Japanese Ministry of Defense
JS Sogei, the sixth Taigei-class submarine of the Japan Maritime Self-Defense Force, was launched in October 2025.
Japan has quietly developed a new type of submarine that is changing the rules of underwater warfare. Your trump card? An innovative lithium-ion battery system, the first of its kind, allows it to stay submerged for several days longer than any traditional model.
In mid-October, in the Kobe shipyards, Japan launched the Sogeia 3,000-ton Taigei-class attack submarine. At first glance, it may look like a conventional diesel-electric hybrid vessel, but it is far from common.
Instead of traditional lead-acid batteries, it uses lithium ion cellswhich offer three to five times greater energy density. The result: a underwater autonomy much longer and a significantly reduced dependence on diesel engines.
Conventional submarines usually use an Air Independent Propulsion (AIP) system, which allows them to recharge their batteries without needing to surface. But these systems present two problems: drastically limit both speed and power.
A Taigei class completely eliminates this restrictionbased solely on energy storage in lithium-ion batteries, which makes the new Japanese submarine almost as versatile as a nuclear powered one., explains to .
But your mission is different. Operating mainly in the vicinity of the Japanese islands, often under tight aerial and naval surveillance of Chinathe determining factor It’s the silence, not the unlimited reach.
These submarines can browse discreetly underwater for up to 12 days at low speed, in contrast to the 3 to 5 days provided by conventional diesel-electric models.
At full power, the lithium-ion system allows the Sogei to reach speeds of 20 knots when submerged — impressive for a non-nuclear ship. The other side of the coin, of course, is ashorter autonomy at higher speeds.
The benefits of this design are both tactical and economic. If there is no nuclear reactor, there is less maintenance requirements and fewer security restrictions, while maintaining broad operational capacity.
However, integrating lithium-ion batteries into submarines it was not an easy task. The Japanese navy it took more than a decade to perfect a safe architecture, as overheating or combustion on board could be catastrophic — there is no way to ventilate or evacuate.
Other navies continue to consider the risk too highbut Japan has already think about the future. Japanese engineers are now working on a new generation of solid-state batteries, which are scheduled to be launched around 2030, in which a solid electrolyte replaces the traditional liquid.
These batteries will be lighter, more efficient and operate at lower temperatures, potentially eliminating the need for complex cooling systems, meaning more space for weapons and electronicsand performance increasingly close to nuclear submarines — all without resorting to a reactor.
For now, the project remains in progress investigation phasebut Japan’s silent revolution underwater may soon redefine the balance of naval power.
