Henderson dry dock: Why Australia’s nuclear submarines can’t arrive until the floating dock is ready

Completing the sophisticated floating dry dock for Western Australia’s Henderson Defence Precinct is a vital condition Australia must meet to obtain and operate its planned fleet of nuclear-powered and conventionally armed attack submarines (SSNs).

Having the ability to safely repair nuclear submarines that are damaged or which require major maintenance that can’t be done at sea or at their moorings is essential to meet tough local and international nuclear safety requirements and to satisfy very rigorous standards for nuclear submarines which were set decades ago by the United States.

Under the AUKUS agreement involving the US, United Kingdom and Australia, Washington is to provide Australia with three Virginia-class attack submarines. More submarines, styled SSN AUKUS, will be jointly designed and built by the UK and Australia. It has not been decided yet how many SSN AUKUS boats will be built for the Royal Australian Navy. They’ll be constructed at the Osborne shipyard in South Australia.

Britain and the US are both struggling with manufacturing and maintenance levels for their own submarine forces and one of many questions hanging over the AUKUS submarine plan is whether the US will decide they can afford to sell Virginias to Australia, or if that would leave the US Navy short of boats. As well, the UK submarine production and maintenance process is lagging badly and the hope is that Australia’s involvement in the SSN AUKUS program will help build momentum.

Australia has already made major financial contributions to beef up both the US and UK design and production processes.

The RAN has also sent scores of its submariners to train further on US and British submarines, including qualifying to work on their nuclear elements.

In the meantime, there will be a strong nuclear-powered submarine presence in WA with up to four boats from the US and one from the UK making regular lengthy visits to HMAS Stirling, about 60km south of Perth, as Submarine Rotational Force – West, from 2027.

During preliminary visits, US submarines have already undergone maintenance that has helped take the pressure off overstretched American facilities. That work has also given Australians crucial experience working on nuclear-powered vessels to progressively build a sovereign nuclear submarine sustainment capability.

The floating dry dock will enable a much higher level of maintenance. It’s a massive structure which rides on the surface. When a submarine or surface ship needs serious work on its hull, the dock’s buoyancy is reduced and it settles into the water until it is low enough for the vessel to enter it. Then the dock’s buoyancy is increased again and it rises, lifting the craft it is carrying clear of the water.

The planned dock will be easily able to accommodate future versions of the US Virginia-class submarines and SSN AUKUS which are likely to be over 10,000 tonnes.

In late July this year, the Federal Government announced that it had selected long-time submarine and maritime engineering specialists Leidos Gibbs and Cox Australia to design the floating dry dock to support Australia’s planned SSN fleet.

Deputy Prime Minister and Defence Minister Richard Marles and Defence Industry Minister Pat Conroy said the company’s selection would ensure that the dock would be ready to carry out critical repairs on, and maintenance of, the Royal Australian Navy’s SSNs from the early 2030s, and major “depot level” maintenance from the late 2030s. That includes major refits at key points in the SSNs’ lives.

“Having this contingency dry dock capability is a pre-condition for Australia to receive its first Virginia-class submarine from the US and will provide a critical contingency capability for Australia and its partners,” the ministers said.

These vital maintenance capabilities would be established in accordance with domestic processes and regulatory requirements, and consistent with Australia’s international obligations to maintain the highest standards for nuclear safety, security and safeguards. In addition to supporting a strong, sovereign industrial base, a contingency dry dock capability would be vital to ensuring Australia could sustain and operate its future submarine fleet and work with its partners in the US and UK to support security and stability across the Indo-Pacific region, the ministers said.

Leidos said the floating dry dock would be a critical component of Australia’s nuclear submarine infrastructure and would enable system inspections, maintenance and repair out of the water. The company said the dock’s design was complex because of the specialised nuclear safety and security requirements.

Under the direction of the Australian Submarine Agency, it would deliver the first phase of a functional design by mid-2027, Leidos said.

In 2025, the Federal Government invested an initial $12 billion to deliver the Defence Precinct at Henderson. It said those facilities and other AUKUS and shipbuilding commitments would support 10,000 direct jobs over the next two decades in WA.

In 2024, the Federal parliamentary standing committee on public works examined plans to build the extensive infrastructure to accommodate the submarines. Defence officials told the committee that the 2020 Defence Strategic Update and the 2020 Force Structure Plan identified the need for Australia to invest in “high-end capabilities that bolster deterrence and better prepare Australia to respond in the event of conflict in the region”.

The officials said the need for conventionally armed, nuclear-powered submarines had arisen as Australia’s strategic environment had deteriorated.

“The Indo-Pacific region is now the centre of strategic competition,” they said.

“As a three-ocean nation dependent on seaborne international trade, Australia requires cutting-edge naval capabilities.”

The parliamentary committee noted that establishing the Henderson precinct facilities would involve dredging, incurring destruction in a unique area within the Perth metropolitan area.

“Cockburn Sound and Garden Island are sensitive ecosystems which are made up of critically endangered ecological communities, highly endemic plant species, migratory species, priority fauna species and diverse and significant marine species.”

The committee said Defence stated that the works would be designed to minimise impacts on listed threatened ecological communities. Elements of the works that may significantly impact the environment would be referred to the environment minister.

Apart from the nuclear submarine facilities, the Henderson precinct will house support infrastructure for Australia’s conventionally powered Collins-class submarines and surface combatant vessels, and construction facilities for the army’s heavy landing craft and the navy’s fleet of Japanese Mogami-class frigates.

The submarine agency has said HMAS Stirling will be the operational base for the RAN’s future submarine fleet and will carry out “in-water” maintenance.