On 27 September 1991, US President George H.W. Bush addressed the nation ^[1] to announce a milestone in nuclear disarmament, which included the full withdrawal of shorter-range nuclear weapons—so-called tactical, theatre or non-strategic weapons—from US Navy vessels and foreign countries, albeit with some caveats in Europe.

Bush’s bold action rested on the assumption of an improving strategic environment, including reciprocal arms reductions by the Soviet Union, which were continued by Russia, Ukraine and other Soviet successor states for a while after 1991. It also assumed that the remaining US nuclear forces would be sufficient to deter an attack on the US or its allies, including Australia. Today, Chinese and Russian actions are undermining those assumptions, with dangerous implications.

Confronting the growing risk of nuclear war ^[2], Australia is rightly working with Japan and others to rejuvenate global momentum on non-proliferation and disarmament. This is vital work. But such efforts can only succeed if the international community recognises the positive role that the US nuclear umbrella—more formally called extended deterrence—continues to play in limiting the spread of nuclear weapons and calls out destabilising conduct by China and Russia.

To appreciate the contribution to non-proliferation made by the US nuclear umbrella, we need to understand its purpose and form.

Early in the Cold War, forward-deployed nuclear weapons were focused on deterrence and warfighting, compensating for the numerical superiority of communist armies. As Soviet capabilities improved and more countries became nuclear powers, the purpose of the US nuclear umbrella expanded to include non-proliferation.

In essence, the US preferred to protect key allies like Japan rather than risk them developing their own arsenals. US and allied interests broadly aligned because all sides feared a multipolar arms race in which small, independent arsenals could be vulnerable to pre-emptive first strikes, while the custodial risks of accidental or unauthorised use were multiplied. Building independent nuclear capabilities would have also strained allies’ economic and financial resources. It would also have been unpalatable to the public in some countries, like Japan. The same logic applies now.

Australia is an interesting case in point. Having cooperated with Britain’s nuclear program, Australia engaged in a renewed debate ^[3] about developing its own capability after China’s first nuclear test in 1964. In the end, the credibility of US security guarantees helped inform Canberra’s decision to eschew pursuit of nuclear weapons and ratify the Nuclear Non-Proliferation Treaty in 1973.

The protection-for-abstinence bargain propping up the nuclear umbrella relies on allies and adversaries believing that the US has the will to risk nuclear retaliation against the homeland to defend distant friends. Even today, a handful of NATO allies ^[4] host small quantities of sharable US nuclear weapons on their territories to improve the credibility of deterrence.

But nuclear sharing is a European exception. In the Indo-Pacific, Bush’s announcement ended an era in which US nuclear weapons had been present ^[5] in allied territories for decades, either as deployments on land or in transit on US Navy vessels. Following earlier withdrawals in the 1970s from Okinawa (ahead of its full return to Japan), Taiwan and the Philippines, the US removed its last nuclear weapons from South Korea in 1991. Managing these forward deployments strained public trust and involved levels of secrecy and backroom dealings that are still emerging in the archives ^[6].

It’s possible that contingencies still exist for redeploying tactical nuclear weapons to forward locations in the Indo-Pacific. But, in the main, South Korea and Japan put their faith in public proclamations ^[7] that the US has the means and will to project nuclear force from afar in their defence, illustrated by the periodic appearance in the region of US nuclear-capable bombers. Behind the scenes, bilateral consultations ^[8] on extended deterrence thrash out details and align expectations.

Successive Australian defence white papers ^[9] dating back to 1994 make clear that Australia also expects US nuclear protection, even if Canberra seems less concerned than Seoul or Tokyo about soliciting US assurances in public. Australia banned the stationing of nuclear weapons on its territory under the Treaty of Raratonga ^[10] in 1986. However, the periodic operation of US bombers from Royal Australian Air Force Base Darwin and longstanding shared access to intelligence and communication facilities in Australia, including Pine Gap and North West Cape ^[11], attest to an implicit quid pro quo that the price of coverage by the US nuclear umbrella includes integration in nuclear planning and therefore the likelihood of being targeted. The same is true for Japan and South Korea.

Despite the implicit costs, the US nuclear umbrella has remained attractive to allies because the alternatives have seemed unpalatable, at least during the phase after the Cold War when the risk of nuclear war felt relatively low.

