Executive summary
- China’s growing military capabilities and patterns of coercion along the First Island Chain — a geographic construct stretching from the northern tip of Japan into littoral Southeast Asia, encompassing Taiwan and the Philippines — are the primary focus of growing defence cooperation between Australia, Japan and the United States (AJUS). To counter these activities, the three countries are pursuing a strategy of deterrence by denial, attempting to make the costs of military action too prohibitive for China to contemplate.
- The AJUS countries have developed a robust roadmap for operationalising that shared approach across information-sharing, defence industrial cooperation, integrated air and missile defence, air and maritime operations, and other important areas. Important progress is being made across all these metrics, including the creation of new trilateral information-sharing and policy consultation mechanisms, more frequent and sophisticated trilateral exercises and operations, and closer coordination on defence production and technology development challenges.
- For these initial efforts to make credible contributions to collective deterrence, the AJUS countries must grapple with a range of complex challenges. This includes deciding on appropriate divisions of labour in different operational contexts; reconciling differing political thresholds for the use of military force; better understanding how national capability acquisition priorities or shortfalls may affect trilateral operational planning; and agreeing upon acceptable levels of integration across command and control and information sharing.
- This report presents the views of four policy thinkers and professionals from across the three countries on the current state of trilateral deterrence by denial across the First Island Chain, identifying a range of policy-relevant implications as AJUS moves to implement its collective regional military strategy. These include:
- The First Island Chain might be a useful construct for geographically bounding a trilateral deterrence strategy, but would be highly unlikely to contain a high-end conflict should deterrence fail.
- Whether in deconflicting national efforts or pursuing collective planning, the three countries will need to set realistic expectations about their respective political thresholds for committing and using coordinated and/or combined force in a range of different scenarios.
- To mitigate political impediments to integration, experts suggest that the three countries should prioritise the development of operational integration, rather than simply fixating on a ‘gold standard’ of a unified command and control (C2) structure.
- AJUS should double down on collective resilience measures — secure communications, heightened cybersecurity, contested logistics and supply chain diversification — to support both peacetime deterrence and potential wartime operational requirements.
- Effectively implementing denial along the First Island Chain — let alone across the wider region — will almost certainly require a broader coalition than AJUS alone, even if the trilateral remains the ‘core’ of a high-end military strategy.
Introduction
Tom Corben
Research Fellow, Foreign Policy and Defence, United States Studies Centre
Of all the traditional security challenges confronting Australia, Japan and the United States in the Indo-Pacific, few occupy greater attention than those posed by China’s growing military capabilities and patterns of coercion along the First Island Chain (FIC) — a geographic construct stretching from the northern tip of Japan into littoral Southeast Asia, encompassing Taiwan and the Philippines. Granted, China continues to rely primarily on civilian and ‘grey zone’ tools and tactics, rather than kinetic force, to achieve its aims. Yet policymakers in Canberra, Tokyo and Washington remain deeply concerned about the broader trajectory in the regional balance of military power in Beijing’s favour and perceptions that it is increasingly willing to employ military tools to achieve its political ends. All three countries are thus pursuing the individual capabilities and the collective capacity to deny Beijing an easy military victory, attempting to make the costs of military action so prohibitive that China will actively choose not to resort to force in the first place. This approach is commonly referred to as ‘deterrence by denial’.
The concept of deterrence by denial and the geography of the First Island Chain are both central to the defence strategies of the three AJUS countries. The Trump administration’s 2025 National Security Strategy (NSS) and 2026 National Defense Strategy (NDS) are the most explicit, identifying deterrence by denial along the FIC as the chief organising construct for US military strategy in the Indo-Pacific.1 Successive Australian NDS documents have adopted a “Strategy of Denial as the cornerstone of Defence planning,” guiding capability investments and regional posture decisions in Australia’s “primary area(s) of military interest,” including the Southeast Asian components of the FIC.2 While less explicit, Japan’s own 2022 National Defense Strategy (scheduled to be updated in 2026) similarly identifies the FIC as the first point of contact with China’s expanding regional military footprint, reorienting the posture and reimagining the structure of the Japan Self-Defense Force to position and equip it for denial operations across the region, not simply in the defence of Japan.3
Yet it is the implementation of that strategic alignment that is the primary challenge for AJUS, as one of the contributors to this compendium notes. To that end, the three countries have already developed a robust roadmap for operationalising that alignment across information-sharing, defence industrial cooperation, integrated air and missile defence, air and maritime operations, and other areas. For these efforts to make credible contributions to collective deterrence, the three countries must grapple with a range of complex factors. This includes deciding on appropriate divisions of labour between the three countries in different operational contexts; reconciling differing political thresholds for the use of force; how national capability acquisition priorities and shortfalls may effect trilateral operational potential; agreeing upon levels of integration across command and control, industrial production, information sharing; and other factors. While progress is being made across all these metrics, much work remains to ensure that AJUS keeps pace with the growing challenges to deterrence and regional stability amid political and technological change.
In the spirit of advancing the trilateral defence agenda, the United States Studies Centre, with the support of the Australian Department of Defence, has brought together leading policy experts and practitioners from across Australia, Japan and the United States to identify the art of the possible across several areas for practical cooperation. Since mid-2024, the Centre has convened a series of five workshops featuring experts and officials from Australia, Japan and the United States who are focused on these areas and publishing corresponding reports that will highlight points of consensus or difference between the policy communities across all three countries on priority topics. The reports provide consolidated analyses of the opportunities for advancing cooperation in these areas. This compendium is the fifth and final in that series, featuring contributions from three leading experts from Australia, Japan and the United States, which collectively unpack the requirements of a trilateral denial strategy along the First Island Chain, and offer policy options for advancing the overall AJUS defence agenda.
Beyond alignment: An Australian perspective on operationalising Australia-Japan-United States defence cooperation along the First Island Chain
Jennifer Parker
Adjunct Professor, University of Western Australia Defence and Security Institute
Trilateral defence cooperation between Australia, Japan and the United States has made significant progress in the last decade. Strategic alignment on the challenges facing the Indo-Pacific is evident in their National Defence Strategies and a plethora of joint statements. The three countries broadly agree on the challenge posed by China and the need to strengthen regional deterrence. The task now is how to translate this strategic alignment into an effective operational deterrence strategy, and to understand what the key elements, roles and responsibilities of such a strategy would be. The US stated strategy of deterrence by denial along the First Island Chain (FIC) is one anchor point, but there are also broader considerations that must be considered.
Australia does not need to mirror the role of the United States or Japan. It needs to make the best use of its own comparative advantages, particularly its geography, strategic depth and capacity to sustain operations. Operationalising a trilateral deterrence strategy therefore depends on more than simply doing more together. It requires a clearer understanding of roles, better planning and greater integration in those areas that will make the greatest contribution to deterrence.
