Pacific allies move to blunt China's undersea push

Global Watch | 2026-05-18

As China's undersea mapping activities expand across the Pacific, Australia, Japan and the Philippines are responding with greater urgency.

What began as focused survey work near the First Island Chain -- Pacific Ocean archipelagos extending from Kamchatka to the Malay Peninsula -- now reaches much farther afield, including waters near Hawaii and even the Arctic, according to Reuters, mirroring a wider pattern in which undersea competition increasingly stretches from the Indo-Pacific into the High North and other strategic chokepoints.

That wider pattern matters because it points to a longer-range naval ambition, not just localized data collection around Taiwan.

The shift is already changing regional planning.

Governments that once treated undersea competition as a narrow naval issue are now folding it into broader debates about deterrence, infrastructure security and alliance coordination.

In practice, that means more patrols, more surveillance and more money flowing into defense at a time when many Indo-Pacific states would rather spend it elsewhere.

Regional defense buildup

Australia has become central to that response.

Under AUKUS -- a trilateral security partnership between Australia, the United Kingdom, and the United States -- HMAS Stirling, a naval base situated on the west coast of Australia, is being prepared for a rotational presence of U.S. and U.K. nuclear-powered submarines beginning in 2027, while allied maintenance and sustainment work is already moving forward.

In February 2026, the U.S. Navy said activity at HMAS Stirling was about building "a network of trusted partners" able to sustain undersea forces "forward, at speed and at scale."

That is more than logistics. It is a deliberate effort to thicken allied presence in the eastern Indian Ocean and the approaches to Southeast Asia.

Japan is reinforcing its own posture at the same time.

The Japanese Ministry of Defense has confirmed that the guided missile destroyer JS Chokai is being modified and its crew trained in the United States to acquire Tomahawk launch capability, part of Tokyo's broader push to strengthen long-range strike options.

At the same time, Japan continues to invest in persistent maritime surveillance, including P-1 and P-3C patrol aircraft and expanding regional exercises with partners.

The Philippines, meanwhile, is moving from exposure to active coordination.

Manila and Washington conducted a maritime cooperative activity within the Philippine exclusive economic zone (EEZ) in March.

Reuters also reported that the Philippines, the United States and Australia had completed another round of joint drills in the South China Sea, with Australia contributing P-8A Poseidon surveillance aircraft.

These moves do not erase the pressure on Philippine waters. They do, however, show that undersea competition is being met with a more routine allied presence.

For smaller Pacific island states, the picture is less reassuring.

Great-power competition can bring security attention, but it can also complicate EEZ management, raise commercial risk and deter tourism and infrastructure investment.

The result is a harsher trade-off between national development and strategic exposure.

Enduring allied edge

China's mapping campaign is ambitious, but it still runs into a structural disadvantage.

The United States and its allies are operating in a maritime environment they have watched, exercised in and integrated across for decades.

Reuters quoted former Royal Australian Navy submarine chief Peter Scott as saying Chinese mapping data would be "potentially invaluable in preparation of the battlespace." But that point cuts both ways: these are waters already embedded in allied planning, surveillance and anti-submarine operations.

That is where the real balance still lies. The advantage is not just in platforms. It is in networks.

Australia's P-8 fleet, Japan's maritime patrol and surveillance architecture, U.S. undersea infrastructure and the habits of intelligence-sharing across alliances create a denser operational picture than China can generate alone.

In other words, Beijing may be making the seafloor more legible, but it is doing so in a theater where its competitors still have the more mature system.

That does not mean the challenge is minor, just that the response is already underway.

China's undersea ambitions are growing, but so is the regional effort to contain the strategic advantages those surveys are meant to produce.

For now, the balance below the waves still favors the side with the broader coalition, the deeper experience and the more resilient web of surveillance and access, a pattern reinforced by the wider emphasis on interoperability, burden-sharing and undersea deterrence across allied maritime strategy.