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The Role of ANZUS in Australia’s Reliance on US Extended Nuclear Deterrence

16 Sep 2021
By Anna Hood and Monique Cormier
U.S. Marine Corps C-130J Super Hercules with Marine Aerial Transport Squadron (VMGR) 152 fly over Australia heading to their final destination Brisbane, Australia.  (U.S. Marine Corps photo by MCIPAC Combat Camera Cpl. Sara A. Medina/RELEASED)

Over the last decade, there has been considerable debate about whether the ANZUS Treaty requires Australia to maintain its reliance on US extended nuclear deterrence. This debate is complex, and there are pathways for resolving the legal tensions to which it gives rise. 

In recent years there has been considerable pressure on Australia to relinquish its reliance on US extended nuclear deterrence, which is a key component of Australia’s national security policy. The source of this pressure to come out from under the US nuclear umbrella is twofold. First, Australia is under a legal obligation pursuant to the Nuclear Non-Proliferation Treaty (NPT) to take effective measures with a view to achieving nuclear disarmament. A failure to give up its position under the nuclear umbrella puts Australia at risk of breaching this important obligation. Second, there is an escalating civil society movement to persuade Australia to join the new Treaty on the Prohibition of Nuclear Weapons (TPNW), but this treaty does not allow states parties to maintain a policy of extended nuclear deterrence. 

Despite such pressure on Australia to discard the US nuclear umbrella, politicians from both sides of the aisle have raised concerns that any moves away from extended nuclear deterrence would put the country in violation of the ANZUS Treaty (ANZUS). Article II of ANZUS provides: 

In order more effectively to achieve the objective of this Treaty the Parties separately and jointly by means of continuous and effective self-help and mutual aid will maintain and develop their individual and collective capacity to resist armed attack.

The argument goes that Australia’s withdrawal from the US nuclear umbrella would constitute a breach of its obligation to “maintain and develop [its]…capacity to resist armed attack.”  

At first blush, the idea that article II of ANZUS requires Australia to maintain its policy of relying on US extended nuclear deterrence seems a stretch. Nuclear weapons are not referred to in the text of article II, nor anywhere else in ANZUS. Further, during the negotiation of the treaty it was made clear that states parties to ANZUS were not under any obligations to make specific contributions to the defence of themselves or others to fulfil article II.  

Under international law, however, treaties are not static documents. The rules of treaty interpretation allow for the meaning of treaty terms to change over time. This can occur when states parties have continually and consistently engaged in practices that demonstrate that their understanding of treaty obligations have evolved in a particular way. In the case of ANZUSthere is evidence of state practice to suggest that Australia and the US accept that the meaning of article II of ANZUS has evolved to the point where it requires Australia to remain under the US nuclear umbrella.  

For much of the last 30 years, Australia has consistently and publicly asserted that it is under the US nuclear umbrella and that this policy is connected to its membership of ANZUS. For example, the 2009 Defence White Paper stated that the alliance “means that, for so long as nuclear weapons exist, we are able to rely on the nuclear forces of the United States to deter nuclear attack on Australia,” In 2013, then-Foreign Minister Bob Carr affirmed the belief that ANZUS implies nuclear protection for Australia” and declared, “[i]f you want to abrogate the possibility of us falling under the American nuclear umbrella…you must follow through on that logic. That logic mandates abandoning the ANZUS Treaty.” Such statements suggest that Australia believes the US is providing nuclear protection to Australia because of ANZUS 

At international law, Australia’s assertions are not enough by themselves to alter the scope of article II of ANZUS to require Australia’s ongoing reliance on US extended nuclear deterrence. As the other party to ANZUSthe US must agree or, at the very least, acquiesce to Australia’s position. While there is no publicly available evidence that the US has explicitly endorsed Australia’s interpretation of article II as requiring a nuclear alliance, neither are there any public US statements contradicting Australia’s claims. Given that Australia has consistently and repeatedly asserted for decades that its key security policy of extended nuclear deterrence is a requirement under ANZUS, the fact that the US has been publicly silent on this issue may, according to the rules of international treaty law, be read as acceptance of the Australian view.  

All of this appears to leave Australia in an unenviable international legal position. On the one hand, it is obliged by the NPT to relinquish its policy of US extended nuclear deterrence, which is also necessary for Australia to join the TPNW. On the other hand, ANZUS has evolved to now require Australia to maintain its status under the nuclear umbrella.  

Thankfully there are a number of ways that Australia can navigate through this situation. While ANZUS may currently require Australia to remain under the US nuclear umbrella, the fact that the meaning of treaty terms can evolve through subsequent practice means Australia may again alter the scope of article II. If Australia were to stop publicly proclaiming that ANZUS provides it with nuclear protection or to declare that it no longer intended to be the recipient of US extended nuclear deterrence, then, providing the US did not object to this change in rhetoric, the meaning of article II would shift again and Australia would be free from the nuclear umbrella. Alternatively, Australia could negotiate an explicit agreement with the US for a conventional security alliance, purposely releasing Australia from any obligation or expectation that it remains under the US nuclear umbrella.  

Given the importance of a nuclear-free world to global security, our hope is that Australia reconsiders its interpretation of ANZUS and/or renegotiates the terms of its alliance with the US to allow it to step off the nuclear disarmament side-lines and come out from under the US nuclear umbrella. Not only will this contribute to a safer world, but it will ensure Australia is not in breach of the NPT and is able to join the TPNW. 

For a fuller exposition of the points in this piece, please see Anna Hood and Monique Cormier, “Can Australia Join the Nuclear Ban Treaty Without Undermining ANZUS,” Melbourne University Law Review, 2020.

Dr Anna Hood is a Senior Lecturer at the University of Auckland Faculty of Law. 

Dr Monique Cormier is a Senior Lecturer at the University of New England School of Law.   

This article is published under a Creative Commons Licence and may be republished with attribution.