Marles says the seabed is a “battlefield”. But should militaries lead the fight?

I just spent the weekend at the Shangri-La Dialogue in Singapore. I have been researching submarine cable security for years, and often felt like I was making the case to people with more pressing things to worry about. This year was different. Cable security ran through plenary sessions, bilateral meetings and corridor conversations with an urgency that I hadn’t encountered before. Something has shifted in how seriously governments are taking this issue, and Singapore was where that shift became visible.

The centrepiece came from Australia’s Defence Minister Richard Marles. He told delegates that over the past 18 months, the world has witnessed “attacks” against subsea critical infrastructure “at a scale and frequency that is historically unprecedented”. He pointed to specific incidents – cables severed in the Baltic Sea, a tanker that dragged its anchor for nearly a hundred kilometres, damaging power connectors and telecommunications lines. He called undersea cables the arteries of modern civilisation and was unflinching about Australia’s exposure: a nation whose internet traffic flows almost entirely through a handful of cables, among the most vulnerable in the world. “We have been slow – collectively slow – to recognise them [submarine cables] as the strategic targets they have become,” Marles told the audience.

He was right. And the weekend produced tangible responses to match the rhetoric. Singapore led the launch of GUIDE – the Guiding Principles for Underwater Infrastructure Defence Exchanges – a 17-country cross-regional framework spanning Southeast Asia, Europe, Oceania and the Gulf, designed to facilitate information sharing and practical defence cooperation on critical underwater infrastructure. Separately, the United States, United Kingdom and Australia announced a new AUKUS project to develop underwater drone technology explicitly to protect undersea cables – a “signature project” of AUKUS Pillar Two. Taken together, this represents the clearest alignment of political will around cable security I have witnessed beyond Europe. The issue has well and truly arrived in the Indo-Pacific.

But arrival brings its own complications. There is a tension sitting inside these announcements that received far less attention than it deserves.

Principle 4 of the GUIDE framework, signed by all 17 countries in Singapore, states that defence establishments play complementary and supporting roles. Civilian authorities and private operators bear primary responsibility for the design, regulation, installation and repair of secure, reliable and resilient subsea infrastructure. That is not a minor caveat – it is the agreed basis on which this grouping of states decided to organise themselves on this issue.

When a defence minister declares the seabed a battlefield and a pact of countries announces military drones as its flagship response, public expectations shift accordingly. The issue becomes a military story. And that risks crowding out the civilian work that will predominantly determine whether Australia’s cables are secure – domestic repair capacity, route diversity requirements, regulatory frameworks, cable landing station security, liability regimes for damage. These are the unglamorous solutions. They are also the central ones. Australia currently has virtually no domestic cable repair capability. That gap will not be closed by underwater military drones.

What military support looks like in practice remains unanswered. When a cable is sabotaged in Australia’s jurisdiction, who calls whom? What is the actual remit of the ADF and Maritime Border Command, and where does it end? How does military surveillance hand off to civilian repair operations?

GUIDE is voluntary and non-binding, and the United States, Japan and China – the three powers whose behaviour most directly shapes network resilience – were absent from the signatory list. The framework is a genuine start. It is not yet an architecture.

Marles’s speech was the most consequential framing of this issue by any Australian official to date, and the political momentum coming out of Singapore is real and welcome. But momentum needs direction. Translating this weekend into policy means being precise about what military capability can and cannot solve – and building the civilian regulatory and infrastructure response with the same urgency being applied to the military one. Drones and defence frameworks matter. So does knowing who actually picks up the phone when a cable goes dark, and whether anyone built the civilian systems to answer the call.