Australia and Japan should split the burden of protecting critical sea lines of communication (SLOC) in the Pacific. In an ASPI special report published today, Japan-Australia defence cooperation in the Pacific: The case for a partial division of labour, I argue that this will be necessary to reinforce deterrence now and prepare for the growing possibility of a regional war instigated by China. In such a conflict, the United States would likely be focused on fighting China and would expect allies to shoulder much of the burden of protecting their own supply chains.

If it becomes too risky to pass through the Malacca, Sunda and Lombok straits in a conflict, the long route around Australia and through the Vitiaz Strait between the islands of Papua New Guinea becomes a vital sea lane to bring fuel and other supplies to Northeast Asia. If that north-south sea lane were cut by China—which it would have greater capacity to do if the Chinese military could operate from Pacific island bases—it could render Japan unable to continue fighting effectively, which could decide the course of the war. The same logic applies to South Korea and Taiwan.

The report divides the Pacific into four zones and highlights which areas matter most for Australia’s and Japan’s strategic interests. Geography dictates that Japan must pay more attention to countering China in Micronesia, where it works closely with the US, while Australia should play a more prominent role working with New Zealand in Polynesia. Japanese and Australian interests overlap most substantially in Melanesia. The case for coordination is greatest in PNG and Solomon Islands, which both bracket or run parallel to the key SLOC between the east coast of Australia and Japan, forming a chokepoint.

The report makes several key recommendations, including:

—Australia and Japan should engage the US in joint contingency planning for a wartime division of labour, with the Trilateral Defence Ministerial Meeting serving as the primary coordination mechanism. As a secondary priority, consultations should extend to South Korea, the Philippines and Taiwan.

—Australian and Japanese ministers and officials should look for opportunities to raise conflict-preparedness issues privately with Pacific governments. While each country will often engage Pacific partners separately, their messaging should be coordinated.

—To manage some of the risks and sensitivities of such discussions, think tanks and research institutions could also play a helpful role, including through the expansion of track 1.5 mechanisms, which involve government officials as well as non-government experts, to engage Japan, Australia and the wider Pacific. ASPI has led the way doing this.

—Australia should help Japan deepen its engagement with existing mechanisms for regional security cooperation, such as the Joint Heads of Pacific Security Meeting and the South Pacific Defence Ministers’ Meeting, while being mindful not to establish pathways into these forums that China could attempt to follow.

—Australia could help lay the groundwork for Japan to establish a defence attache in Port Moresby. While the decision rests solely with PNG and Japan, Australia’s close defence ties with both countries mean it would form part of the discussion.

Australia and Japan must work patiently with Pacific countries, respecting and supporting their sovereignty, to achieve these goals. Any public declaration of a division of labour would be cited by critics, including Chinese Communist Party propagandists, as evidence that Australia and Japan supposedly retain a colonial mindset and are carving the region into spheres of influence without regard for Pacific agency.

Even so, the strategic contours of a division of labour could be discernible and effective without being openly acknowledged. Pacific leaders already recognise that some countries focus more on certain parts of the Pacific, as New Zealand does in Polynesia. Many senior figures are also raising concerns about Beijing’s aims and activities, as PNG’s Minister for Defence Billy Joseph did at ASPI’s Defence Conference in June.

The Trump administration’s National Security Strategy has allayed concerns about US retrenchment in the Indo-Pacific. Even so, Canberra and Tokyo will be in a stronger position and have greater agency if they work together to secure their maritime connections to the world. This is the crux of the case for their greater defence cooperation in the Pacific.