When AUKUS Meets the Rule of Law

Last year, one of us wrote in Lawfare that AUKUS—the security pact among Australia, the United Kingdom, and the United States—raises questions that go well beyond military capabilities. Drawing on our “AUKUS and War Powers” report for King’s College London, the piece noted that while AUKUS might be premised on strategic and technological alignment, it also poses constitutional considerations. Consequently, the biggest obstacles it faces may not come from Beijing or Moscow, but from Canberra, London, and Washington.

In the year since that piece was published, the constitutional fault lines underlying U.S. foreign policy commitments have become even more visible, demonstrated most prominently by the November 2024 elections in the United States. The new administration has immediately and sharply demarcated itself from the policies of its predecessor, sending mixed messages over AUKUS and raising serious doubts among Britain and its European allies regarding America’s other security commitments, including NATO. On paper, it appears to be business as usual for AUKUS—but unusual business is afoot.

A new report published earlier this year, “AUKUS and Justiciability,” draws together judicial, academic, and strategic voices to revisit a legal doctrine long assumed to shield war powers from legal scrutiny. That doctrine—nonjusticiability—has traditionally insulated decisions about military deployment from judicial review. But across all three AUKUS countries, that insulation is increasingly open to challenge.

The report therefore charts a subtle but important shift. Courts are still reluctant to rule on foreign policy or defense operations, but they are no longer ruling them out entirely. AUKUS is often framed as a strategic and technological milestone, but this piece argues it is equally a constitutional experiment. As courts in Australia, the United Kingdom, and the United States become more willing to entertain challenges to military deployments and executive power, the long-assumed doctrine of nonjusticiability is eroding. Even unsuccessful litigation—on issues like Indigenous land rights, nuclear safety, or statutory authority—can introduce delays, caution, or political friction that undermine allied coherence. In a future crisis, this legal vulnerability could translate into strategic paralysis.

The Global War Powers Landscape

In Australia, Justice John Logan’s contribution to the report revisits the High Court’s logic in Ruddock v Vadarlis—where members of Australian Special Operations boarded a Norwegian vessel carrying asylum-seekers (without a statutory basis), ultimately found to be valid under executive power—and points out that while deployment decisions lie with the executive under Sections 61 and 68 of the Australian Constitution, they are not automatically immune from legal challenge. Where questions of legality, statutory interpretation, or rights arise, courts may well feel obligated to step in. This is particularly the case if there is a perception that the executive has acted beyond the scope of its powers, evading proper political consultation with the legislative branch of government (such as, say, the domestic deployment of troops in a federal construct).

Perhaps even more complicated is the executive exercise of prerogative powers to deploy combat-ready forces for deterrent effect—what might be characterized as “military diplomacy.” Such deployments are intended to avoid the invocation of war powers through coalition action that signals the resolve of partner nations. This is ultimately a matter for the executive to decide upon, even if civil society (and, if litigated, the courts) disagree. In that twilight zone between diplomacy and military action, or peace and war, the judicial willingness to intercede seems even more dubious, and the justiciability obstacle even more daunting.

In the United Kingdom, while prerogative powers afford the executive broader discretion than the U.S. or Australia, the constitutional shield of nonjusticiability provided to war and foreign affairs has also come into question. There remains a reluctance among the judiciary to address issues regarding military operations, yet the long-standing assumptions of prerogative imperviousness to judicial scrutiny in matters of “high politics” (such as deploying troops, or proroguing Parliament) are no longer inherent in practice. While this may not substantively change how cases are ruled upon, such uncertainty leaves the door open to hypothetical challenges hitherto thought to be nonjusticiable. At the most extreme end, in crises this may influence strategic behavior and incentivize undue operational caution in government or parliament.

Some observers may find solace in the recent dismissal of a legal challenge brought over the transfer of sovereignty for the strategically important Chagos Island Archipelago from the United Kingdom to Mauritius. The plight of the Chagossian people and the strategic ramifications of this decision notwithstanding, a legal challenge to the Crown’s prerogative to authorize this transfer of sovereignty was unlikely to succeed, and from a military perspective suggests similar challenges to deployment decision would also be dismissed.

As such, these are not just matters of legal theory. What is at stake here is the very operability of AUKUS in moments of crisis. Strategic alliances require not just political will and shared threat perceptions, but timely decisions and unified action. If a future crisis in the Indo-Pacific requires a coordinated AUKUS deployment, but one partner is faced with litigation or domestic legal hurdles, that coherence collapses. Legal uncertainty becomes strategic liability.

