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.

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........

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