03 July 2026
CO26145 | The Sea Denial Trap: A Rejoinder
SYNOPSIS
Indonesia’s “sea denial” concept raises questions about its commitment to international law, including UNCLOS, the treaty that made its archipelagic statehood possible. In wartime, increasing the cost of access through Indonesian waters may inadvertently compromise Indonesia’s neutrality. Upholding international law remains Indonesia’s most credible and durable option.
COMMENTARY
This commentary is meant to add a dimension missing from the recent RSIS exchange between Indonesia’s Vice Minister for Foreign Affairs, Arif Havas Oegroseno, who floated a “sea denial” concept, and its critics, Professors Robert Beckman and Tommy Koh.
Vice Minister Oegroseno argues that the decisive maritime strategy of the 21st century is sea denial rather than sea control, and that Indonesia, as an archipelagic state commanding the region’s most critical sea lanes, is uniquely positioned to leverage this shift. He envisions a “third dimension of sea denial” achieved through kinetic means, such as missiles, drones, and naval mines. Professors Beckman and Koh respond that UNCLOS does not support any attempt by an archipelagic state to deny or restrict passage through its waters, and that Oegroseno’s reading of the law is flawed.
That the concept was put forward by Indonesia’s Vice Foreign Minister signals that this is not an academic exercise. That it leaves unspecified whether it concerns peacetime transit, wartime transit, or both, is what makes it worthwhile examining carefully. Neither commentary explicitly names the scenario that animates the entire debate. Yet every one of Oegroseno’s examples is a conflict scenario, a David versus Goliath story in which a weaker party denies access to a stronger one.
Read in that light, his commentary appears as a signal that Indonesia could make great-power transit costly in the event of a conflict. Indonesia has significant capacity constraints, and its sovereign legitimacy rests on UNCLOS, which explicitly prohibits suspending archipelagic sea lanes passage by any means. The question, therefore, is whether Indonesia would follow through on Oegroseno’s plan, and whether it should.
Kinetic Sea Denial – Why Now, Why Ever?
In peacetime, as Professors Beckman and Koh have noted, Oegroseno’s “sea denial” idea is unlawful under UNCLOS. In other words, should the plan materialise, Indonesia could find itself before UNCLOS’s compulsory dispute settlement mechanism. Beyond legality, the idea assumes Indonesia has no stake in the navigational rights it seeks to curtail for others. The recent Hormuz crisis, in which an Indonesian oil tanker owned by the country’s largest state-owned enterprise was stranded due to disrupted passage, shows that Indonesia depends on unrestricted access through the world’s other major chokepoints as much as others depend on free transit through Indonesian waters.
In wartime, the anxiety behind the “sea denial” idea is worth a closer look. Administering maritime neutrality is a serious burden for any state, let alone one whose geography spans seventeen thousand islands and has limited military resources. As Indonesia’s Acting Director-General for Legal Affairs and International Treaties, Dindin Wahyudin, has recently pointed out, the most acute scenario is not a deliberate attack on Indonesian territory but something more ambiguous: opposing belligerents simultaneously transiting the same archipelagic sea lane and engaging in crossfire during passage.
Even with such risks in wartime, archipelagic sea lanes passage through neutral waters remains non-suspendable under international law, even for belligerent forces. An archipelagic state’s neutrality is not affected by the mere passage of belligerent ships. However, when belligerents engage in hostile actions in neutral waters, such as the crossfire scenario described above, they violate the neutrality of the neutral state, and the neutral state is obliged to take measures necessary to terminate that violation. What those measures may look like in the specific context of an archipelagic state, however, remains an underdeveloped area of law, with state practice offering limited guidance.
Playing the Long Game
In a conflict between two great powers, keeping archipelagic sea lanes open, even when fully compliant with international law, may be seen as benefiting one side. Closing them, however, may also invite the same accusation, but without the protection of the law. That said, Indonesia’s neutrality will likely be questioned regardless, but only one of these options leaves it on the right side of international law.