The logic of implementing a trilateral denial strategy
At the strategic level, the alignment between the United States, Japan and Australia is clear. All three countries have identified China as their primary strategic challenge and have issued strategic guidance that reflects an approach of deterrence by denial.4 Not only is there strategic alignment in how the three countries view China’s military modernisation and its use of military power in the region, but there is also increasing convergence, particularly between Australia and Japan, in how they assess broader regional dynamics. This was evident in the April 2026 Australia-Japan Defence Ministers’ Meeting Joint Statement that “reiterated our serious concerns” about the situation in the East China Sea and South China Sea and urged peace and stability around Taiwan, encouraging “dialogue rather than a resort to coercion or use of force.”5
On the latter, Australian Deputy Prime Minister Richard Marles put this clearly when he stated during his December 2025 visit to Tokyo that Australia has “never been more strategically aligned than we are with Japan today.”6 From an Australian perspective, Australia’s 2026 National Defence Strategy (NDS) prioritises both trilateral and bilateral cooperation, recognising that stronger bilateral relationships are often an enabler for trilateral cooperation.7 The 2026 NDS makes clear that Australia intends to deepen trilateral defence cooperation with the United States and Japan, with a focus on improving interoperability, strengthening deterrence, and expanding practical cooperation through exercises, operations, technology and capability initiatives.8 Much of this trilateral cooperation is already apparent through Exercises Talisman Sabre, Keen Edge and Keen Sword.
On bilateral cooperation, Australia’s NDS states that “Japan is an indispensable partner for achieving regional peace and prosperity” and notes the “growing interoperability, including in a trilateral context with the United States.” Highlighting that Australia will increase information sharing with Japan and significantly “deepen discussions on current and future deterrence activities — such as Flexible Deterrent Options — which demonstrate capability and resolve.”
On the US bilateral relationship, it is even more ambitious, stating that the alliance is “fundamental” to Australia’s national security and that “it is critical to maintaining collective deterrence and regional stability in the Indo-Pacific.”9 US force posture initiatives and the Australia-Japan Reciprocal Access Agreement, which has enabled more frequent and sophisticated exercises and operational visits in both countries, have further strengthened trilateral cooperation by enabling more regular exercises, operations and access arrangements among the three partners. It is clear that the objective is to translate strategic alignment into operational integration.
The logic of trilateral deterrence is straightforward. No one country can execute a denial strategy alone. From an Australian perspective, effective deterrence rests on the complementarity of the three partners: US scale and integration, Japan’s forward posture, and Australia’s geographic depth and rear-area sustainment potential.
Challenges in trilateral cooperation
There are several barriers to cooperation that require a concerted effort amongst the three partners to deliver a coordinated deterrence strategy. The first, and perhaps most challenging issue, is how the trilateral strategy is conceived and implemented. While this may appear straightforward, it will be challenging and require a concerted effort.
The US National Security Strategy emphasises the United States’ intent to enact a “strong denial defence along the First Island Chain (FIC).”10 At first glance, this makes sense: denying China’s ability to operate effectively beyond the FIC. A strategy that has been further strengthened by technological advances, including drones and artificial intelligence-enabled intelligence, surveillance and reconnaissance (ISR). The wars in Ukraine and the Middle East have demonstrated how these technologies have significantly enhanced the effectiveness of geographic maritime denial strategies.
The limits of a First Island Chain strategy
The main challenge of a trilateral denial strategy is that it is clear China’s military capabilities extend beyond the FIC.
Its transition to a power projection strategy has borne fruit. Chinese naval assets now deploy regularly beyond the FIC, as demonstrated by the circumnavigation of Australia by a Chinese naval task group in February–March 2025,11 and a subsequent deployment to the Pacific that came within five nautical miles of Australia’s exclusive economic zone in December 2025.12 China’s extensive survey operations across the Indian Ocean are likely a precursor to more frequent submarine operations in the region.13 This does not preclude deterrence by denial as the unifying concept for a trilateral strategy. However, the limitations of such an approach must be understood when assessing the role each nation can play in enabling and sustaining that strategy.
Roles and responsibilities
For Australia, the implication is that its defence capability is best focused on protecting Australia and exploiting the strategic depth afforded by its geography. Australia’s primary role, both from a national and trilateral context, is to defend the continent and ensure the continued flow of the critical seaborne supplies that would allow Australia to sustain itself and provide the depth required to support operations along the FIC.
In short, the greatest challenge from an Australian perspective will be maintaining alignment around the fact that, while deterrence by denial along the FIC may serve as the unifying strategy, the Australian Defence Force’s principal role is the defence of Australia, to provide strategic depth to a FIC strategy. Beyond this, Australia would likely only have limited capacity to deploy bespoke contributions such as special forces, intelligence, surveillance and reconnaissance assets, uncrewed underwater vehicles or submarines to operate in or around the FIC. Australia’s focus would be supporting operations beyond the FIC and undertaking tasks across the Pacific and Indian Oceans to secure the seaborne supply lines on which Australia depends.
Political challenges
Once roles and responsibilities are understood and delineated, the next challenge is political. Australia, the United States and Japan each have different political dynamics, domestic pressures and thresholds for committing military capability. In Australia, this is evident in the debate surrounding AUKUS Pillar I and the acquisition of nuclear-powered submarines. While Lowy polling since 2022 has consistently shown majority support,14 opposition remains vocal. Much of this debate is not about the submarine capability itself but broader concerns about alliance management and Australia’s strategic autonomy. These debates are further complicated by Australia’s trade relationship with China and sensitivities around how military strategies aimed at deterring China are perceived domestically in Australia.15
These challenges are not prohibitive, but they demonstrate how each country will face its own domestic political pressures that will influence both its messaging around a trilateral deterrence strategy and its threshold for action. This is particularly relevant where coordinated responses may require the use of all elements of national power to respond to competition below the threshold of conflict. For example, Australia’s willingness to employ economic measures as part of its response toolkit may differ from that of its partners, particularly given the significance of trade with China to Australia’s economy. This dynamic was evident in the United States Studies Centre’s 2025 war game, which noted “economic sanctions were difficult to coordinate trilaterally, given, in particular, Australia’s exposure to the PRC export market.”16
Capability and capacity pressures
Military capability and capacity pressures, particularly in Australia and the United States, pose a real limitation to implementation of a trilateral denial strategy. Both Australia and the United States maritime capabilities are suffering from a lack of investment from the end of the Cold War through to the 2000s, and arguably even now. For Australia, this has created force structure pressures in the number of deployable ships and submarines that will persist until new surface combatants and submarines enter service in the 2030s. Until then, ageing platforms will continue to constrain force availability.
