Australia needs to take into account three important issues if AUKUS were to bring peace and stability to Southeast Asia. First, Australia should build trust with its Southeast Asian neighbours, especially those critical to AUKUS’ success. Second, Australia must ensure AUKUS’ compliance with international law. Third, Australia should commit to building a peaceful and stable relationship with China.

AUKUS supporters in Australia argue that it will bolster stability in the Asia Pacific by deterring China’s growing military influence in the region. But critics argue that Australia should pursue more strategic security cooperation with its Asia Pacific neighbours rather than its traditional Western allies.

Chief among AUKUS critics’ concerns is Southeast Asia’s reaction. Like other contentious regional issues, Southeast Asian countries are not unanimous on AUKUS. The Philippines seems to welcome the trilateral arrangement and so are Vietnam and Singapore, albeit implicitly. Indonesia and Malaysia are more critical.

This is hardly surprising. The Philippines, Vietnam and Singapore have traditionally welcomed extra-regional military presence, while Indonesia and Malaysia have been wary. Indonesia’s discomfort even goes back to its first president, Sukarno. It is in Australia’s interest to gain its neighbours’ trust. Suspicion — particularly in Indonesia, one of Australia’s most important neighbours — will undermine Australia’s efforts to build deeper ties with the region.

Ensuring transparency and strengthening communication is crucial. Australia is trying to improve communication with its Southeast Asian counterparts after they were shocked by AUKUS’ lack of prior consultation.

In February 2023, Indonesian Foreign Minister Retno Marsudi and Defence Minister Prabowo Subianto met with Australian Minister for Foreign Affairs Penny Wong and Minister for Defence Richard Marles to discuss strategic security issues in the Indo-Pacific. AUKUS was high on the agenda with Indonesia reiterating ‘the importance of transparency in AUKUS cooperation and … a commitment to nuclear non-proliferation’.

After the release of AUKUS’ Joint Leaders Statement in March 2023, the Australian Chief of Navy Vice Admiral Mark Hammond went on a Southeast Asian tour and met with Admiral Muhammad Ali, the Chief of the Indonesian Navy in Jakarta. Following their meeting, Admiral Ali stated in a public lecture that the Indonesian Navy believe that AUKUS will comply with international law. While concerns remain, Indonesia has softened its tone.

Australia has also improved transparency by outlining its AUKUS strategy in the latest Defence Strategic Review. Intense communication and transparency are the best way to regain and retain Southeast Asia’s trust.

Complying with international law is also important. Australia has emphasised that these nuclear-powered submarines will not carry nuclear weapons. AUKUS will not violate the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and comply with all International Atomic Energy Agency (IAEA) safeguards.

But there are ongoing discussions at the IAEA and NPT on whether the transfer of nuclear material to Australia potentially violates the transfer of nuclear explosive devices obligation, thereby violating the IAEA and NPT safeguards. Australia has responded by reiterating that it does not seek to build any nuclear weapons-capable submarines.

Aside from meeting its nuclear treaty obligations, Australia must also comply with the United Nations Convention on the Law of the Sea (UNCLOS) rules on the passage of submarines. Australia’s nuclear-powered submarines will likely pass through Indonesian Archipelagic Sea Lanes, something that worries members of the Indonesian parliament.

Under UNCLOS rules of Archipelagic Sea Lanes passages, innocent passages and transit passages, Australia’s nuclear-powered submarines can pass through Indonesian waters in times of peace. But each passage carries different obligations. The submarines can remain submerged when passing through the designated Archipelagic Sea Lanes of Indonesia or the straits typically used for international navigation. But they must surface and show their flag when passing through territorial waters or non-designated archipelagic waters.

Observing UNCLOS rules is important for Australia to gain Indonesia’s trust as its immediate neighbour. Violating them may lead countries in the region to perceive Australia as a threat to regional stability.

Australia must commit to a peaceful relationship with China too. Counterbalancing China’s growing dominance may be beneficial, but an escalating Australia–China tension is one of Southeast Asia’s biggest concerns.

Shortly after the AUKUS announcement in September 2021, Malaysian Prime Minister Ismail Sabri Yaakob said that AUKUS might ‘provoke other powers to take more aggressive action in [the] region, especially in the South China Sea’. The concern about China’s increased aggression is likely shared by all Southeast Asian countries, even those that welcome AUKUS.

How Australia and China can work out their differences peacefully will be key to maintaining peace and security in the region.

AUKUS may provide a solution to China’s intimidatory actions in the region. But China is one of Southeast Asia’s most important economic partners, even if it is in Southeast Asia’s interest to have the United States and its allies — including Australia — as reliable partners. Any Australia–China conflict would be disastrous for the region.

Building and maintaining Southeast Asian trust through Australian transparency and compliance with international law will be critical to managing the delicate balance of deterring China without escalating tension.

Aristyo Rizka Darmawan is a PhD Scholar at The ANU College of Asia and the Pacific at The Australian National University and a Lecturer in International Law at Universitas Indonesia.

An extended version of this article appeared in the most recent edition of East Asia Forum Quarterly, ‘An age of sanctions’, Vol 15, No 2.