The battle beneath Australia’s seas

9 June 2026 | Jennifer Parker

*Originally published in The Australian Defence Supplement on 2 June 2026

Image: The first Speartooth LUUV is handed over to the US Navy at C2 Robotics’ Melbourne site. From left, RAN Navy’s Directorate of Maritime Integrated Capabilities Captain Tony Miskelly, C2 Robotics chief executive Troy Duggan, and US defence attache in Canberra, Captain Josh Fagan, USN. Picture: C2 Robotics

Australia is critically dependent on infrastructure lying on the ­seabed. More than 95 per cent of our international data traffic travels through subsea cables, alongside the pipelines and energy infrastructure that underpin the economy.

As the maritime domain becomes increasingly contested, the battle beneath the oceans is intensifying. Chinese naval deployments around Australia are reminders that control of our ­surrounding seas can no longer be assumed, and we should apply the same assumption to the underwater domain.

Undersea cables, seabed infrastructure and the systems used to monitor and protect them are now part of strategic competition. That growing vulnerability helps explain Australia’s increasing investment in undersea warfare capabilities, including systems such as Ghost Shark and Speartooth. While significant gaps remain in areas such as hydrography and mine warfare, investments in capabilities including AUKUS, the Hunter-class frigate’s towed array sonar, the Bluebottle uncrewed surface vessels with towed array sonars, and uncrewed underwater vehicles should provide Australia with the greatest underwater situational awareness capability it has ever possessed.

What happens in the underwater domain, and our ability to respond to developments there, is understandably shrouded in secrecy. But in April, British Defence Secretary John Healey provided a rare public glimpse into this contest when he de­classified a Russian operation inside the United Kingdom’s Exclusive Economic Zone.

The operation involved a Russian Akula nuclear-powered submarine and two specialist vessels from Moscow’s Main Directorate for Deep Sea Research, which Healey said are designed to survey underwater infrastructure in peacetime and sabotage it in conflict. The UK has every reason to be concerned following a series of attacks on undersea cables and pipelines in the Baltic Sea.

But the capability to interfere with subsea cables, pipelines and broader seabed infrastructure is rapidly expanding. China is investing heavily in undersea capabilities, from sensors and uncrewed underwater vehicles to increasingly sophisticated submarines. In 2025, considerable attention was given to reports that Chinese researchers had developed a deep-sea cable cutter capable of severing cables at depths of up to 4000m. Chinese-flagged vessels, and vessels crewed by Chinese nationals, have been suspected of interfering with several subsea cables servicing Taiwan.

The growing accessibility of uncrewed underwater vehicles (UUV) also means state and non-state actors increasingly have the ability to surveil and interfere with critical underwater infrastructure.

Key to underwater domain awareness is understanding where your vulnerabilities lie and maintaining strong maritime domain awareness above the surface. Many recent incidents involving undersea infrastructure have not involved submarines at all, but ­surface vessels dragging anchors across cables and pipelines.

Monitoring one of the world’s largest maritime domains is an immense challenge, made harder by Australia’s fragmented maritime security architecture spread across multiple agencies and without a dedicated coastguard.

Amid this growing competition, Australia does appear to be leaning more heavily into undersea warfare capabilities. In 2024, the government projected that undersea warfare would account for 17 per cent of the Defence Integrated Investment Program (IIP) over the decade.

In 2026, that figure increased to 23 per cent, the single largest proportional investment area.

Much of this investment is driven by Australia’s nuclear-powered submarine program, although the full scope of Australia’s undersea capabilities likely remains classified. Still, there are some public ­indicators. The government has announced a $1.7bn investment in the Ghost Shark extra-large autonomous underwater vehicle, and an undisclosed investment in the smaller, much more affordable Speartooth large uncrewed underwater vehicle (LUUV) which is optimised for seabed warfare and agile undersea operations, reaching areas Ghost Shark cannot.

Manufacturers C2 Robotics last month also delivered the first of a batch of Speartooth LUUVs to the US Navy. And late last year, the US Navy ordered a variant of Ghost Shark to demonstrate delivery of large payloads across extended ranges underwater.

The full capabilities of Ghost Shark and Speartooth remain unclear publicly, but Defence has promoted their potential roles in intelligence, surveillance, reconnaissance, logistics and strike. Taken together, these capabilities should significantly strengthen Australia’s broader undersea warfare posture.

This investment is also supported by the 2023 acquisition of ADV Guidance, a converted civilian vessel intended to support undersea operations.

In any future regional conflict, and potentially well short of conflict, Australia’s critical undersea infrastructure will be targeted. Protecting it requires Australia to understand activity both above and below the sea. That demands a genuinely integrated maritime security architecture, clear responsibilities across government, and the capability to detect and respond to threats.

Australia’s maritime security system remains fragmented and, at least publicly, responsibilities for protecting subsea infrastructure are far from clear. But from a capability perspective, Australia does appear to be leaning into ­elements of the challenge through investments in Hunter-class frigates, uncrewed underwater vehicles and broader undersea warfare capabilities.

Australia is finally beginning to invest seriously in understanding and operating in the underwater battlespace. Given the nation’s dependence on critical seabed infrastructure, that investment is long overdue.