Japan Institute for National Fundamentals
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Speaking out

Maki Nakagawa

【#1282】China-Russia Military Cooperation Expanding Undersea

Maki Nakagawa ／ 2025.09.04 (Thu)


September 1, 2025

　
The Chinese and Russian navies conducted a joint exercise, dubbed Joint Sea 2025 by China and Maritime Interaction 2025 by Russia, around the Vladivostok military port in the Russian Far East from August 1 to 5, followed by their joint surface ship patrol in the Western Pacific and their joint submarine patrol in the Sea of Japan and the East China Sea from August 6 to 20. This is the first time that a joint submarine patrol by Chinese and Russian has been reported.

First joint submarine patrol

According to the Joint Staff of the Japanese Ministry of Defense, a guided-missile destroyer and a submarine rescue ship of the Chinese Navy sailed through the Tsushima Strait from the Sea of Japan to the East China Sea on August 13 before a frigate, a submarine, and a rescue tug of the Russian Navy did so on August 14 and 15. All of them participated in the joint exercise through August 5. The Russian Navy ships sailed north through the strait August 20 or later, returning to Russia.

“Diesel-electric submarines of the Russian Navy and the Chinese People’s Liberation Army Navy have conducted a joint patrol in the Asia-Pacific region for the first time in history,” reported Russia’s TASS news agency on August 27. “The [Russian] submarine covered over 2,000 nautical miles during its voyage.”

China has not yet released any reports regarding the joint submarine patrol, but China apparently cooperated with Russia in its effort to counter the United States, as U.S. President Donald Trump announced on August 1 the deployment of two nuclear submarines in “appropriate regions” in response to provocative remarks by former Russian President Dmitry Medvedev.

China and Russia have been expanding joint military exercises since 2012, when they conducted their first joint exercise. They launched joint air patrols in 2019 and joint sea patrols in 2021, before conducting their first joint undersea patrol this time around.

Submarines usually act alone because their undersea communications can risk exposing their locations. Therefore, during the latest patrol, Chinese and Russian submarines might have coordinated areas and schedules for patrolling and patrolled separately before sharing marine information (regarding seabed topography and surface layers, sea currents, water quality, etc.) and acoustic information (such as submarines’ unique acoustic fingerprints) they collected through patrolling. They might have not cooperated physically in underwater operations.

Information sharing to improve Chinese military capabilities

However, Russian submarines are generally considered to have higher acoustic intelligence collection capabilities than Chinese submarines because they are quieter than Chinese ones.

If the latest joint submarine patrol leads China-Russia military cooperation to cover the underwater domain in addition to air and sea surface domains and develop their permanent information and intelligence sharing framework, China may be allowed to access Japanese and U.S. military vessels’ acoustic data that Russia has collected and compiled since the Soviet era.

This may improve China’s capacity to gather and identify information on Japanese and U.S. vessels and contribute to China’s “area-denial” strategy to deny Japanese and U.S. operations in the Sea of Japan and the East China Sea within the first island chain that runs from the Japanese archipelago to Taiwan and the Philippines. We must be vigilant about the deepening of military cooperation between China and Russia.

Maki Nakagawa is a researcher at the Japan Institute for National Fundamentals and a former commander of the Basic Intelligence Unit, Japan Ground Self-Defense Force.