The United States is also facing significant force structure challenges this decade; a period the American Enterprise Institute labelled the “Terrible Twenties” in 2021.17 The report noted that 28 modernisation programs were cancelled between FY2002 and FY2012 as funding was redirected to support the Global War on Terror. The effects are now being felt in operational availability and will continue to shape US force readiness for some time. This is evident in persistent ship maintenance delays and the poor condition of parts of the fleet. In 2024, for example, 16 of the US Navy’s 32 amphibious warfare ships were assessed as being in an unsatisfactory condition.18
Exacerbating this challenge is the United States’ global force commitments, as demonstrated by the diversion of military assets from the Indo-Pacific to the Middle East in support of operations against Iran beginning in 2026.19 While force availability will remain an unavoidable challenge for both Australia and the United States over the next decade, it must be factored into efforts to operationalise a trilateral deterrence strategy. This will require prioritising high-impact activities, including exercises and operations, rather than simply increasing the number of engagements, which is often the default response to new initiatives. It will also require designing cooperative activities that acknowledge capability constraints and account for them from the outset.
While role clarity, political dynamics, and Australian and US capability constraints will be important challenges that must be factored into operationalising a trilateral deterrence strategy, they are not the only barriers. There remains no clear understanding of who would do what in a regional contingency, or how responsibilities would evolve as a crisis developed. There is also a persistent gap between the concept of trilateral deterrence and its execution. For example, while the idea of trilateral deterrence may be generally supported, how this would work in practice beyond military deterrence initiatives is unclear. Cooperation has advanced significantly through policy initiatives, exercises and strategic dialogue, but less so in integrated operational planning.
In many respects, trilateral cooperation still resembles a series of connected bilateral relationships rather than a genuinely integrated trilateral framework. Australia increasingly participates in US–Japan activities such as exercises Keen Edge and Keen Sword,20 but participation does not necessarily equate to integrated command and control, targeting processes or decision-making. If the trilateral partnership is to deliver a credible deterrence capability, it must increasingly focus on operational integration rather than cooperation alone.
In many respects, trilateral cooperation still resembles a series of connected bilateral relationships rather than a genuinely integrated trilateral framework.
The present state and future requirements of such cooperation
The question is not whether there is strategic alignment between Australia, Japan and the United States, nor whether a trilateral approach to regional deterrence is important. Both are clear, notwithstanding the challenges outlined above. The real question is how that strategic alignment is translated into an operational capability that enhances deterrence. In that respect, there has already been significant progress, reflected in the current state of trilateral cooperation.
The growing number of minilateral and multilateral exercises involving Australia, Japan and the United States demonstrates a clear focus on improving interoperability.21 While this has enhanced cooperation between the three countries, interoperability should not be conflated with integration. Integration will be essential to bridging the gap between a trilateral concept and the ability to operationalise the concept. Importantly, integration does not mean the full integration of Australian, Japanese and US military forces. Discussions of integration often default to concepts of interchangeable forces operating under a common command arrangement. While some have advocated for that model,22 it is not what is being proposed here. Any trilateral framework must preserve national decision-making and strategic autonomy.
So, what does integration actually look like? There are several key elements. First, there must be agreement at the government level on the tools available to support broader deterrence initiatives and the circumstances in which they may be employed. This extends beyond military power and includes the diplomatic, economic and informational levers available to each nation. Just as importantly, there must be a shared understanding of the political thresholds, constraints and barriers that may influence their use. Developing that understanding is unlikely to require a leaders’ meeting, but it will require sustained engagement through official and unofficial dialogues, including Track 1 (official only) and 1.5 (officials and experts) processes. Once established, those discussions should expand to include key regional partners where appropriate. Effective deterrence in the Indo-Pacific, but also along the FIC, will ultimately require a broader network of aligned partners, not simply trilateral coordination. This must also be supported by trilateral agreement on how the three countries would respond to regional contingencies, whether around Japan, Australia, the South China Sea or elsewhere in the Indo-Pacific.
The next element is a clear military division of responsibilities, based on both geography and function. This moves beyond cooperation to integration, not through interchangeable forces, but through integrated planning. This ensures all three countries understand the role each would play in a contingency. This will improve coordination and response times in a crisis.
The third element is addressing command and control in a trilateral fashion. This does not require a standing trilateral headquarters or the surrender of national command authority. Instead, it requires arrangements that allow Australia, Japan and the United States to rapidly share information and synchronise operations during a crisis. There has already been progress in this area. The establishment of the Japan Joint Operations Command (JJOC) in 2025,23 reciprocal liaison officer arrangements between JJOC and Australia’s Headquarters Joint Operations Command, and the creation of the Trilateral Defence Consultations mechanism have created some initial practical foundations.24 These foundations would be enhanced by more regular trilateral planning and exercising between existing headquarters.
The fourth element is targeting and information integration. While intelligence sharing and trilateral ISR cooperation have expanded significantly in recent years, including through Australia’s participation in the Japan-US Bilateral Information Analysis Cell,25 the next step is ensuring that shared information can support coordinated operational outcomes. In a military context, an effective denial strategy relies on the ability to rapidly detect, track and respond to military activity across the Western Pacific. Sharing information is important, but it is only one step. The three countries will increasingly need common processes that enable information to support coordinated decision-making and targeting. Existing trilateral cooperation on an “air and missile defence data sharing framework” among the three countries is a positive step.26
The final focus piece is sustainment. Recent initiatives such as the trilateral naval logistics arrangement are welcome,27 but they should be viewed as a foundation rather than an end state. Exercises are generally good at testing combat capability, but less effective at testing whether that capability can be sustained over time. For a deterrence strategy built around persistence, sustainment matters. Future activities should place greater emphasis on fuel, munitions, maintenance and the ability to continue operating when bases, ports and supply chains are under pressure. From an Australian perspective, this is particularly important. Australia’s greatest contribution to a trilateral deterrence strategy is unlikely to be providing operational mass or forward presence, but rather in the strategic depth and collective sustainment capacity that it can provide to its partners.
The issue is not whether Australia, Japan and the United States are strategically aligned. They clearly are. An effective trilateral deterrence strategy will require turning that alignment into practical military outcomes. Considerable progress has already been made, but there remains an important difference between cooperation and integration.
For a deterrence strategy built around persistence, sustainment matters.
A trilateral strategy for denial defence of the First Island Chain: A Japanese perspective
Professor Satoru Mori
Professor of Contemporary International Politics, Keio University, Deputy Director, Keio Center for Strategy (KCS)
This contribution addresses three issues: a) the logic of implementing a trilateral denial strategy; b) the requirements of cooperation; and c) the challenges to such cooperation. Defence industrial resilience is a major area of cooperation, and there is a large set of policy issues on that theme, but this essay will focus mostly on issues related to strategy, operational cooperation, force posture and capabilities required for denial defence of the First Island Chain (FIC).
The logic of a trilateral denial strategy
What is the strategic objective of Australia, Japan and the United States (AJUS or ‘the trilateral’ hereafter) and what is the strategy to achieve that objective? The trilateral shares the common strategic objective of preventing the establishment of a regional hegemony through coercion and force, and they are aligned in terms of strengthening deterrence vis-à-vis China. The most recent US National Defense Strategy’s denial defence28 and Australia’s National Defence Strategy’s collective deterrence overlap,29 and it is likely that the Japanese National Defense Strategy, due in 2026, would also align in this regard.
