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Westport Threatens AUKUS
A United States Virginia-class fast-attack submarine alongside at HMAS Stirling, Western Australia, with commercial tugs on either side

Cockburn Sound, Western Australia

Western Australia is building a container port beside the submarine base America is spending billions to use.

The project is called Westport. It moves Western Australia’s container terminal to Kwinana and rebuilds it as an automated port, about six kilometres across the water from HMAS Stirling, the base where United States nuclear submarines will rotate under AUKUS.

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Watch the campaign video

Watch: what is at stake in Cockburn Sound

Just over a minute on why a state infrastructure decision made before AUKUS existed is now a question about American submarines.

What this campaign is asking Congress to do

Support a provision in the National Defense Authorization Act restricting commercial container port development within ten miles of critical international military assets, including allied bases hosting United States nuclear submarines.

Three things a decision made in Perth does to American assets

Each figure is sourced and explained in full on the Evidence page.

Schematic map of Cockburn Sound, Western AustraliaCockburn Sound runs north to south for about twenty kilometres. Garden Island forms its western side and carries HMAS Stirling, the naval base where United States nuclear submarines will rotate under AUKUS, toward the southern end of the island. The Western Australian mainland forms the eastern side. The proposed submarine maintenance facility at Henderson sits on that mainland shore to the north, and the Westport project would build an automated container terminal further south at Kwinana, about six kilometres across the water from the submarine base. The sound has a single narrow navigable entrance, at its northern end through Gage Roads, used by submarines and commercial shipping alike. The commercial shipping channel runs south from that entrance to the proposed terminal. The submarine transit route runs across the sound between HMAS Stirling and the maintenance facility at Henderson, and the two routes cross. The southern end of the sound is not navigable by large vessels, and Garden Island is reached from the mainland by a causeway.about 6 kmHMAS StirlingUS and UK submarinesrotate hereGardenIslandHendersonproposed submarinemaintenance facilityWhere they crosscontainer ships would crossthe submarine transit routeKwinanaproposed Westport automatedcontainer terminalSubmarine transit routeCommercial shippingchannelThe single narrow entrancein and out, through Gage RoadsFremantle, about20 km northCockburn SoundcausewaySouthern end not navigableIndianOceanN
Schematic, not to scale. Garden Island carries HMAS Stirling, the base where United States submarines will rotate. The Westport automated container terminal would be built at Kwinana, on the mainland shore opposite. Both submarine and commercial traffic use the single narrow northern entrance, and the shipping channel to the terminal crosses the submarine transit route to the maintenance facility at Henderson. The geography is set out in full on The Threat.

  • 6 km

    The commercial docks would sit six kilometres from the submarine base

    Westport moves Western Australia's container terminal to Kwinana, on the eastern shore of Cockburn Sound, and builds it as an automated terminal. HMAS Stirling, where US Virginia-class submarines will rotate, is directly across the water. Vessels waiting at anchor can sit closer still.

  • One channel

    The container ships would cross the submarines' own transit route

    Cockburn Sound has one navigable entrance, and every submarine movement and every commercial movement passes through it. Inside the sound it gets worse: the route submarines take between HMAS Stirling and their maintenance facility at Henderson runs straight across the shipping channel serving the new terminal. Traffic through that water is projected to more than double.

  • 15 ships

    Almost none of that shipping is Australian

    Australia has fifteen Australian-flagged commercial vessels over 2,000 tons. Virtually every ship transiting the sound beside the submarines is foreign-flagged, with the visibility and vetting that implies.

Figures from the August 2025 assessment by Air Vice-Marshal John Blackburn AO (Retd) and Commodore Vince Di Pietro AM CSC RAN (Retd). Every source is listed on the Evidence page.

The ships would not just share the door. They would cross the corridor.

The submarine base is on Garden Island, on the western shore. The maintenance facility planned for those submarines is at Henderson, on the mainland to the north. Boats moving between the two cross Cockburn Sound, from one side to the other, as a matter of routine.

The shipping channel serving the proposed terminal runs down that same water. The two routes intersect. A wider entrance does not fix it and a second channel does not fix it, because the conflict is created by where the terminal is put, not by how the water is approached.

How the crossing conflict works

Understand the threat

What Westport is, where it sits relative to the submarine base, and why the combination puts American assets and American spending at risk.

Read the threat assessment

Take action

The National Defense Authorization Act ask, stated plainly, with everything you need to raise it in a congressional office or a newsroom.

See the ask

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