China’s and Russia’s newly intensified naval partnership could embolden China in the South China Sea, where submarine activity is already intense.
Russia and China are natural historical rivals. The Russian tsar and the Emperor of China vied for power in the East for centuries. So did the Soviet Union and Mao Zedong’s China throughout the Cold War. Nevertheless, recent events—most notably the Ukraine War, as well as a long-time commitment to creating a multipolar world that would benefit both Beijing and Moscow more than the existing one—are bringing them together.
Recently, Russian and Chinese submarines conducted a joint patrol in the South China Sea (SCS), a contested zone between China and the Philippines. This historic event, launched as part of Maritime Interaction 2025 exercises in the Sea of Japan, underscores the deepening strategic relationship between Moscow and Beijing as the challenge US dominance across the arc of Eurasia.
China and Russia’s Deepening Military Ties
Since the end of the Cold War, both China and Russia have moved closer together in the realm of military cooperation. Annual joint exercises, such as the Joint Sea series, began in 2012 and have expanded in scope and frequency for more than a decade. Joint surface ship patrols have been routine since 2021, with the fifth annual patrol concluding on August 20 of this year. That patrol covered 6,000 nautical miles in the Pacific. The inclusion of submarines, however, represents an entirely new milestone—signaling advanced interoperability in undersea warfare.
The patrol followed the conclusion of the Maritime Interaction 2025/Joint Sea 2025 drills from August 1-5 in the Sea of Japan, where both navies practiced anti-submarine warfare (ASW) and simulated attacks on enemy vessels. These exercises involved Russian assets such as the destroyer Admiral Tributs and the Kilo-class submarine Volkhov, alongside Chinese vessels like the Shaoxing.
This Sino-Russian naval collaboration is purportedly part of the broader “no limits” partnership declared by President Vladimir Putin of Russia and Chinese President Xi Jinping in February 2022, shortly before the invasion of Ukraine. Joint activities have even included a number of bomber patrols near Alaska and naval transits near US allies, like Japan and the Philippines, amplifying perceptions of a new axis challenging the post-WWII order.
Russia and China Each Have Cutting-Edge Submarines
Russia and China’s joint submarine patrol involved the Russian Pacific Fleet Project 636.3 Varshavyanka-class (an improved Kilo-class) diesel-electric submarine and Volkhov, known for its quiet operation and advanced sonar systems, capable of launching Kalibr cruise missiles. The Chinese counterpart was part of an unarmed Chinese People’s Liberation Army Navy (PLAN) diesel-electric submarine, likely from the Yuan-class (Type 039A), which features air-independent propulsion for extended submerged endurance and is optimized for coastal defense in the Indo-Pacific.
Launched immediately after the Sea of Japan surface naval exercises, the patrol traversed the Sea of Japan and into the East China Sea, monitoring maritime traffic and protecting economic interests such as oil routes and fishing grounds. Russian state media reported the operation as a resounding success in enhancing mutual trust and operational coordination, with both submarines operating in tandem to simulate defensive scenarios. While not explicitly entering the SCS, the patrol’s proximity to disputed areas like the East China Sea—where China claims the Senkaku islands—adds to the strategic weight.
The mission lasted several weeks, concluding earlier this week, and was described as a step toward “joint maritime security” in the region.
Experts note that diesel-electric submarines like these are ideal for littoral operations in shallow waters, making them potent in flashpoints, such as the SCS. This patrol demonstrates Russia’s export of submarine technology to China, including quieting technologies, bolstering Beijing’s undersea fleet, which already numbers over 60 boats.
Tensions Are Heating Up in the Indo-Pacific
The timing of this patrol coincides with heightened frictions in the SCS, a vital waterway through which $3.4 trillion in global trade passes annually. China asserts expansive “nine-dash line” claims over 90 percent of the sea—overlapping with exclusive economic zones of Vietnam, Malaysia, Brunei, and the Philippines. Recent incidents include Chinese coast guard vessels ramming Philippine resupply ships at Second Thomas Shoal in June of this year, as well as aggressive maneuvers against US Navy P-8 Poseidon aircraft.
America has responded to these provocations with freedom of navigation operations (FONOPs) and joint drills with partners, such as the Philippines and Japan. In July, the US and Philippines conducted their largest-ever Balikatan exercises, simulating island defense amid fears of Chinese invasion tactics. Russia’s involvement, though indirect, signals a potential “anti-access/area-denial” (A2/AD) strategy, where joint submarine patrols could deter US carrier groups in a Taiwan contingency.
China’s and Russia’s newly intensified naval partnership could embolden China in the South China Sea, where submarine activity is already intense. The US Indo-Pacific Command has increased anti-submarine surveillance, deploying assets like the Virginia-class submarines and P-8 aircraft. As tensions rise, the joint patrol raises questions about escalation risks, including accidental collisions in crowded waters.
America must begin to engage in deft diplomacy as it relates to the other two poles of the new tripolar world system. Of the two opposing powers, it is clear which is the longer-term threat. Unless Washington ends the Ukraine War and tries to accommodate Russia within the new system—and in so doing works to return China and Russia to their historic hostility—America will find itself outmanned and outgunned across Eurasia.
About the Author: Brandon J. Weichert
Brandon J. Weichert is a senior national security editor at The National Interest. Recently, Weichert became the host of The National Security Hour on America Outloud News and iHeartRadio, where he discusses national security policy every Wednesday at 8pm Eastern. He is also a contributor at Popular Mechanics and has consulted regularly with various government institutions and private organizations on geopolitical issues. Weichert’s writings have appeared in multiple publications, including The Washington Times, National Review, The American Spectator, MSN, The Asia Times, and others. His books include Winning Space: How America Remains a Superpower, Biohacked: China’s Race to Control Life, and The Shadow War: Iran’s Quest for Supremacy. His newest book, A Disaster of Our Own Making: How the West Lost Ukraine is available for purchase wherever books are sold. He can be followed via Twitter @WeTheBrandon.
Image: Shutterstock / Aleksandr Merkushev.