Impacts on AUKUS

This is not a hypothetical concern. Already, civil society actors and issue-motivated groups across the AUKUS states are beginning to mobilize against the pact—not just on strategic grounds, but through the courts. In Australia, concerns over nuclear safety, Indigenous land rights, and the extraordinary scale of the AUKUS budget (projected at AUD $400 billion) have become touchstones for opposition movements. What begins as a protest can quickly become a judicial review. If there is a statute to test, or a regulatory approval to challenge, there is a potential point of leverage.

The point is not that these groups will necessarily win. But in an age of political fragmentation and legal activism, the mere act of litigation can introduce delay, caution, or doubt into executive planning. The doctrine of nonjusticiability is no longer a blank check. A claim doesn’t have to succeed to have an effect—it just has to be arguable.

We’ve already seen this play out in neighboring New Zealand, where protests and petitions forced parliamentary debate over involvement in U.S.-led naval exercises. Though New Zealand is not an AUKUS partner, the public’s reaction there is an early signal of how domestic democratic processes can disrupt strategic planning, even in countries that broadly support U.S. security partnerships. In the United Kingdom, there is a general convention of judicial non-interference in matters of foreign affairs and agreement that domestic constitutional law outranks international legal obligations. However, jurisprudential developments both in the United Kingdom and in Commonwealth realms like Canada have shown that not all executive decisions under the royal prerogative are inherently exempt from examination. And in the United States, war powers debates have become increasingly pointed, with congressional frustrations spilling into the courts—albeit constrained by doctrines of standing and political questions.

What complicates all this further is the unpredictability of the U.S. political scene. Last year, former President Trump was asked what he thought of AUKUS. His answer—“What does that mean?”—was less a gaffe than a warning. The agreement may be a top-tier priority for Canberra and London, but in Washington, it remains vulnerable to shifting winds. Trump’s indifference has since hardened into something closer to hostility. His recent criticisms of NATO and lukewarm support for Indo-Pacific partnerships raise the real possibility that a second Trump administration could sideline or slow-walk AUKUS implementation. This would likely occur by introducing transactional conditions, dragging out timelines, or cutting funding, rather than through a formal withdrawal, which at this stage would be too politically costly for relations among the three allies. As with other more explicit security agreements like NATO, formal withdrawal is not necessary to terminate AUKUS in practice; the mere signaling of intent and gradual drawdown of resources is more than sufficient.

That is why the question of justiciability matters. Not because courts are likely to overrule deployment decisions—but because they may increasingly be asked to. Once a court entertains the question, even to dismiss it, the political landscape changes. Executive power no longer enjoys the special preeminence in foreign affairs that was once presupposed by civil society. Nor are understandings of constitutional history and practice as strong as they once were, particularly in the political sphere. That perception alone is enough to embolden those seeking to delay decisions or complicate coordination among allies.

In that climate, the risk of legal action becomes more than a technical matter. If one partner’s courts allow a challenge, for example, to a contentious submarine deployment, or if a parliament demands authorization for force, and another executive presses ahead without delay, then AUKUS fractures in practice even if it holds on paper. The effect may be a kind of strategic stutter: hesitation, inconsistency, or misalignment when unity is most needed.

In the AUKUS context, the submarine is not just a weapon platform—it is a legal symbol. It embodies all the anxieties of 21st-century warfare: secrecy, deterrence, preemption, and now, judicial scrutiny. When an AUKUS-acquired submarine is eventually deployed into contested waters amid heightened international tensions, the questions won’t just be “Where is it going?” or “What is it doing?” but “Who authorized it?” “Who’s accountable?” and potentially, “Can this be challenged in court?”

Confronting the Challenge

To address these issues, the public and government officials must first recognize them as problems. The constitutional dimension of foreign affairs cannot be ignored. Looking to historical and political practice, including drawing on executive and legislative positions on Cold War joint-crewed naval exercises and operations, may prove one avenue for military planners, lawyers, and government strategists. Equally, the development and promulgation of a doctrine for joint-crewed, interoperable capabilities such as AUKUS may help bolster the agreement’s strength, while inoculating it against prospective legal challenges. A more thorough awareness of what can be successfully challenged in court can help governments and legislatures in these AUKUS allies preempt undue operational stresses in periods of crisis. While this will not overcome the inherent political problems that may arise among allies over contentious deployment issues—issues common to many operations since 1945—it can dull the edge of legal ones.

AUKUS is often presented purely in technical terms—a significant strategic leap forward, anchoring U.S. commitment to the region and delivering cutting-edge capabilities to Australia. But it is also something more delicate: a constitutional experiment. Can three liberal democracies with distinct legal traditions maintain a credible deterrent when their executives no longer operate in a legal vacuum? Can they act together when each must look over its legal shoulder?

Those are not the kinds of questions usually asked in defense white papers. But they are the ones that will shape the alliance’s future. Submarines may move silently beneath the waves, but the legal arguments circling above them are getting louder every day.