Trilateral defence cooperation designed to exercise deterrence by denial needs to be designed to send signals that will generate four kinds of strategic effect on the Chinese leadership’s politico-military decisions. These effects specifically need to convince Beijing that:
- It cannot win a short-sharp war.
- It cannot previal in a protracted conflict.
- Its multifaceted coercion campaigns against Taiwan and regional states will not help change the status quo but only strengthen resistance.
- Japan, Australia and the United States are capable of effectively converting national economic power into warfighting capabilities over a sustained period through defence industrial base cooperation.
Sending the above signals will require a regional deterrence architecture with several layers of geopolitical stakeholders. The different roles played by regional and extra-regional states could be characterised as follows. The frontline states are Taiwan, Japan and the Philippines. The primary security provider is the United States, and the secondary security provider is Australia. These countries notionally constitute the ‘inner ring’ of regional deterrence. There are also tertiary security providers — Southeast Asian states and certain European states — that would be gravely affected by an armed conflict in the Western Pacific and would want to avoid an eruption of armed conflict; they constitute the ‘outer ring’ partners for regional deterrence.
The players in the inner ring need to enhance mutual defence cooperation by articulating and harmonising concepts of operations, connecting Command and Control (C2) architectures, establishing a viable force posture and jointly developing capabilities that will all serve to achieve deterrence by denial. A trilateral denial strategy would indeed be the critical hinge for the inner ring, along with a SQUAD — the United States, Japan, Australia and the Philippines — denial strategy. There should be a sustained and coordinated effort by the trilateral to bolster Filipino defence capabilities and national resilience, since the more vulnerable it is, the more challenging FIC denial defence becomes.30
The inner-ring players also need to engage the outer-ring partners to systematically develop security cooperation. There is a history of advancing cooperation on maritime security and maritime domain awareness (MDA) with Southeast Asian nations because it has direct implications for the security of the FIC.31 Certain European states would probably want to cooperate in the realms of intelligence sharing, space, cyber and information operations, and the inner-ring states should continue to advance cooperation in those areas as well. At the end of the day, there should be a conscious effort among the inner- and outer-ring partners to connect sensor networks across multiple domains and aggregate data on situational awareness.
Ultimately, a trilateral denial strategy should be nested within a multi-layered regional defence architecture designed to generate the four strategic effects defined above. A trilateral denial strategy is not the sole source of regional deterrence, yet it forms a critical part of a web of defence and security cooperation aimed at deterring China.
Requirements for inner ring cooperation
In what ways should the trilateral cooperate to bolster deterrence? Political, military and fiscal circumstances of individual states will limit their respective scope of cooperation, but to credibly deter China, inner ring states should ideally cooperate across nine potential areas for inner ring defence.
- These nine areas are not exhaustive, and not all efforts are possible among all the relevant states, but they could be considered to constitute requirements of denial operations for the defence of the FIC. The trilateral is already cooperating on regional training and exercises, increasing Japan’s participation in Australia–US force posture activities, aligning strategic communications, and discussing effective cooperation through initiatives such as tabletop exercises regarding responses to regional contingencies, among others. Japan–Australia bilateral cooperation is helping to advance more effective trilateral cooperation. Elements of cooperation are listed where appropriate to provide a very brief notional description of what it would entail, but they are not exhaustive.
Potential areas for inner-ring defence cooperation:
1. Enhancing combined IAMD architectures.
- Ballistic missile defence (BMD) data-sharing
2. Cooperating and providing mutual support on contested logistics and transport.
- Reciprocal Access Agreement (RAA)
- Acquisition and Cross-Servicing Agreement (ACSA)
- Strategic transport coordination and cooperation
3. Coordinating operational anti-ship and ASW missions among countries with the necessary capabilities.
- Exercises Trident and Pacific Bond
- ASW platform procurement
4. Coordinating operations regarding conventional strike and offensive cybver operations.
- Modernisation of command and control for All Domain Operations
- Closer C2 coordination
5. Establishing hardware (including munitions and vital military materiel) interoperability and standardisation and co-production to enable and facilitate cross-national sustainment capacity.
- Co-production of missiles and munitions
- Missiles and munitions stockpiling and standardisation
6. Providing capacity-building and sharing best practices for achieving high resilience in cyber and critical infrastructure and networks.
- Cyber framework for cooperation
- Quad critical infrastructure protection
7. Sharing best practices regarding civil defence measures.
8. Consulting on options for potential economic and financial sanctions as well as reinforced export control measures.
- Counter-economic coercion initiatives
- Export control coordination
9. Consulting on diplomatic and information operations including strategic communication with other non-AJUS countries, including those in the Global South.
- Counter-information operation initiatives
- Strategic dialogues
Operational cooperation: Requirements and challenges
Modernising command and control and establishing close trilateral coordination is a key requirement to operational cooperation. A modern denial operation will require the ability to have a common operating picture (COP) and flexibly and efficiently strike targets in a timely and coordinated manner. If the goal is to gain the ability to implement an effective denial operation against the PLA, constructing what could be called a ‘Denial Web’ is a necessity. It would be the kind of battle management system necessary to cope with a region-wide PLA ‘intelligentised’ operation. For example, a Japanese destroyer or an Australian F-35 could provide targeting data for a US Army Typhon system deployed in the Philippines.
The challenge is that this is a very high bar. The trilateral will need to advance all domain data sharing despite the fact that information security and information-sharing baselines among the three countries differ. Also, while all three militaries deploy standard protocols like the Link 16 military data network, the sheer volume, speed and algorithmic complexity needed to defeat an intelligentised PLA attack are likely to exceed existing baseline capabilities. The US military’s internal concept — Combined Joint All-Domain Command and Control (CJADC2)32 — is built upon highly classified, proprietary data architectures and artificial intelligence blocks. Transitioning this framework from a US national capability into a trilateral tool will be a daunting challenge.
Nevertheless, the trilateral BMD/IAMD cooperation initiative is spearheading the initiative of deepening trilateral operational cooperation.33 It is transitioning from a loose collection of bilateral pathways into a highly networked operational architecture. The three nations are actively pursuing what they term the TRISHIP (Trilateral Air/Surface/Missile Information Sharing in the Indo-Pacific).34 Rather than developing a singular, trilateral hardware unit, the initiative focuses on stitching their sovereign sensor and command platforms together to form a highly resilient, regional interception net. This initiative will help the trilateral identify barriers and tasks to develop coalitional data-centric warfare capability.
