03 July 2026
CO26144 | Indonesia’s Archipelagic Power and How Best to Sustain It
SYNOPSIS
Indonesia’s leverage as an archipelagic state comes from being the custodian of open straits. Sea denial offers little that custodianship does not already provide, and for a state bound together by its own sea lanes, the precedent of closing a waterway threatens the integrity of the archipelago itself.
COMMENTARY
Indonesian Vice Minister for Foreign Affairs Arif Havas Oegroseno’s RSIS commentary on 22 June 2026 highlights a long-standing ambition shared by many in Indonesia’s defence and foreign policy establishment: that Indonesia, as the natural custodian of three of the world’s critical chokepoints, should hold strategic weight commensurate with its geography.
This is a reasonable aspiration, underlined by fears that a great-power conflict would turn Indonesia’s archipelagic waters into a battleground. Indonesia is also concerned about American infringements into Indonesia’s maritime and aerial spaces, as well as Chinese encroachments off Natuna.
Oegroseno indicates that such a sea denial capability, as latent leverage against future contingencies, would benefit Indonesia and other coastal states. While we agree that Indonesia should build real maritime power, the surer road for using that power runs through the custodianship of open straits rather than their denial.
Indonesia is the chief beneficiary of UNCLOS, but it is not a one-way street
First, UNCLOS is of foundational importance to Indonesia, which has every interest in upholding it. UNCLOS not only doubled Indonesia’s maritime jurisdiction but also imbued the nation with a sense of unity. Through wawasan Nusantara and the archipelagic state regime under UNCLOS, Indonesia regarded the ocean as a unifying factor.
However, the recognition of Indonesia as an archipelagic state entails a quid pro quo, including navigation rights granted to user states: passage through archipelagic sea lanes under Article 53 and innocent passage under Article 52.
Indonesia may adopt laws on the safety of navigation, pollution and fishing, but such laws may not deny, hamper or impair archipelagic sea lanes passage. As one of the coastal states along the Straits of Malacca and Singapore, Indonesia has the obligation to ensure transit passage and cannot hamper the rights of transit.
Much depends on whether Indonesia is neutral or belligerent. If Indonesia is a neutral state in a conflict scenario, it has the obligation to ensure transit passage and to keep archipelagic sea lanes open. As a belligerent, an anti-access/aerial denial (A2AD) strategy and the closure of certain straits could become an option under the law of naval blockade.
Custodianship versus Denial
Second, sea denial may be meant as either a peacetime posture or a wartime capability, and the two must be assessed separately. Carried to its conclusion, a denial posture points towards an A2AD buildup by a coalition of coastal states, but these do not necessarily face the same threats, making such a coalition difficult to form.
More fundamentally, peacetime closure is simply unlawful. UNCLOS permits no suspension of transit or archipelagic sea lanes passage, so denial is an option open to Indonesia only if it is a belligerent. A further problem is structural. A norm that legitimises closure and signals such an intent gives the same leverage to other states situated alongside contestable chokepoints.
In contrast, a viable cooperative model already exists, and Indonesia is one of its co-architects. Since 2007, the Straits of Malacca and Singapore have been managed under the Cooperative Mechanism, which provides a forum for dialogue and for maintaining navigational aids. The Malacca Straits Sea and Air Patrol, conducted by Indonesia alongside Malaysia, Singapore and Thailand, has likewise suppressed piracy in the same waters. This preserves the sovereign interests of the littoral states while guaranteeing free passage in peacetime.
The Lesson from Hormuz
Third, if denial is a wartime capability, the lesson we draw from Hormuz is a different one. Iran raised the costs of American naval operations in Hormuz by hardening Iranian infrastructure against air strikes, developing sophisticated drone and missile capabilities, and withstanding immense economic punishment. Replicating such a playbook is both costly and runs counter to Indonesia’s national goal of promoting economic prosperity and welfare for its people.
Indonesia’s geography also differs from Iran’s. Iran weaponised a single narrow strait, whose approaches are easily monitored and defended. On the other hand, Indonesia’s seascape is vast and fragmented, making any hostile approach far harder to anticipate.
