Geelong Treaty Explained: UK-Australia 50-Year Defence Deal on AUKUS Submarines

Australia and the United Kingdom have signed a landmark 50-year bilateral defence agreement—formally named the Geelong Treaty—cementing their long-term commitment under the AUKUS alliance, even as the United States undergoes an internal review of its role in the trilateral pact.

The treaty was signed on 26 July 2025 during the UK-Australia Defence Ministers’ Meeting in Geelong, Victoria, by Australia’s Deputy Prime Minister and Defence Minister Richard Marles and UK Defence Secretary John Healey.

The Geelong Treaty, officially titled the Nuclear-Powered Submarine Partnership and Collaboration Treaty, represents a historic, half-century commitment under AUKUS Pillar I—the component of the AUKUS pact focused on nuclear-powered submarine capability development.

The treaty outlines comprehensive cooperation between the UK and Australia in the design, construction, operation, sustainment, and eventual disposal of a new class of SSN-AUKUS submarines.

SSN-AUKUS refers to a planned fleet of next-generation, conventionally armed but nuclear-powered submarines. “SSN” is NATO terminology for “Ship Submersible Nuclear” attack submarines.

As per the agreement, the submarines will integrate technology contributions from all three AUKUS partners (Australia, the UK, and the US). The UK plans to build its vessels in northern England for the Royal Navy, while Australia will construct its submarines in South Australia, specifically at the Osborne Naval Shipyard, for delivery in the 2040s. To support this ambitious undertaking, the Geelong Treaty also facilitates extensive training programs in the UK for Australian submariners and defence personnel and commits to developing the required workforce, infrastructure, and regulatory systems within Australia.

Another key aspect of the treaty includes enabling a rotational presence of the UK’s Astute-class submarines at HMAS Stirling in Western Australia, as part of the Submarine Rotational Force – West. This rotation will enhance Australia’s operational readiness while bridging capability gaps until its own SSN fleet is operational.

Furthermore, the treaty establishes what Marles described as a “seamless defence industrial base” between the UK and Australia. This integration will allow Australian companies to contribute to submarine construction in the UK, and vice versa. As a result, the treaty is projected to create tens of thousands of jobs across both nations and strengthen bilateral defence industry supply chains, supporting economic growth and sovereign capability development.

Importantly, the Geelong Treaty aligns with international nuclear non-proliferation obligations, including:

• The Treaty on the Non-Proliferation of Nuclear Weapons (NPT),

• The South Pacific Nuclear Free Zone Treaty and its protocols,

• Australia’s safeguards agreements with the International Atomic Energy Agency (IAEA),

• and the AUKUS Naval Nuclear Propulsion Agreement (ANNPA).

Together with the ANNPA, the Geelong Treaty forms the legal and operational backbone of the SSN-AUKUS program, which aims to deliver cutting-edge undersea capabilities in both the Indo-Pacific and the Euro-Atlantic, promoting regional stability for decades to come.

However, this bilateral momentum comes at a time of uncertainty from the third AUKUS partner—the United States. The US Department of Defense, under the new Trump administration, has initiated a review of the AUKUS agreement to determine whether it aligns with the “America First” agenda. This review is being led by Elbridge Colby, the Pentagon’s Undersecretary of Defense Policy, who has previously expressed skepticism about AUKUS, raising concerns it could overstretch US naval resources and leave American sailors exposed.

Despite this wavering stance, UK Foreign Secretary David Lammy, speaking at Sydney’s Lowy Institute, emphasized that the Geelong Treaty was not an act of stepping in for a retreating America but rather a step toward a robust and secure long-term partnership. He described the agreement as part of a “new era of instability” and noted that “investing in defence is an investment in peace”, reinforcing that all participating governments—including the UK and Australia—regularly conduct such reviews for major defence procurements.

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Marles, meanwhile, highlighted the treaty’s role in showing that “AUKUS is happening, it is happening on time, and we are delivering it.” He confirmed that Australia would contribute approximately $4.6 billion to support both British and American shipbuilding industries under the broader $368 billion AUKUS submarine program, which also includes the purchase of at least three US-made Virginia-class nuclear-powered submarines starting in the early 2030s.

Although the text of the Geelong Treaty has not yet been released publicly, it will be tabled in Parliament next week, further solidifying transparency and legislative oversight.

In sum, the Geelong Treaty marks a defining moment in UK-Australia defence relations, strengthening trilateral security cooperation, deepening industrial and strategic ties, and reinforcing the Indo-Pacific’s balance of power—regardless of short-term political headwinds in Washington.

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