Force posture: Requirements and challenges
With regard to force posture, Distributed Maritime Operations — spreading out naval assets across a wider area to make adversarial targeting more difficult — has been called for by the US Navy and it has been pointed out that mobility and dispersion are crucial.35 The three countries must increase the number of accessible bases and expeditionary airfields across the Indo-Pacific through the Agile Combat Employment (ACE) concept,36 and that should ideally pursue a ‘plug-and-play’ infrastructure where Australian, US and Japanese units can share fuel, munitions and maintenance facilities seamlessly. However, the asymmetry in strategic depth between China on the one hand and Japan, Taiwan and the Philippines on the other is significant. This is further complicated by the fact that the threat of PLA’s theatre-range offensive capabilities is steadily increasing.37 One of the solutions to this problem is enhancing resilience, but it is unclear whether the inner ring states have enough capacity for repair, replenishment, stockpile and production, and whether they can establish viable contested logistics in the theatre. Thus, a collective metric to measure resilience is needed to clarify specific shortfalls and prioritise new investments.
Capabilities: Requirements and challenges
Regarding capabilities, there is ongoing cooperation for the upgraded Mogami-class frigate,38 the Ghost Bat Collaborative Combat Aircraft (CCA),39 Maritime Big Play (unmanned underwater vehicle (UUV) networked communications),40 and joint research and development for composite materials for high-speed aircraft and missiles.41
A critical capability requirement in an FIC denial operation is undersea denial, given China’s growing manned and autonomous undersea capabilities. There might be an opportunity to advance trilateral cooperation with the Philippines on expanding and enhancing the Integrated Undersea Surveillance System (IUSS) that would capitalise on the combined use of UUVs and Fixed Distributed Systems, battery-powered sensor nets scattered across the seabed.42 Maintaining advantage in the undersea competition would require exploiting a host of capabilities and advanced sensor and communication technologies; there is a case to be made for tackling this requirement through a trilateral approach.
Ramping up missile production is another major requirement. Though efforts are already underway in the United States to greatly expand missile production capabilities,43 it will reportedly take one to five years to replenish stockpiles of missiles to pre-Iran operation levels, depending on the missile type.44 Encouragingly, the AJUS countries are exploring additional cooperation on missile production. Following high-level summits, the United States and Japan agreed to radically increase Japanese domestic production lines for the SM-3 Block IIA interceptor by fourfold.45 This push ensures a stable supply of high-altitude ballistic missile interceptors for both US INDOPACOM and Japan's upcoming Aegis System Equipped Vessels (ASEVs). Through its Guided Weapons and Explosive Ordnance (GWEO) Enterprise,46 Australia is scaling up domestic defence manufacturing plants (such as its major facility in Port Wakefield).47 This enables Australia to serve as a secure supply hub for missile subcomponents and solid rocket motors, easing the burden on heavily strained US industrial capacity.
Conclusion
There is a need to undertake a broad-net assessment to identify asymmetries between China, Russia and North Korea on the one hand, and the United States, Australia, Japan, Taiwan and the Philippines on the other. It is necessary to address the question of what the trilateral’s asymmetric advantage over China and its partners would be in five to ten years from now. There is an emphasis on the trend to shift to mass, low-cost, autonomy and decision-centric warfighting, which is sound and necessary, but China is developing the same kind of capabilities. It is necessary to inquire whether the trilateral is truly exploiting China’s weakness by leveraging its own strengths.
Furthermore, it is also necessary to examine war termination strategies. If deterrence fails and decisions are made to conduct denial operations by the United States and its allied governments, it is possible that a conflict would become protracted. The three countries will face varying circumstances and yet will need to agree on a common strategic objective and also decide who will play what role and carry out which missions. Maintaining political solidarity and agreeing on operational priorities during a protracted conflict will be the true challenge of a denial strategy for the defence of the FIC.
The promise and the challenges of trilateral security cooperation between Australia, Japan and the United States
Jeffrey W. Hornung
Adjunct Professor, Edmund A. Walsh School of Foreign Service, Georgetown University
As the regional security environment grows increasingly complex — shaped by shifting power dynamics, evolving technological threats and challenges to the rules-based international order — the collaboration among the United States, Japan and Australia has never been more crucial. Termed ‘the inner core’ of regional order building and deterrence within the US-led alliance network, these countries can leverage trilateral security cooperation for the benefit of the Indo-Pacific region.48 By deepening security collaboration, these three countries are well equipped to deliver more cohesive and effective responses to Indo-Pacific challenges.
Should a conflict over Taiwan occur, it is assumed that China will seek to leverage freedom of movement or access — especially to sea lines of communication, forward bases and air/maritime manoeuvre space — in or beyond the First Island Chain (FIC). Because it is in the interests of all three countries to prevent China from achieving this, it is important to consider ways they can work trilaterally to prevent this. This essay analyses which types of trilateral security cooperation would likely be required in both peacetime and a contingency to prevent China from achieving freedom of movement or access in or beyond the FIC. It then touches on some possible challenges to meet these requirements, before closing with some thoughts on possible ways to overcome these challenges
Peacetime requirements
In peacetime, trilateral denial operations are about shaping Chinese behaviour. There are many areas where the three countries could cooperate to do so, but in the defence domain there are three likely requirements that could be the most beneficial toward this end: domain awareness, infrastructure and sustainment resilience and force integration training.
The first is domain awareness. China’s modernisation of its military capabilities, including advanced missile systems, cyber capabilities and grey-zone tactics in contested areas, makes it essential for the United States, Japan and Australia to maintain real-time awareness.49 China’s increasingly assertive actions, such as deploying coast guard and maritime militia to assert territorial claims, heighten the risk of incidents at sea.50 Domain awareness provides crucial situational understanding to defend territorial waters, uphold freedom of navigation and ensure adherence to international law. For the three countries to do this cooperatively in an effective manner, they will need to use their air and maritime assets to provide continuous intelligence, surveillance and reconnaissance (ISR) across key maritime chokepoints, such as the Luzon Strait, East China Sea and Bashi Channel.
Resilience, however, cannot be surged in a conflict.
The second is infrastructure and sustainment resilience. China’s military modernisation includes capabilities to target supply chains, bases, communications networks and logistical hubs — often through cyberattacks, missile strikes or other forms of hybrid warfare.51 Resilient infrastructure ensures that critical facilities can withstand, recover from and adapt to these disruptions. Resilience, however, cannot be surged in a conflict. Once a conflict begins, effective security operations will rely on sustained access to fuel, supplies, transportation networks and communications. For the three countries to best prepare for that possibility, they will need to act in peacetime. Things the three countries could consider include ‘hardening’bases and ports in Japan and Guam, including fuel and ammunition storage in northern Australia and Western Japan for dispersed coalition operations, and creating dispersed logistical nodes in northern Australia to support sustained operations if access east of the FIC is contested.
The final requirement is force integration training. Each country’s armed forces operate with distinct systems, procedures and protocols. Force integration training can help bridge these differences, ensuring that personnel, equipment and processes can work together. In peacetime, these types of activities send a strong signal of resolve and capability to would-be aggressors. Gaining any improvements in interoperability will be essential for effectively responding to crises. Already, these three countries exercise extensively together. Through exercises like Malabar, Talisman Sabre, Cope North, Pacific Vanguard, and various command post and humanitarian aid and disaster relief (HA/DR) drills, the United States, Japan and Australia continually train toward force integration.52 The more these types of exercises occur, the morethey can help create operational habits before a crisis erupts. Because the means of warfare is changing, the three countries could benefit from focusing on routine, small-unit exercises that emphasise distributed lethality, unmanned teaming and cross-domain joint fires.
