How Japan's blue dragons revolutionized underwater endurance through lithium-ion technology
In short: The Sōryū-class marked a turning point for the Japan Maritime Self-Defense Force. By moving beyond traditional lead-acid batteries and adopting air-independent propulsion, these diesel-electric attack submarines achieved unprecedented submerged endurance, fundamentally changing how Japan protects its waters and competes in the global submarine market.
One of its most distinctive physical features is an X-shaped stern, which combines diving planes and rudders. When they first entered service in 2009, these vessels held the distinction of being the largest displacement submarines used by post-war Japan.
A major breakthrough for the class was the introduction of air-independent propulsion (AIP). By utilizing Stirling engines—licensed from Kockums Naval Solutions and built by Kawasaki Heavy Industries—the Sōryū-class can remain submerged for much longer periods than conventional diesel-electric boats. This capability was further pushed by the eleventh boat in the class, the JS Ōryū, which became the world's first lithium-ion battery submarine. Lithium-ion technology offers nearly double the electric storage capacity of traditional lead-acid batteries, providing a significant advantage in underwater endurance over the slower recharge cycles required by AIP systems.
The class has also become a significant diplomatic tool. Japan offered the Sōryū-class to Australia to replace the Collins-class, a move described as 'extremely impressive' by former Australian Defence Minister David Johnston in 2014. While Australia ultimately chose the French-designed Shortfin Barracuda, other nations including India, Morocco, Norway, Netherlands, and Taiwan have expressed interest. In 2025, reports indicated that the Indonesian Navy was also exploring the potential acquisition of these advanced vessels.
As the JMSDF looks toward the future, the Sōryū-class is being succeeded by the Taigei class, which entered service in 2023. This transition follows a shift in Japanese naval tradition: while previous JMSDF submarines were named after ocean currents, the Sōryū-class introduced a naming convention based on mythological creatures, with Sōryū itself meaning 'blue dragon'.
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- Summary by Intellect · source: Sōryū-class submarine
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