SSN-AUKUS explained

The nuclear-powered attack submarine that Australia and the UK will both build and operate, based on a UK design with US technology.

Explainer · Updated 26 October 2026

SSN-AUKUS is the long-term centrepiece of AUKUS Pillar 1. It is the submarine Australia will build in Adelaide and operate from the 2040s, and the boat the UK will use to replace its current fleet. This page covers what is publicly known about the design, the builders, the timeline and the agreements behind it.

"SSN" is the naval designation for a nuclear-powered attack submarine. The 2023 White House fact sheet used it throughout, and said Australia's future submarine would be called "SSN-AUKUS" [1].

A UK design with US technology

When the plan was announced on 13 March 2023, the three governments said SSN-AUKUS would be based on the United Kingdom's next-generation submarine design while incorporating cutting-edge US submarine technologies [1]. The Prime Minister's release added that it would also incorporate Australian technologies [4].

The fact sheet said bringing proven US technology into the design would improve the "capability, commonality and interoperability" of all three nations' nuclear-powered submarines [1].

The UK Government said the SSN-AUKUS boats would be "the largest, most advanced and most powerful attack submarines ever operated by the Royal Navy" [2].

Who will operate it

SSN-AUKUS will be the future attack submarine for both Australia and the United Kingdom [1]. In the UK, the new boats will replace the current Astute-class submarines [2]. In Australia, they follow the Virginia-class boats bought from the US in the 2030s. See our Virginia-class explainer.

The Prime Minister's release said the submarines would be an Australian sovereign capability, "commanded by the Royal Australian Navy and sustained by Australians in Australian shipyards" [4].

Who builds it

In the UK. Construction of the UK's boats will take place principally at Barrow-in-Furness, with BAE Systems and Rolls-Royce building them [2]. Rolls-Royce will supply the nuclear reactors for all UK and Australian SSN-AUKUS submarines [3].

In Australia. Australia's boats will be built at a future Submarine Construction Yard in Adelaide, South Australia [1]. A parliamentary committee reported that in March 2024 the Government selected ASC Pty Ltd and BAE Systems Australia to build them at the Osborne shipyard [7]. Our Osborne explainer covers the yard.

The UK Government said some components for Australia's boats would be made in the UK [2].

Timeline

According to the 2023 plan:

Australia and the UK intend to start building SSN-AUKUS in their own shipyards before the end of this decade [1].
The UK intends to deliver its first SSN-AUKUS to the Royal Navy in the late 2030s [1].
Australia plans to deliver its first Australian-built SSN-AUKUS to the Royal Australian Navy in the early 2040s [1].

The UK Government repeated those dates when it awarded design contracts in October 2023 [3]. The full sequence is on our submarine timeline.

Contracts and investment so far

£4 billion in UK design contracts (Oct 2023). On 1 October 2023 the UK Ministry of Defence signed the Detailed Design and Long Leads phase with BAE Systems, Rolls-Royce and Babcock. The contracts, totalling £4 billion, cover design, prototyping and buying the main long-lead components for the first UK boats [3].
Infrastructure in the UK. The same announcement said the Barrow shipyard and the Rolls-Royce reactor site at Raynesway, Derby, would be developed and expanded where needed [3].
£6 billion UK commitment (2025). The May 2026 AUKUS ministerial statement noted "GBP 6 billion that the UK committed in 2025" as part of the investment behind SSN-AUKUS progress [6].
Australian investment in the UK. The 2023 fact sheet said Australia committed to a proportionate financial investment in the UK submarine industrial base to speed up SSN-AUKUS production [1].

In May 2026 the three defence ministers "acknowledged significant progress in the design and delivery of SSN-AUKUS" [6].

The Geelong Treaty

On 26 July 2025, Australia and the UK signed the Nuclear-Powered Submarine Partnership and Collaboration Treaty, known as the Geelong Treaty [5]. The two governments described it as a commitment for the next 50 years of UK-Australian defence cooperation under AUKUS Pillar 1 [5].

The treaty covers cooperation on the design, build, operation, sustainment and disposal of SSN-AUKUS submarines. It also supports the workforce, infrastructure and regulatory systems Australia needs, and the rotation of a UK Astute-class submarine through HMAS Stirling [5]. The joint statement said it is consistent with both countries' nuclear non-proliferation obligations [5].

Key terms

D2L2. Detailed Design and Long Leads, the UK contract phase signed in October 2023 [3].
Long-lead components. Major parts that take years to make, ordered early so construction can start on time [3].
Astute class. The UK's current attack submarines, which SSN-AUKUS will replace in the Royal Navy [2].
Geelong Treaty. The 2025 Australia-UK treaty on SSN-AUKUS cooperation [5].

Conventionally armed

SSN-AUKUS is described as a conventionally armed, nuclear-powered submarine [1][4]. Nuclear power refers to the reactor that drives the boat, not its weapons. Australia has committed that it does not and will not seek nuclear weapons [1]. Our non-proliferation explainer sets out the safeguards.

Frequently asked questions

Who designed SSN-AUKUS?

It is based on the UK's next-generation submarine design, with US submarine technology and, according to the Australian Government, Australian technology too [1][4].

Where will Australia's SSN-AUKUS submarines be built?

At the Submarine Construction Yard at Osborne in Adelaide, South Australia [1][7].

When will the first SSN-AUKUS be ready?

The UK plans to deliver its first in the late 2030s, and Australia plans to deliver its first Australian-built boat in the early 2040s [1].

Sources

Checked 26 Oct 2026. AUKUS Defense is an independent site, not affiliated with any government. Plans and figures may change; check the sources above for the latest.