Contingency requirements
In a contingency, trilateral efforts would need to shift from shaping Chinese behaviour to defeating Chinese operations. In this situation, the forces would have multiple competing requirements. Below are four that have the potential to be the most important.
The first is surface and subsurface denial operations. China is rapidly expanding and modernising both its surface navy and its fleet of submarines.53 Surface and subsurface denial operations, such as anti-ship and anti-submarine warfare, make it harder for China to project its military power beyond its shores.54 By possessing strong denial capabilities, the three countries can limit China’s operational choices in a crisis, constraining its ability to escalate militarily. Because of the strength of their combined fleets, US nuclear submarines, Australian conventional submarines (and eventually nuclear-powered) and Japan’s Sōryū- and Taigei-class submarines could form a combined picket line to stop People’s Liberation Army Navy (PLAN) advancements out of the FIC.55 These same assets could be used to hunt Chinese surface action groups that operate in the East China Sea and out to the Western Pacific. Because PLAN assets would have to transit through a small number of chokepoints in the East China Sea to advance into the Pacific Ocean, such as the Miyako or Ōsumi Straits, these denial operations would likely require cooperation on mine warfare as well.56
The second requirement is air and missile denial operations. China has developed a sophisticated array of air and missile assets, including long-range ballistic and cruise missiles, advanced fighter aircraft and bombers.57 These weapons can threaten bases, ships, airfields and other infrastructure across the Indo-Pacific. Denial operations — such as integrated air defence, anti-missile systems and active air patrols — are means by which to help neutralise or mitigate these threats. For the three countries to meet this challenge, they could benefit from coordinating distributed air defence using the US Terminal High Altitude Area Defense (THAAD) on Guam, Japanese and US Aegis destroyers, and U.S. and Japanese Patriots and other surface-to-air missiles (SAMs) to create overlapping coverage in Northeast Asia and the Western Pacific. For disabling China’s air threats, the three countries would likely need to rely on long-range precision fires from airborne assets based on the US mainland or Australia but could also benefit from Japanese stand-off missile batteries to deny more localised movement in the East China Sea.
The third requirement is cyber and electronic warfare denial operations. China has invested heavily in cyber tools and electronic warfare systems that can disrupt communications, degrade command and control, manipulate information and target critical infrastructure in all of the three allies’ countries.58 Because China is likely to lead with these efforts in a crisis, denial operations will be necessary to protect allied networks, maintain operational security, and shield sensitive systems from intrusion, sabotage or exploitation.59 To meet this requirement, the three countries could continue work to further align the defence of their individual networks and coordinate offensive electronic and cyber efforts to cut Chinese command networks without risking potential vertical escalation. They could also perform integrated electromagnetic spectrum operations from ground and airborne platforms to disrupt Chinese forces operating in theatre.
A final requirement to defeat Chinese operations is sustainment and forward repair operations. All the military capabilities being developed by China have the potential to target supply lines, bases and critical logistics networks in the region.60 Sustainment operations guarantee that units can remain supplied with fuel, weapons, spare parts and other necessities, even in contested environments. Similarly, forward repair operations enable damaged equipment to be quickly restored close to the fight, rather than withdrawn to distant bases. Should the three countries achieve the second requirement of air and missile defence operations, sustained operations are likely to be unproblematic. Depending on the scale of the conflict, however, they may need to consider other ways to achieve this. Because of its distance from the theatre, Australian territory could serve as a critical rear logistics hub for US forces to take pressure off bases in Guam and Hawaii, something that is already materialising.61 Should the fight escalate to the point where even Guam is contested, Australia may also act as a sanctuary for US forces. To support the forces in theatre, Guam and Japan could act as forward sustainment and casualty evacuation points for not just US forces, but all coalition partners. Should Japan come under repeated assault making US operations from Japan unsustainable, Guam and Australia could act as dispersal points for Agile Combat Employment plans.
Challenges
None of this will be easy, as there are challenges the United States, Japan and Australia may encounter as they seek to conduct effective trilateral denial operations. Although many challenges could be considered, this essay highlights three broad categories that could shape how far the three countries are able to advance their cooperation.
The first category involves political and legal considerations. Within the framework of Washington’s individual alliances with Tokyo and Canberra, the United States generally faces few political or legal obstacles that would prevent it from pursuing any of the requirements bilaterally or trilaterally. However, both Japan and Australia may encounter challenges that could impact the depth of their cooperation. While the Japan Self-Defense Forces (JSDF) have made significant strides in improved capabilities and expanded defence policies, they continue to operate under constrained legal parameters.62 The focus on self-defence, for example, means higher hurdles to use force and when Japan can exercise collective self-defence measures; it also sets conditions for US access to bases for combat operations not directly tied to Japan’s defence — particularly for kinetic operations launched from Japanese territory when Japan is not under direct attack.63 As a result, there may be limitations on Japan’s ability to take on some of the requirements or participate in certain trilateral operations unless there is a direct threat to its own security. For Australia, strong support for US operations remains a hallmark of the alliance and is not generally seen as problematic. However, there may be questions in Canberra regarding the extent to which Australia would be willing to undertake denial operations far from its home territory if not directly tied to Australia’s defence, such as Japan.
The second category of challenges relates to interoperability and command structures.64 While robust bilateral mechanisms exist between the United States and Japan, and between the United States and Australia, direct connections between Japan and Australia are still evolving.65 To date, exercises have done much to foster basic interoperability among the JSDF, the Australian Defence Force (ADF) and US forces.66 Nevertheless, further progress may be needed in areas such as technical standards, command-and-control arrangements, communications security and intelligence sharing — particularly at the operational and tactical levels essential for denial operations, such as integrated missile defence, anti-submarine warfare and counter-air activities. Trilateral command and control can be especially complex, given sovereignty considerations and the limitations inherent in multilateral planning.
The final category is intelligence and information sharing. The United States and Australia enjoy a strong tradition of sharing classified information thanks to their longstanding Five Eyes partnership. While the United States and Japan have made significant progress in this area, some US concerns remain regarding Japanese information security practices.67 Additionally, despite some progress, Japan and Australia have not yet developed the same depth of intelligence-sharing that exists between Australia and the United States.68 Building trust and secure information-sharing mechanisms takes time and sustained effort, especially at the highest levels of classification.69 These do not exist today. If challenges in sharing critical intelligence persist during operations — such as real-time targeting data — it could impact the effectiveness and speed of trilateral cooperation. In such cases, coordination might be limited to operational ‘zones’ rather than all three forces functioning as one team.
Looking ahead
This final section presents potential approaches to address these challenges. These are organised by levels of effort, gradually increasing in complexity as the United States, Japan and Australia deepen their integration.
