The volatile security environment in the Middle East has provided a stark wake-up call for Canberra. The recurring instability and threats of closure in the Strait of Hormuz have underscored a fundamental geopolitical reality: Australia remains profoundly dependent on a handful of global maritime chokepoints to sustain its economy and national security.
While the Hormuz crisis is geographically distant, it has highlighted a more immediate vulnerability closer to home. Australia’s reliance on Australia’s Indonesian sea lanes—the intricate network of straits and archipelagic passages through the Indonesian archipelago—represents a critical point of failure. As the vast majority of Australia’s trade flows through these waters, any disruption would not merely be an economic inconvenience; it would be existential.
The scale of this dependency is immense. Routes passing through or around Indonesia account for approximately 83% of Australia’s maritime imports and around 90% of its exports. These lanes, including the Strait of Malacca and the Lombok and Sunda straits, serve as the primary arteries for the nation’s fuel, food, and industrial supplies.
To mitigate these risks, Australia and Indonesia have moved toward a more formalized security architecture. The February 2026 signing of the Australia–Indonesia Treaty on Common Security, known as the Jakarta Treaty, establishes a framework for regular ministerial and leadership consultations. This treaty is designed to create the diplomatic conditions necessary to ensure these vital waterways remain open, even during periods of regional tension.
The Legal Friction: UNCLOS and the Right of Passage
The stability of these sea lanes rests on a complex interpretation of international law. Under the United Nations Convention on the Law of the Sea (UNCLOS), Indonesia is generally obliged to ensure that its archipelagic sea lanes remain open for international navigation. This obligation is further reinforced for neutral countries during armed conflicts by the San Remo and Newport Manuals.
However, there is a significant legal gray area regarding the “substitution” of lanes. Article 53 (7) of UNCLOS states that an archipelagic state may, when circumstances require and after providing due publicity, substitute other sea lanes. This provision has been a point of contention between Jakarta and other maritime powers.
Historical precedents illustrate how this legal ambiguity can lead to diplomatic crises. In 1964, during a period of “confrontation” with Malaysia, Indonesia denied the British aircraft carrier HMS Victorious and two destroyers passage through the Sunda Strait while they were traveling from Perth to Singapore. Though this occurred before UNCLOS was established, it set a precedent for how Jakarta might use its geography as a tool of foreign policy.
Decades later, in 1988, Indonesia closed both the Sunda and Lombok straits for military exercises. This move triggered a sharp response from the Australian government, which argued that the closure violated international law. The tension underscores a persistent divide: while some legal experts argue these are “straits normally used for international navigation” and must remain open, Indonesian naval officials have maintained that the state retains the right to redirect traffic to substitute lanes if necessary.
| Year | Incident | Impact/Outcome |
|---|---|---|
| 1964 | HMS Victorious denied passage in Sunda Strait | Tension between UK and Indonesia; resolved via alternative routes. |
| 1988 | Sunda and Lombok straits closed for exercises | Diplomatic protest from Canberra over international law violations. |
| 2026 | Signing of the Jakarta Treaty | Established formal security cooperation to prevent future closures. |
A2/AD Capabilities and the AUKUS Factor
The debate over sea lanes is moving beyond theoretical law into the realm of military capability. Recent research from the International Institute for Strategic Studies (IISS) indicates that Indonesia is integrating anti-access/area-denial (A2/AD) strategies into its archipelagic defense. This includes the deployment of naval mines and submarines specifically positioned around “strategic funnels” in Indonesian waters.
This shift in defense posture coincides with a critical ambiguity in how Indonesia designates its sea lanes. Currently, only parts of its archipelagic sea lanes are officially designated. For example, the east-west lanes through the Java Sea remain undesignated. This creates a legal vacuum regarding the status of passage in those specific areas.
The distinction between “archipelagic sea lane passage” and other forms of transit is not merely academic; it has profound implications for the AUKUS security pact. The legal status of a lane determines whether a submarine must remain submerged or is required to show its flag. As AUKUS-funded submarines begin to traverse these straits in the coming years, the lack of clear designation in certain waters could lead to dangerous miscalculations or diplomatic stand-offs.
Strategic Next Steps for Canberra and Jakarta
The lesson from the Strait of Hormuz is that international law, while essential, is often insufficient on its own to prevent the closure of a chokepoint during a crisis. Reliance on UNCLOS alone is a gamble when faced with a state’s perceived national security necessity.
To avoid a future crisis, the focus must shift toward operational communication and contingency planning. The Jakarta Treaty provides the mechanism for this, allowing for high-level consultations on common security. The objective for both nations is to move toward a shared understanding of how to regulate these lanes, specifically during times of conflict, to ensure that trade does not grind to a halt.
A report from the Center for Strategic and International Studies (CSIS) has suggested that the United States should increase freedom-of-navigation operations (FONOPS) around Indonesia to discourage closures. However, for Australia, the priority remains a bilateral relationship with Jakarta based on transparency and mutual security guarantees.
The next critical checkpoint for this relationship will be the initial implementation phase of the Jakarta Treaty’s consultation forums, where both nations are expected to begin drafting contingency scenarios for maritime transit. These meetings will determine whether the “existential” risk of a sea-lane closure can be managed through diplomacy before a crisis forces the issue.
This article is provided for informational purposes and does not constitute legal advice regarding maritime law or international treaties.
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