First Joint Russian–PRC Submarine Exercise Patrols Pacific

Executive Summary:

• Russia and the People’s Republic of China (PRC) held the joint Maritime Interaction-2025 naval drills on August 1–5 in the Sea of Japan and East China Sea, coordinating submarine operations for the first time.
• These drills demonstrate a new level of interoperability in exercises on anti-submarine warfare, air defense, and maritime patrols, featuring surface ships, submarines, and naval aviation.
• The Maritime Interaction joint exercises, which began in 2012, and the Northern Interaction joint exercises, which began in 2021, demonstrate robust Russia–PRC military cooperation, bolstering their “no limits” strategic partnership established in early 2022.
• Moscow and Beijing framed the drills as a direct response to U.S. military presence in the Asia-Pacific, signaling closer Russia-PRC military alignment alongside their deepening economic relations, which intensified in the aftermath of Russia’s full-scale invasion of Ukraine.

On June 19 at the St. Petersburg International Economic Forum, Russian President Vladimir Putin announced joint Russia–People’s Republic of China (PRC) military exercises (Kommersant, June 19). Putin remarked, “This is extremely important to guarantee stability in world affairs … We regularly conduct exercises and will conduct them this year” (President of Russia, June 19). Two months later, the Russian Pacific Fleet press center broadcast that the joint Russian–PRC Maritime Interaction-2025 annual naval exercise, which the PRC calls Joint Sea 2025, would be held in the Sea of Japan from August 1–5. Besides surface ships, the exercise included diesel-electric submarines and naval aviation (Telegram/@TOF_VMF, July 30). After the maneuvers ended, the two navies deployed two diesel-electric submarines at the end of August in their first joint underwater maneuvers in the Sea of Japan and East China Sea, with each boat accompanied by a surface warship and submarine rescue vessel (RIA Novosti, August 27).

The Russian Pacific Fleet said that after its mission, which covered 2,000 nautical miles, the Project 636.3 Varshavianka-class Volkhov submarine returned to its naval base in Vladivostok (RIA Novosti, August 27). The People’s Liberation Army Navy (PLAN) did not specifically mention the submarine patrol but reported that the joint exercise occurred in the sea and airspace near Vladivostok and involved submarine rescue tasks, stating that the theme of the drill was “jointly safeguarding strategic maritime routes” and “jointly countering security threats in the western Pacific” (Global Times, July 30). While the PRC did not specify which of its submarines was involved, the U.S. Naval Institute identified it as a Kilo-class Russian-built boat, which was purchased from Russia in the 1990s (Military Watch Magazine, July 31; U.S. Naval Institute, August 28).

The Russian Pacific Fleet press service claims that the main objectives of Maritime Interaction-2025 were the strengthening of naval cooperation, maintaining peace and stability in the Asia-Pacific region, monitoring the marine environment area, and protecting Russian and PRC maritime economic activity infrastructure (RIA Novosti, August 7). Xinhua noted that during the drills, the Russian and PRC navies fired artillery and practiced anti-submarine and air defense maneuvers in the Sea of Japan, adding, that participating PRC naval vessels and various Russian naval vessels “formed a joint formation to conduct maritime joint patrol in an area of the western Pacific” (South China Morning Post, August 20).

Russian experts emphasized that joint underwater maneuvering is a complex operation that requires the highest level of training. Rear Admiral Mikhail Chekmasov commented on the joint patrol, “The Russian and Chinese sides have not conducted such events before, and I do not remember practicing such things with foreign submarines. This is a very complex process” (Izvestiia, September 1).

Russia and the PRC had to carefully plan joint naval underwater navigation, as submarine communications and navigation are more complex than surface operations. Submarines operate in three-dimensional space, in conditions of the sea’s complex and shifting hydrology, making their ability to maintain clear contact between submarines more difficult. Communication is only possible through underwater hydroacoustic communication, which has limitations in range and speed of information exchange (Izvestiia, September 1).

The Maritime Interaction-2025 patrol follows years of expanding joint exercises. Since 2018, the PRC’s People’s Liberation Army (PLA) has participated in several large-scale Russian drills, including Vostok-2018, Tsentr-2019, and Kavkaz-2020 (see EDM, October 3, 2018, September 26, 2019, September 23, 2020). By 2022, the PRC’s involvement in joint exercises with Russia had broadened to include its army, navy, and air force in Vostok-2022, which spanned 13 training sites across Russia and extended into the Sea of Japan (Caspian News, August 28; see EDM, September 14, 2022).