If compliance with international law is considered not neutral, then what is? The alternative is the rule of power, which has never favoured small and middle-power states. Law is not a perfect shield, but it is the most durable and cost-efficient one available to a state in Indonesia’s position. And if more states begin to bend it and succumb to the rule of power, where does that lead if not to anarchy, in which small- and middle-power states lose the most – Indonesia among them.
Indonesia’s most defensible position is therefore not to develop capabilities to restrict passage, but to keep its archipelagic sea lanes open to all states in accordance with international law. To ease the burden of policing neutrality across its vast waters in wartime, Indonesia may lawfully suspend innocent passage through the remainder of its archipelagic waters on national security grounds.
This approach does three things: it honours Indonesia’s treaty obligations and protects its international credibility; it concentrates Indonesia’s limited military resources on securing the sea lanes against unintended conflict spillovers rather than dispersing them across all waters; and it signals to all parties that Indonesia is a principled neutral whose position is legally grounded and politically consistent.
Indonesia’s long-term interest thus lies in the integrity of international law and of UNCLOS in particular. As Oegroseno rightly noted, Indonesia’s archipelagic statehood was built through a quarter-century of diplomacy that persuaded a sceptical international community, including major powers that vigorously opposed the concept, to accept a new legal regime in exchange for guaranteed transit rights.
The “sea denial” framing risks historical amnesia about the terms of that bargain. Had the archipelagic state concept not been accepted in UNCLOS, the waters between Indonesia’s islands would be governed by high-seas freedoms, granting far greater navigational rights to foreign vessels than exist today, making it far harder for Indonesia to administer neutrality in wartime.
The archipelagic state regime also exists because of support from Indonesia’s trusted neighbours, including Singapore and Malaysia. Honouring international law, even in the most challenging contingency scenarios, is what keeps that trust intact and sustains Indonesian sovereignty in the long term.
About the Author
Dita Liliansa is a PhD candidate at the Faculty of Law and Justice, University of New South Wales, Sydney, Australia. Formerly a Research Fellow with the Ocean Law and Policy Programme at the NUS Centre for International Law, her latest work on belligerent activities in neutral EEZ was published in the International Review of the Red Cross.
SYNOPSIS
Indonesia’s “sea denial” concept raises questions about its commitment to international law, including UNCLOS, the treaty that made its archipelagic statehood possible. In wartime, increasing the cost of access through Indonesian waters may inadvertently compromise Indonesia’s neutrality. Upholding international law remains Indonesia’s most credible and durable option.
COMMENTARY
This commentary is meant to add a dimension missing from the recent RSIS exchange between Indonesia’s Vice Minister for Foreign Affairs, Arif Havas Oegroseno, who floated a “sea denial” concept, and its critics, Professors Robert Beckman and Tommy Koh.
Vice Minister Oegroseno argues that the decisive maritime strategy of the 21st century is sea denial rather than sea control, and that Indonesia, as an archipelagic state commanding the region’s most critical sea lanes, is uniquely positioned to leverage this shift. He envisions a “third dimension of sea denial” achieved through kinetic means, such as missiles, drones, and naval mines. Professors Beckman and Koh respond that UNCLOS does not support any attempt by an archipelagic state to deny or restrict passage through its waters, and that Oegroseno’s reading of the law is flawed.
That the concept was put forward by Indonesia’s Vice Foreign Minister signals that this is not an academic exercise. That it leaves unspecified whether it concerns peacetime transit, wartime transit, or both, is what makes it worthwhile examining carefully. Neither commentary explicitly names the scenario that animates the entire debate. Yet every one of Oegroseno’s examples is a conflict scenario, a David versus Goliath story in which a weaker party denies access to a stronger one.
Read in that light, his commentary appears as a signal that Indonesia could make great-power transit costly in the event of a conflict. Indonesia has significant capacity constraints, and its sovereign legitimacy rests on UNCLOS, which explicitly prohibits suspending archipelagic sea lanes passage by any means. The question, therefore, is whether Indonesia would follow through on Oegroseno’s plan, and whether it should.
Kinetic Sea Denial – Why Now, Why Ever?
