Japan’s Sōryū-Class ‘Blue Dragon’ Submarine Is a Naval Powerhouse

Key Points – Japan’s Sōryū-class diesel-electric attack submarines, commissioned from 2009, form the current backbone of the JMSDF’s undersea fleet, succeeding the Oyashio-class.

-These highly capable and stealthy submarines initially featured Air-Independent Propulsion (AIP) using Stirling engines for extended submerged endurance.

-Notably, the final two boats of the twelve-strong class pioneered the operational use of advanced lithium-ion batteries, offering superior endurance and faster charging.

-Equipped with an X-shaped rudder for maneuverability, a comprehensive sonar suite, Type 89 torpedoes, and Harpoon missiles, the Sōryū-class serves as a vital deterrent in the Asia-Pacific, though it is now being succeeded by the Taigei-class.

Sōryū-Class: Inside Japan’s ‘Blue Dragon’ Submarines with AIP & Lithium Power

The Sōryū-class is the current backbone of Japan’s submarine fleet. The subs were built as an evolution and replacement to the aged Oyashio-class submarines. First commissioned by the Japanese Maritime Self-Defense Force in 2009, the Sōryū-class remains one of Japan’s stealthiest and most capable submarines to date.

Despite their growing age and planned replacement, the Sōryū-class submarines are still considered by many to be some of the most capable subs of their category.

Creation of the “Blue Dragon”

The development of the Sōryū-class was initiated to replace the aging Oyashio-class submarines. Built by Mitsubishi Heavy Industries and Kawasaki Shipbuilding Corporation, the Sōryū-class was designed to meet the growing demands of undersea warfare in the Asia-Pacific region. The name “Sōryū,” which means “Blue Dragon,” which is a shift in JMSDF naming conventions from ocean currents to mythological creatures. Interestingly, the name also pays homage to the World War II aircraft carrier Sōryū, which was sunk during the Battle of Midway.

In terms of physical characteristics, the Sōryū-class submarines are approximately 84 meters in length, with a beam of 9.1 meters and a draught of 8.5 meters. When surfaced, they displace around 2,900 tons, and when submerged, this increases to about 4,200 tons. These submarines are manned by a crew of 65, including both officers and enlisted personnel. They can reach speeds of up to 13 knots on the surface and 20 knots while submerged. Their operational range is estimated at 6,100 nautical miles at a cruising speed of 6.5 knots, particularly when using their air-independent propulsion (AIP) systems.

One of the most notable features of the Sōryū-class is its propulsion system. It was the first Japanese submarine class to incorporate AIP technology, which allows the vessel to remain submerged for extended periods without surfacing. This system uses Stirling engines, licensed from Sweden’s Kockums Naval Solutions and manufactured by Kawasaki Heavy Industries. The AIP system significantly enhances the submarine’s stealth by reducing the need to surface frequently, thereby minimizing the risk of detection.

Japan’s Stealthy Killing Machines

However, starting with the eleventh boat in the series, JS Ōryū, the JMSDF began transitioning from AIP to lithium-ion battery technology. This made the Sōryū-class the first operational submarine in the world to use lithium-ion batteries. These batteries offer several advantages over AIP systems, including faster charging times, greater energy density, and improved endurance during high-speed underwater operations. Additionally, lithium-ion batteries require less maintenance and contribute to a cleaner internal environment, which has reportedly improved the quality of life for the crew during extended missions.

The Sōryū-class submarines were built to be as stealthy as possible. The hull is coated with anechoic tiles that absorb sonar waves, thereby reducing the submarine’s acoustic signature. Internally, the submarine is equipped with soundproofing materials to minimize noise from machinery and crew activities. Another distinctive feature is the X-shaped rudder configuration, which replaces the traditional cruciform design. This configuration enhances maneuverability, especially in shallow waters, and reduces the risk of damage when the submarine is resting on the seabed. It also improves control during low-speed operations, making the vessel more agile and responsive.

Additionally,  Sōryū-class is equipped with a comprehensive suite of sensors and combat systems. These include the ZPS-6F radar for surface and low-level air search, and the Hughes/Oki ZQQ-7 sonar suite, which comprises bow-mounted sonar, flank arrays, and a towed array sonar. The submarine also features electronic warfare systems such as the ZLR-3-6 electronic support measures (ESM) and is equipped with 3-inch underwater launchers for deploying acoustic device countermeasures (ADCs). These systems enable the submarine to detect, track, and engage enemy vessels with high precision while maintaining situational awareness in complex underwater environments.

In terms of armament, the Sōryū-class is outfitted with six 533 mm torpedo tubes located in the bow. These tubes can launch Type 89 heavyweight torpedoes, UGM-84 Harpoon anti-ship missiles, and naval mines. The submarine can carry up to 30 reloads, allowing it to engage a wide range of targets, from enemy submarines to surface ships. This versatile armament makes the Sōryū-class a formidable platform for both offensive and defensive operations.

Why Japan Still Needs the Sōryū-Class

As the backbone of the JMSDF’s submarine fleet, the Sōryū-class plays an important role in Japan’s naval strategy. With rising tensions in the East and South China Seas, these submarines serve as a powerful deterrent against potential adversaries.

Their ability to operate silently and remain submerged for extended periods makes them ideal for surveillance, reconnaissance, anti-submarine warfare, anti-surface warfare, and special operations support. The mere presence of a Sōryū-class submarine in contested waters can restrict enemy naval movements and complicate strategic planning, embodying the concept of a “fleet-in-being.”

Each Sōryū-class submarine costs approximately 540 to 600 million US dollars, depending on the configuration and year of production. A total of twelve submarines were built between 2005 and 2019, and all are currently active in the JMSDF fleet. These submarines are a significant investment in Japan’s maritime security and underscore the country’s commitment to maintaining a robust and reliable naval force.

The Sōryū-class is now being succeeded by the Taigei-class submarines, which build upon and improve the technological advancements of their predecessors.

Despite their age and replacement, the Sōryū-class is set to stay in service for at least another decade before they are slowly phased out.

However, the Sōryū-class still remains as one of Japan’s best attack submarines and is still a capable force to be reckoned with.

About the Author

Isaac Seitz, a Defense Columnist, graduated from Patrick Henry College’s Strategic Intelligence and National Security program. He has also studied Russian at Middlebury Language Schools and has worked as an intelligence Analyst in the private sector.

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