The bilateral exercises parallel those of the Russian military. From September 10–16, 2024, Russia held its largest strategic military exercises, Okean-2024, since the collapse of the Soviet Union in the Arctic, Pacific, Mediterranean, Caspian, and Baltic. The Russian Defense Ministry reported that more than 90,000 military personnel, over 400 warships, submarines, and auxiliary fleet support vessels, more than 120 aircraft and helicopters of the naval aviation of the Navy and the Aerospace Forces, about 7,000 units of weapons, and special equipment took part in Okean-2024 (RIA Novosti; Telegram/@mod_russia, September 10, 2024). The  Okean-2024 exercises occurred in the same month as the Russia–PRC Northern Interaction-2024 drills in the Sea of Japan and the Sea of Okhotsk (Deutsche Welle, August 3). Putin explicitly stated that the Okean-2024 exercise was a response to demonstrate opposition to increased U.S. naval deployments in the Pacific, claiming, “With their aggressive actions, the U.S. is seeking to achieve a tangible military advantage, thereby breaking the existing security architecture and balance of power in the Asia-Pacific region” (President of Russia, September 10, 2024).

The 15-day Northern Interaction-2024 patrol was the fifth in an annual naval series that began in 2021, as Russia and the PRC steadily strengthen their “no limits” strategic partnership declared in early 2022. Later in 2022, Russian General Staff Chief Valerii Gerasimov echoed Putin’s earlier comments, declaring that Russia’s bilateral military exercises with the PRC were motivated by the U.S. military’s increased presence in the Pacific (Interfaks, August 7).

The exercises occurred amid preparations for the Shanghai Cooperation Organization (SCO) summit, held in Tianjin from August 31 to September 1 (see EDM, September 2). At the SCO summit, General Secretary of the Chinese Communist Party (CCP) Xi Jinping and Putin again reiterated that their countries intend to deepen their relations. The SCO summit was followed by a massive military parade in Beijing on September 3 to commemorate the 80th anniversary of victory over Japan in World War II. Foreign governments carefully monitored this parade for signs of new weaponry, with naval analysts noting new anti-ship missiles and undersea drones on display for the first time (see China Brief Notes, August 28). Most worrying for the U.S. Navy presence in the western Pacific was the unveiling of hypersonic nuclear-capable, long-range missiles (Global Times, September 3).

Russia and the PRC have held joint naval patrols every year since the Maritime Interaction exercises began in 2012. The exercises are held in different regions, with the host country alternating. In 2024, the exercise occurred in the South China Sea. During this year’s Maritime Interaction exercise, the Volkhov submarine simulated an underwater accident, running aground in Peter the Great Bay. The PLAN’s rescue ship, Xihu, established contact with the crew and used its LR-7 underwater vehicle to simulate its evacuation (RT TV, August 5). The Xihu is the PLAN’s latest type of comprehensive rescue ship that was commissioned in early 2025. Retired PRC naval officer Wang Yunfei remarked that the involvement of submarines in the exercises highlighted the deepening of PRC–Russian military ties (Izvestiia, August 7).

The same day that Maritime Interaction-2025 began, U.S. President Donald Trump responded to Deputy Chairman of the Russian Security Council Dmitri Medvedev’s warning to the United States about Russia’s Dead Hand. Some military analysts interpreted this as a reference to Perimeter, a Cold War-era semi-automatic system designed to guarantee a retaliatory nuclear strike even if a first strike destroys Russia’s top command. In response, Trump declared that he deployed two nuclear submarines into tactical positions “just in case [Medvedev’s] foolish and inflammatory statements are more than just that” (The Washington Post, August 1; Kommersant, August 8).

Some U.S. commentators have expressed a misunderstanding of Russia’s naval priorities. In a recent op-ed published the month before the Maritime Interaction-2025 naval exercise,  Lieutenant Colonel Jeffery M. Fritz, an Armor officer serving in Estonia with the U.S. Army Security Assistance Command (USASAC), proposed that the United States buy the Commander Islands from Russia for $15 billion to monitor potential PRC submarine activity attempting to enter the Arctic Ocean. The Commander Islands lie at the far western end of the Aleutians. Fritz wrote:

By transferring the islands, Russia could subtly complicate China’s strategic calculus in the Arctic without directly confronting Beijing. This would allow Moscow to recalibrate the regional balance in favor of a multipolar Arctic, one where no single non-Arctic power dominates while extracting significant economic value and potentially resetting diplomatic channels with the West (Breaking Defense, July 28).

Spokeswoman Maria Zakharova observed, “This is not worth commenting on in principle, since selling out the Motherland in our country is considered both legally and by conscience one of the most terrible crimes,” suggesting that instead of buying the Arctic islands, the United States spend the money on paying down the national debt (Kommersant, July 29).

Russia and the PRC have been rivals since Soviet times, but the countries have since come closer due to deepening economic relations, intensified in the aftermath of Russia’s full-scale invasion of Ukraine and its attendant Western sanctions, reinforced by their shared long-standing commitment to creating a multipolar world. More frequent Russia–PRC maritime patrols and exercises, now including joint submarine operations, force the West to consider the possibility of united Russian–PRC military and naval action in the event of a war in the Pacific, possibly over Taiwan. In the interim, Putin claims that U.S. deployments in the Pacific are driving Russian–PRC military cooperation (President of Russia, September 10, 2024). The impact of the use of submarines in joint Russia–PRC naval activities remains unclear, but marks a new level of interoperability in Russia and the PRC’s underwater warfare techniques, multiplying the difficulties for future Western anti-submarine forces operating in the world’s largest ocean.