In peacetime, as Professors Beckman and Koh have noted, Oegroseno’s “sea denial” idea is unlawful under UNCLOS. In other words, should the plan materialise, Indonesia could find itself before UNCLOS’s compulsory dispute settlement mechanism. Beyond legality, the idea assumes Indonesia has no stake in the navigational rights it seeks to curtail for others. The recent Hormuz crisis, in which an Indonesian oil tanker owned by the country’s largest state-owned enterprise was stranded due to disrupted passage, shows that Indonesia depends on unrestricted access through the world’s other major chokepoints as much as others depend on free transit through Indonesian waters.
In wartime, the anxiety behind the “sea denial” idea is worth a closer look. Administering maritime neutrality is a serious burden for any state, let alone one whose geography spans seventeen thousand islands and has limited military resources. As Indonesia’s Acting Director-General for Legal Affairs and International Treaties, Dindin Wahyudin, has recently pointed out, the most acute scenario is not a deliberate attack on Indonesian territory but something more ambiguous: opposing belligerents simultaneously transiting the same archipelagic sea lane and engaging in crossfire during passage.
Even with such risks in wartime, archipelagic sea lanes passage through neutral waters remains non-suspendable under international law, even for belligerent forces. An archipelagic state’s neutrality is not affected by the mere passage of belligerent ships. However, when belligerents engage in hostile actions in neutral waters, such as the crossfire scenario described above, they violate the neutrality of the neutral state, and the neutral state is obliged to take measures necessary to terminate that violation. What those measures may look like in the specific context of an archipelagic state, however, remains an underdeveloped area of law, with state practice offering limited guidance.
Playing the Long Game
In a conflict between two great powers, keeping archipelagic sea lanes open, even when fully compliant with international law, may be seen as benefiting one side. Closing them, however, may also invite the same accusation, but without the protection of the law. That said, Indonesia’s neutrality will likely be questioned regardless, but only one of these options leaves it on the right side of international law.
If compliance with international law is considered not neutral, then what is? The alternative is the rule of power, which has never favoured small and middle-power states. Law is not a perfect shield, but it is the most durable and cost-efficient one available to a state in Indonesia’s position. And if more states begin to bend it and succumb to the rule of power, where does that lead if not to anarchy, in which small- and middle-power states lose the most – Indonesia among them.
Indonesia’s most defensible position is therefore not to develop capabilities to restrict passage, but to keep its archipelagic sea lanes open to all states in accordance with international law. To ease the burden of policing neutrality across its vast waters in wartime, Indonesia may lawfully suspend innocent passage through the remainder of its archipelagic waters on national security grounds.
This approach does three things: it honours Indonesia’s treaty obligations and protects its international credibility; it concentrates Indonesia’s limited military resources on securing the sea lanes against unintended conflict spillovers rather than dispersing them across all waters; and it signals to all parties that Indonesia is a principled neutral whose position is legally grounded and politically consistent.
Indonesia’s long-term interest thus lies in the integrity of international law and of UNCLOS in particular. As Oegroseno rightly noted, Indonesia’s archipelagic statehood was built through a quarter-century of diplomacy that persuaded a sceptical international community, including major powers that vigorously opposed the concept, to accept a new legal regime in exchange for guaranteed transit rights.
The “sea denial” framing risks historical amnesia about the terms of that bargain. Had the archipelagic state concept not been accepted in UNCLOS, the waters between Indonesia’s islands would be governed by high-seas freedoms, granting far greater navigational rights to foreign vessels than exist today, making it far harder for Indonesia to administer neutrality in wartime.
The archipelagic state regime also exists because of support from Indonesia’s trusted neighbours, including Singapore and Malaysia. Honouring international law, even in the most challenging contingency scenarios, is what keeps that trust intact and sustains Indonesian sovereignty in the long term.
About the Author
Dita Liliansa is a PhD candidate at the Faculty of Law and Justice, University of New South Wales, Sydney, Australia. Formerly a Research Fellow with the Ocean Law and Policy Programme at the NUS Centre for International Law, her latest work on belligerent activities in neutral EEZ was published in the International Review of the Red Cross.
