei was built by Kawasaki Heavy Industries in Kobe City. It was commissioned in March. The Raigei and Taigei-class subs are 276 feet long, with a small crew of 70 officers and enlisted sailors. These submarines displace about 3,000 tons. These are slightly longer and heavier than the previous Soryu-class attack subs.
Interestingly, the Taigei-class has a crew compartment for female sailors. Six women can deploy on the sub, according to Naval News.
Raigei Is the Latest of the Taigei-class
Raigei means “thunder whale” in Japanese. The Raigei set Japan back about $470 million to produce. Most of the investment came in the form of a quiet diesel-electric power plant, which the Japanese are understandably proud of due to its power and stealth. It provides about 6,000 horsepower with a speed of 20 knots submerged.
The Taigei-class features enhanced target tracking and improved survivability. This tracking ability is referred to as the ZQQ-8, which is significantly more advanced than the sensors on board the earlier Soryu-class. Japan was concerned its sonars were outdated, and the designers and engineers wanted to improve the sensors on the new subs.
The Batteries Enable Better Electrical Performance
More power is supplied through the new lithium-ion batteries in place of lead-acid ones from the Soryu-class. Japan is the first and only country to supply these types of batteries to their diesel-electric attack subs.
Naval News also noted that “The class also employs a new combat management system [CMS] combining advanced integrated sensors, command-and-control, and weapon engagement systems. In addition, it adopts an enhanced snorkel system to reduce signatures, and a new-generation sonar system based on fiber-optic array technology to enhance detection capability,” according to the Japanese Defense Ministry.
The submarines are equipped with six HU-606 21-inch (533mm) torpedo tubes. The weapons fired are the Type 89 or Type 18 torpedoes. The Taigei-class is also fitted with the UGM-84L Harpoon Block II anti-ship missile.
The Taigei Paved the Way for Better Capabilities
The first sub of the class, the Taigei, was a test submarine for the class and played a crucial role in ensuring the new systems functioned properly in the 2010s. The new diesel-electric engines were put through their paces, and the improved batteries were evaluated to high precision.
The Taigei-class shows that the Japanese are getting more serious about their defense industrial base. A group of military hardware producers are showing that the indigenous ship and submarine-building efforts are bearing fruit.
The question will be just how quiet the diesel-electric sub will be. This will demonstrate the advanced capabilities of the power plant and the overall quality of the construction. Strategically, Japan will have to be aware of how much the Chinese submarine force has grown and whether the Taigei-class can be an actual hunter-killer boat.
The Taigei-class Must Prove Its Worth
I’m not quite sold on the Taigei-class. Japan is not known for its expertise in submarine construction. They seem to be behind on the latest technologies. They need a Stirling advanced air-independent propulsion (AIP) system like the Swedish Gotland-class subs employ. This could have been purchased through a technology transfer deal with the Swedes or emulated in some way. This may have been more expensive, but the quieter propulsion system would be worth it.
However, the Japanese are resolute and skilled engineers and designers. They have one of the best ship-building capacities in the world. It’s just that submarines need extra technological care and advanced workmanship. If any country can deliver precision-cast components for undersea warfare, it is Japan. The Japanese are living in a dangerous neighborhood, and these new submarines can protect the homeland, collect intelligence, surveillance, and reconnaissance data, and destroy enemy shipping.
Let’s see how these “whale” subs do in the coming years. Better propulsion would have been nice, and we’ll see how the current system can evade the enemy subs. One thing is sure: the Japanese are aware of how high the stakes are when it comes to protecting their borders, and submarines are some of the best instruments of naval warfare. It just remains to be seen how well the Taigei-class will execute undersea warfare missions.
About the Author: Dr. Brent M. Eastwood
Brent M. Eastwood, PhD is the author of Don’t Turn Your Back On the World: a Conservative Foreign Policy and Humans, Machines, and Data: Future Trends in Warfare plus two other books. Brent was the founder and CEO of a tech firm that predicted world events using artificial intelligence. He served as a legislative fellow for US Senator Tim Scott and advised the senator on defense and foreign policy issues. He has taught at American University, George Washington University, and George Mason University. Brent is a former US Army Infantry officer. He can be followed on X @BMEastwood.
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