Japan and South Korea are among the countries sometimes called latent nuclear powers ^[12] because they probably possess the means to develop nuclear capabilities relatively promptly. This would be harder for Australia but not impossible ^[13], at least in theory. In practice, the economic, legal and political barriers to independently going nuclear remain prohibitive, and the Australian public is set against it ^[14]. As strategists like Hugh White have argued ^[15], the main driver for Australia or other US allies in the Indo-Pacific to overcome these hurdles in pursuit of nuclear weapons would be a breakdown of trust in US protection.

In other words, the US nuclear umbrella remains a lynchpin of non-proliferation in our region. As Australia’s 2017 foreign policy white paper says ^[16], ‘Without extended deterrence, more countries in the Indo-Pacific would need to re-assess their security and defence capabilities.’ That is official code for seeking weapons of mass destruction.

Unfortunately, allies will be watching Chinese and Russian actions and pondering whether the US nuclear umbrella remains credible.

China under President Xi Jinping is rapidly expanding its nuclear forces ^[17] and doing so outside an effective arms control regime. Unlike the US, Beijing is modernising its forces without any transparency, which violates its obligations ^[18] as a nuclear weapons state under the Non-Proliferation Treaty. Russia is not alone in deploying new weapons ^[19] platforms that have potential nuclear applications, such as hypersonic missiles. But intentions and trustworthiness matter as well as the capabilities themselves, which is why President Vladimir Putin’s flagrant nuclear threats over Ukraine and obstructionism in multilateral forums ^[20] put Moscow in a different category to Washington. Chinese and Russian nuclear forces have cooperated ^[21] to some extent since the announcement of the Xi–Putin ‘no limits’ partnerships. Both countries have close ties to nuclear North Korea, which continues to test and improve its own nuclear forces.

So, how should Australia and the international community respond to our worsening strategic environment?

For a start, we mustn’t give up on international rules and norms or shy away from criticising China and Russia for fear of being labelled biased.

In this light, it was heartening to see Foreign Minister Penny Wong prioritise non-proliferation initiatives ^[22] and messaging ^[23], including calling out Moscow and demanding more from Beijing, during UN high-level week this month. Equally, Australian officials have said they want to work with the International Atomic Energy Agency to set the highest possible non-proliferation standards through the acquisition of nuclear-powered (not nuclear-armed) submarines under the AUKUS partnership. Such engagement has been welcomed by IAEA Director General ^[24] Rafael Grossi. Given Japanese Prime Minister Fumio Kishida’s personal commitment to non-proliferation, there are opportunities for Canberra and Tokyo to work more closely together, including through the Non-Proliferation and Disarmament Initiative ^[25], which they co-founded.

Importantly, we mustn’t dislocate multilateral initiatives from strategic realities. This is one reason why Australian and Japanese leadership makes sense—both bring perspectives as, to quote the foreign policy white paper, nations that ‘rely on nuclear deterrence for their security’.

We have an opportunity to apply this more joined-up style of thinking as the US works with its allies to develop the concept of integrated deterrence ^[26], which is a key component of the US national defence strategy ^[27]. In line with the nuclear posture review, nuclear forces are being modernised. Overall, however, nuclear weapons should play a reduced role ^[28] in maintaining credible extended deterrence. Instead, more emphasis shifts onto conventional and hybrid capabilities, leveraging the US network of allies and partners. This would support non-proliferation if it can be achieved.

Consistent with integrated deterrence, Australia, Japan and South Korea are already investing in capabilities like conventional long-range strike and offensive cyber. For Australia, AUKUS is crucial ^[29] for achieving this—not just for submarines but also in the other areas of advanced technology cooperation. South Korea has perhaps gone the furthest by introducing a new command structure to implement the ‘three-axis’ system ^[30], which is intended to deter a North Korean nuclear attack through a combination of missile defence and conventional strike. These investments by US allies are intended to complement rather than supplant the US nuclear umbrella, which, in theory, is made more credible by becoming more clearly a last resort.

We don’t yet know how integrated deterrence will work in practice, but it seems evidently better for the cause of non-proliferation than other options being mooted to address the credibility of extended deterrence, such as reintroducing US nuclear weapons ^[31] to the Korean peninsula or allies pursuing sovereign nuclear capabilities.

We would all prefer to see a world with fewer nuclear weapons. In our current strategic circumstances, that requires finding a way to incorporate the non-proliferation benefits of the US nuclear umbrella into multilateral initiatives.