The revelation that Chinese and Russian submarines have conducted joint patrols in Pacific waters is not merely another footnote in geopolitical rivalry.

It is a trumpet sounding at great volume — warning that the U.S. and its allies may be sleepwalking into a maritime environment increasingly dominated by adversarial undersea cooperation. With quotes now emerging from U.S. defence leadership and congressional analysis, the case against complacency has never been stronger.

According to official reports, China’s People’s Liberation Army Navy (PLAN) and Russia’s Pacific Fleet have recently undertaken coordinated submarine patrols, operating diesel-electric units (so-called Kilo-class submarines) and participating in joint drills and anti-submarine warfare training. Though the scale remains modest — two submarines for now — analysts view the move as representing a new tier of tacit strategic signalling.

Adm. John C. Aquilino, head of U.S. Indo-Pacific Command, has expressed what some in Washington regard as stark concern. In remarks made in Tokyo late in 2023, he said he was “very concerned” about China and Russia’s increasing military collaboration in the Indo-Pacific region, adding that such alignments extend beyond “marriage of convenience.” He noted that when partnered with other adversarial states, including North Korea, this cooperation can accelerate capabilities and generate regional instability.

Meanwhile, U.S. Deputy Secretary of State Kurt Campbell has been urging Europe to raise its voice against the growing Sino-Russian partnership. In a public statement, Campbell affirmed that China has provided “substantial, mostly covert, support to Russia’s military industrial base,” including in submarine technologies. He called for allied governments to synchronise their diplomatic responses and warned that Chinese advances in submarine platforms could erode U.S. undersea dominance.

From the legislative side, Congress has begun integrating these trends into strategy. The Congressional Research Service’s report “China Naval Modernization: Implications for U.S. Navy Capabilities” emphasizes that Congress will review and potentially recalibrate U.S. Navy force structure, procurement and doctrine in light of China’s growing undersea fleet and its cooperation with Russia. Specifically, it argues for increased investment in anti-submarine warfare, unmanned underwater vehicles, and sensor networks to preserve detection and deterrence at depth.

Strategic Implications

With Adm. Aquilino warning that these operations are no longer just symbolic, planners in Washington see increased risk of miscalculation. Joint patrols near waters shared with U.S. allies or those under U.S. watch increase the chances of incidents — submarines misidentified, collisions, or escalation misinterpreted. The U.S. surveillance and early warning forces must respond, but that demands resources, assets and willingness to sharpen readiness.

Historically, the U.S. Navy has enjoyed unmatched advantages in submarine speed, endurance, stealth (especially nuclear-powered submarines), and global reach. Diesel-electric subs lack those endurance advantages, but when deployed closer to shores, especially in concert with allied surface and air assets, they can pose serious anti-sensor threats. The Congressional report warns that China, in particular, is investing heavily in distributed sensors, unmanned underwater vehicles and novel ASW counter-measures. The China-Russia cooperation accelerates this threat curve.

U.S. statements from Deputy Secretary Campbell suggest Washington expects European allies to speak up against these developments. The logic is clear: aligning the diplomatic narrative strengthens deterrence. If China and Russia are allowed to project undersea power without pushback, it becomes harder for alliances (e.g. with Japan, Australia, South Korea) to justify forward basing, naval investment, or even heightened readiness. Meanwhile, Congress is increasingly attentive to budgetary consequences — more ASW capabilities, more sensors, more submarines and support infrastructure. These are expensive undertakings.

Voices from Congress

Congressional reports and testimony are not merely academic. Representative Adam Smith, senior Democrat on the House Armed Services Committee, during a recent delegation to China, stressed to reporters that one of the greatest risks today is “military to military encounters gone wrong”. He underscored that the U.S. must ensure its forces are technically, doctrinally, and logistically prepared for undersea adversaries who are improving rapidly. While that comment was broader in scope, analysts see it as directly relevant to the China-Russia submarine cooperation.

Congressman Dan Sullivan has in past debates characterised joint Chinese-Russian bomber flights and naval patrols as “unprecedented provocations by our adversaries.” He has urged increased defense spending to ensure that U.S. and allied forces can quickly detect, track, and respond to such operations. While much of his focus has been in the air domain, the implications for maritime and undersea strategy are obvious.

Policy Responses: What Washington Should Do

Given these warnings, what actions must the U.S. and its partners take — and soon — if undersea cooperation between China and Russia is to be deterred rather than normalised?

Congress’s interest in unmanned underwater vehicles, enhanced sonar, seabed sensors, and enhanced information sharing must become operational priorities. The U.S. Navy and Defense Department should move new technologies from concept to deployment with fewer lag times.

Allies must be consulted and engaged in visible naval exercises, rotating submarine deterrence patrols, joint training in detection and rescue, and coordinated planning. Japan, Australia, India, Philippines all have maritime interest in presence and deterrence.

To prevent accidents or misinterpretation, protocols for encounters must be clear. U.S. officials have noted the danger of miscalculation in joint operations; clarity boosts deterrence and prevents escalation.

Congress will need to back its words with funding. The CRS report warns that naval shipbuilding, especially nuclear submarines, remains a bottleneck. Delays, cost overruns, and industrial capacity constraints threaten America’s ability to respond to simultaneous challenges in Asia and Europe. Strategic trade-offs are unavoidable unless funding is matched with mission demands.

A Sea Change We Cannot Ignore

The recent China-Russia joint submarine patrols are more than displays of bilateral friendship. They are declarations of strategic intent, experiments in coordination, and potentially the opening moves of a broader maritime competition.

U.S. defence and congressional voices are rightly raising red flags: Adm. Aquilino calls these developments “far beyond a marriage of convenience”; Deputy Secretary Campbell warns allies that China’s advances in submarines could sap U.S. undersea dominance; Congress demands sharper posture, more resources, better deterrence.

What Washington must do is not merely worry, but act — decisively, visibly, and in concert with allies. Because undersea supremacy is not a luxury. It is a linchpin of global deterrence. In the deep waters, delay is not neutral. It is a weakness.

By Bellona Foundation? – Bellona Foundation, Attribution, https://commons.wikimedia.org/w/index.php?curid=5338641