Low-end: Cooperation and deconfliction
At a minimum level — where the countries are already making great strides — the United States, Japan and Australia can continue to benefit from deepening their understanding of how their armed forces cooperate across different scenarios. By focusing on ways to deconflict operations and align activities with each nation’s political and legal sensitivities, greater clarity and confidence in trilateral efforts can be achieved. Expanding joint training and exercises is one way to foster this cooperation. Regular, large-scale trilateral exercises in and around the FIC and Western Pacific could provide opportunities to rehearse key mission areas such as anti-access/area denial, anti-submarine warfare, integrated air and missile defence and strike operations.70 While these exercises are unlikely to achieve full operational integration, their purpose would be to promote a better mutual understanding of each force’s tactics, techniques and procedures (TTPs) as well as their respective rules of engagement (ROEs). They would also help develop robust deconfliction protocols such as WaterSpace Management. a naval command and control process used to coordinate subsurface, surface, and air movements to prevent collisions between friendly assets.71 Additionally, since successful denial operations depend on secure access to bases, logistics hubs and repair facilities, these training opportunities could include the rehearsal of shared access agreements. Doing so could support the development of coordinated courses of action (COA), enabling rapid movement of forces and streamlined access to each other’s bases for staging, refuelling and repair.
Mid-level: Coordination
If the United States, Japan and Australia are committed to effectively denying Chinese operations, it likely will eventually become important for them to develop coordinated trilateral operational plans for contingencies within the FIC — encompassing rapid reinforcement, area denial and counter-landing operations. To operate efficiently as distinct yet mutually supportive partners, greater alignment in key areas would be beneficial. For example, developing harmonised rules of engagement (ROEs), comparable tactics, techniques and procedures (TTPs) and shared frameworks for escalation management would greatly enhance their ability to act quickly and more cohesively in a crisis. This might involve establishing agreed thresholds for triggering certain kinds of coordinated denial actions.
Continuous and integrated ISR is another area where the three countries may benefit their collective effectiveness. This is already beginning to happen, as witnessed in the aforementioned exercises. Enhancing intelligence sharing and integrating sensor networks — such as satellites, maritime patrol aircraft, submarines and over-the-horizon radars — could provide a comprehensive, real-time picture of the operational environment. Achieving this would also likely require secure, redundant communications through advanced satellite constellations and robust data-sharing protocols.
Lastly, leveraging improved infrastructure and logistics resiliency to support operations could require deeper coordination. The United States can expand its forward-deployed assets in Japan and increase rotational deployments in Australia, while Japan and Australia could pursue routine deployments on each other's territory. Deploying interoperable missile defence and anti-ship missile systems — especially on strategic locations such as the Nansei Shotō (the Ryukyu Islands), Guam and northern Australia — would further strengthen the ability of the three countries to coordinate and sustain joint operations.
High-end: Integration of effort, not command authorities
The most efficient approach to trilateral operations would be fully integrated command structures; however, sovereignty concerns make this unlikely. An effective alternative may be to pursue integration of operations — rather than command authority — which could enable the three countries to execute distributed, multi-domain denial operations through integrated ISR capabilities, long-range precision strike and undersea superiority.
To reach this advanced level of trilateralism, the three nations could focus on two key areas. The first is enhanced interoperability. Building on the previous step, the partners could advance toward integration by developing and adopting shared doctrines, ROEs and operational concepts tailored specifically to scenarios in the FIC. Progress in communications integration will likely also be vital, including robust communications and datalink systems across assets. This could involve cross-certification of encryption and communication protocols, enabling seamless information flow and real-time operational coordination.
An effective alternative may be to pursue integration of operations — rather than command authority.
The second key area is closer operational command integration, without merging command authorities. By establishing a trilateral standing operational coordination centre with planning capabilities, the three countries can conduct coalition mission planning while maintaining sovereign control over their forces. This centre could facilitate the creation of trilateral protocols for cyber defence as well as space-based communications and surveillance. Furthermore, the establishment of a trilateral fusion centre with real-time intelligence capabilities could provide a common battlespace picture, allowing coalition partners to effectively task their respective assets to targets in a coordinated manner. The development of a coalition target list could further streamline assignments, ensuring efficient use of sovereign resources and maximising collective impact.
Conclusion
By carefully addressing the requirements to counter Chinese operations in and beyond the First Island Chain, thoughtfully managing political and legal considerations, and enhancing interoperability and operational coordination, the United States, Japan and Australia can significantly strengthen their trilateral security partnership. Building on their existing relationships and pursuing practical, incremental steps, these three countries are well equipped to deliver more cohesive and effective responses to Indo-Pacific challenges. In doing so, they can reinforce their collective capacity to uphold regional peace and stability.
Conclusions and recommendations
Tom Corben
Research Fellow, Foreign Policy and Defence, United States Studies Centre
The three expert contributions and trilateral Track 1.5 workshop conducted in support of this publication suggest that policy practitioners in Australia, Japan and the United States are generally well-aligned when it comes to the benefits and requirements of a trilateral denial strategy in the region, including along the FIC. Even so, there is evidently much work for all three countries to do to operationalise and to harmonise their approaches to implementing that strategy. The five findings below capture the main contours of the three papers included in this report and the workshop discussions, as well as other areas for consideration and further investigation.
1. The First Island Chain might be a useful construct for geographically bounding a trilateral deterrence strategy within the region, but would be highly unlikely to contain a high-end conflict should deterrence fail. This raises questions about whether the FIC alone is the appropriate unifying construct for trilateral defence cooperation. It is true that China’s maritime territorial disputes with its neighbours and its claims over Taiwan all fall along the FIC, and that deterring and denying Beijing’s ability to seize these features by force should be a paramount concern for AJUS. Yet should deterrence fail, it is highly unlikely that fighting would remain localised to that geography, especially in the event of a collective response from Australia, Japan, the United States and potentially others. Indeed, thinkers in all three AJUS countries anticipate that, in the event of a high-end military conflict, the People’s Liberation Army (PLA) would pursue a regional-wide, theatre-level military campaign to complicate coalition operations far from the FIC.72 That potentiality has been illustrated by the PLA’s growing regional military presence, including the circumnavigation of Australia by a Chinese navy taskforce in late 2025, growing numbers of PLA forays into the greater Western Pacific and a longer history of Chinese military operations in the Indian Ocean.73
It follows, then, that a collective denial strategy along the FIC will be necessary but, in isolation, insufficient to address the magnitude of the defence challenges posed by the PLA. This will have implications for the ways in which the AJUS countries approach collective planning and coordination both with respect to the FIC and broader region, and the extent to which each of the AJUS countries anticipate their potential engagement in different imaginable high-end warfighting scenarios. In some ways, a theatre-wide framing makes Australia’s stakes in a wider trilateral regional defence strategy much clearer, closing the conceptual and psychological distance between the Australian mainland and the frontlines of that strategy compared with Japan’s geographical realities and the United States’ force posture along the FIC, and helping to rationalise the development of Australian defence infrastructure to support rear area operations for US and, increasingly, Japanese forces.74
2. Whether in deconflicting national efforts or pursuing collective planning, the three countries will need to set realistic expectations about their respective political thresholds for committing and using coordinated and/or combined force in a range of different scenarios. Notwithstanding their evident strategic alignment, all three contributors to this report highlighted the importance of achieving sufficient political consensus between the three national governments on a range of plausible regional developments as an important factor in the credibility and durability of a trilateral deterrence strategy, whether along the FIC or across the wider region. This will not be a ‘one and done’ effort, but a constant process of engagement and calibration, and one which the recently created Trilateral Defence Consultations (TDC) mechanism is primed to support.75
Communicating one another’s thresholds for national and collective action does not equal the pre-commitment to military action without first knowing the specific political and operational circumstances of a given contingency. Rather, understanding different constraining or limiting factors, and some degree of planning based on those assumptions will be, as one author in this compendium notes, an important prerequisite to “operate efficiently as distinct yet mutually supportive partners” in support of shared trilateral equities across a wide range of possible scenarios. Crucially, many imaginable FIC scenarios will not necessarily be the highest-end military contingencies and/or will not engage different AJUS partners’ respective national interests equally. A Chinese attack on or blockade of Taiwan often tends to overshadow contemporary discussions of regional defence challenges and alliance and security partnership dynamics, including at the official level,76 but a range of developments in the East China Sea or the South China Sea – or further abroad in the South Pacific or the Indian Ocean – below the threshold of kinetic military conflict may warrant a trilateral denial response. USSC simulation activities have also underscored how different crisis initiation dynamics and parallel contingencies across the region can stretch both force availability and the political willingness of different AJUS members to take different sorts of actions.77 Understanding these dynamics to the maximum extent possible ahead of potential challenges to regional stability ahead of time will be essential if deterrence is to hold and the prospect of trilateral action to support it is to be credible.
3. To mitigate political impediments to integration, experts suggest that the three countries should prioritise the development of operational integration, rather than simply fixating on a ‘gold standard’ of a unified command and control (C2) structure. Granted, the three countries are exploring options for embedding officers in one another’s command-and-control structures as an essential means for achieving a gold standard of military integration that may be required in the event of a high-end regional military conflict.78 Yet the contributions to this paper suggest that the AJUS countries could and should prioritise the development of tactical and operational integration, as well as the creation of bespoke trilateral institutions, to accelerate trilateral deterrence cooperation without the political difficulties of negotiating or relinquishing national control in a combined C2 arrangement.
To some extent, this is already occurring. For instance, the growing interchangeability between trilateral forces was recently demonstrated by the inaugural Exercise Southern Cross 26 in July 2026, during which Australian F-35s were flown and supported by a combination of pilots and ground crew from all three countries out of Australian airfields, and which also focused on forward arming and refuelling point (FARP) operations to improve trilateral sustainment.79 The three countries have also established new frameworks for operational information sharing in support of integrated air and missile defence cooperation and maritime domain awareness, and the new TDC mechanism to support “the alignment of policy and operational objectives.”80 And C2 engagements to date have focused on developing “essential enablers” of trilateral cooperation including “shared common operating pictures (COP), coordinated targeting processes and rapid decision-making mechanisms.”81 These efforts reflect both an expanding art of the possible and the real limitations that remain on a more formalised and concrete trilateral C2 structure, trends that have also been reflected in recent USSC simulations focused on integrated air and missile defence. These activities highlighted that even countries with deep and long-standing military relationships would prefer to pursue greater optionality through the development of practical mechanisms that could be rapidly escalated in support of operational cooperation in a crisis, rather than committing the political and practical capital required to build out those structures ahead of time.82
4. AJUS should double down on collective resilience measures — communications, cybersecurity, logistics and supply chains — to support both peacetime deterrence and potential wartime operational requirements. Even if political barriers remain to the highest standards of command integration and certain kinds of operational cooperation between the three countries, AJUS can make — and is making — progress on establishing a resilient basis for sustainable trilateral cooperation across the full spectrum of defence engagement, including deterrence along the FIC. All three contributions to this report recommend doubling down on efforts to improve trilateral capacity in areas of acute relevance to defence resilience: for instance, expanding cooperation in information-sharing, developing secure communications and cybersecurity protocols, strengthening regional logistics networks and closer coordination on shared defence supply chains. Each of these areas figure as ‘inputs’ into a collective deterrence strategy – as opposed to ‘outputs’ like military operations – and as enablers of more robust independent national defence capabilities with clear applications even before a conflict has broken out.
Such cooperation is equally relevant to supporting credible trilateral deterrence as it would be to trilateral warfighting. As the authors in this report and others in this AJUS series have noted, many forms of defence resilience are difficult to scale in wartime due to long technological or supply chain development timelines, the challenges of establishing logistics networks over vast maritime expanses while already under fire, the fiscal pressures of wartime economics, and other factors.83 Establishing the means to support sustained military operations through more assured access to communications, logistics and supply chains during peacetime will be essential well ahead of any prospective conflict, especially if it is to be protracted, while offering all three countries politically palatable options for advancing trilateral cooperation in more discrete but no less essential ways.
5. Effectively implementing denial along the First Island Chain — let alone across the wider region — will almost certainly require a broader coalition than AJUS alone, even if the trilateral remains the ‘core’ of a high-end military strategy. Even if other partners do not integrate or interoperate with the trilateral construct in the same way, the geography of the FIC and the nature of modern warfare mean that the cooperation of other partners — whether through information-sharing, access and overflight, industrial support or other means — will almost certainly be required if a FIC denial strategy is to be implemented in practice. Indeed, it is no coincidence that Australia, Japan and the United States have sought to greatly expand their military cooperation with the Philippines in recent years through negotiating access and information-sharing agreements and expanding the number and sophistication of military exercises, including several “Maritime Cooperative Activities.”84 Some former senior US defence leaders have even called for the institutionalisation of a new quadrilateral security grouping of these four countries — referred to colloquially by others as ‘the Squad’ — to constitute the core of a “Pacific Defence Pact.”85
There are good reasons why this is unlikely to happen in the near future, including the political and strategic costs of formalisation, and Manila’s comparative material and political capacity to contribute to a region-wide deterrence strategy beyond its local waters.86 Yet it is also the case that additional partner countries need not be as thoroughly integrated with the AJUS militaries to be capable of making meaningful contributions to a FIC denial strategy. The relatively recent addition of trilateral capacity-building and exercises with fourth and fifth partners, but particularly the Philippines, to the AJUS agenda in recent years hints at a coordinated effort to empower other regional states to better resist Chinese maritime coercion, whether acting independently or in concert with the trilateral.87 Doubling down on those parallel efforts will be an essential complement to building out the AJUS defence agenda.