Indonesia’s viability as an archipelagic state depends on keeping its internal maritime lines of communication between its 17,000 islands. The Indonesian word for homeland is tanah air (land and sea), highlighting the indivisibility of land and water. Closing those waters against an enemy in war through mining operations also impedes domestic shipping and internal logistical links. Precision interdiction by missile and drone avoids this, but it requires significant monitoring of likely approaches and the dispersal of capabilities across multiple sea lanes, requiring a far larger and costlier architecture than at the Strait of Hormuz.
Archipelagic Power
The development of archipelagic power, which combines the concentration of forces within joint regional defence commands with the mobility to relieve beleaguered positions and the dispersal of A2AD capabilities will likely shape the strategic calculations of great powers.
However, a denial capability would secure little that custodianship does not already grant Indonesia. Indonesia’s interests in the Straits of Malacca and Singapore are accommodated by the Cooperative Mechanism, and it already enjoys full management of its second and third archipelagic sea lanes. Denial would add little to this. It would not even confer a wartime closure right for warships of the kind the Montreux Convention grants Turkey, since Indonesia’s straits remain governed by UNCLOS, under which passage cannot be suspended. The capability offers leverage Indonesia already largely possesses.
Indonesian statecraft has always combined the force of arms with diplomacy. The Republic was not won by armed struggle alone, but by astute diplomacy at the negotiating table. It was the same tradition that secured Indonesia’s archipelagic status during the UNCLOS negotiations and which President Prabowo Subianto affirmed at the UN in September 2025, when he said that “might cannot be right”.
Perhaps the surer road lies in custodianship, not denial. The United States never ratified UNCLOS. China ratified it, then pressed claims in the South China Sea that an arbitral tribunal rejected in 2016. Neither can be relied on to keep the sea lanes open. No state has a more enduring interest in open waters than Indonesia, and its power grows not from the threat to close the straits but from being their custodian.
About the Authors
Jefferson Ng is a PhD candidate in the Department of Political and Social Change, at the Australian National University. Aristyo Rizka Darmawan is an Assistant Professor of International Law at Universitas Indonesia and a PhD candidate at the Australian National University.
SYNOPSIS
Indonesia’s leverage as an archipelagic state comes from being the custodian of open straits. Sea denial offers little that custodianship does not already provide, and for a state bound together by its own sea lanes, the precedent of closing a waterway threatens the integrity of the archipelago itself.
COMMENTARY
Indonesian Vice Minister for Foreign Affairs Arif Havas Oegroseno’s RSIS commentary on 22 June 2026 highlights a long-standing ambition shared by many in Indonesia’s defence and foreign policy establishment: that Indonesia, as the natural custodian of three of the world’s critical chokepoints, should hold strategic weight commensurate with its geography.
This is a reasonable aspiration, underlined by fears that a great-power conflict would turn Indonesia’s archipelagic waters into a battleground. Indonesia is also concerned about American infringements into Indonesia’s maritime and aerial spaces, as well as Chinese encroachments off Natuna.
Oegroseno indicates that such a sea denial capability, as latent leverage against future contingencies, would benefit Indonesia and other coastal states. While we agree that Indonesia should build real maritime power, the surer road for using that power runs through the custodianship of open straits rather than their denial.
Indonesia is the chief beneficiary of UNCLOS, but it is not a one-way street
First, UNCLOS is of foundational importance to Indonesia, which has every interest in upholding it. UNCLOS not only doubled Indonesia’s maritime jurisdiction but also imbued the nation with a sense of unity. Through wawasan Nusantara and the archipelagic state regime under UNCLOS, Indonesia regarded the ocean as a unifying factor.
However, the recognition of Indonesia as an archipelagic state entails a quid pro quo, including navigation rights granted to user states: passage through archipelagic sea lanes under Article 53 and innocent passage under Article 52.
Indonesia may adopt laws on the safety of navigation, pollution and fishing, but such laws may not deny, hamper or impair archipelagic sea lanes passage. As one of the coastal states along the Straits of Malacca and Singapore, Indonesia has the obligation to ensure transit passage and cannot hamper the rights of transit.
Much depends on whether Indonesia is neutral or belligerent. If Indonesia is a neutral state in a conflict scenario, it has the obligation to ensure transit passage and to keep archipelagic sea lanes open. As a belligerent, an anti-access/aerial denial (A2AD) strategy and the closure of certain straits could become an option under the law of naval blockade.
Custodianship versus Denial
Second, sea denial may be meant as either a peacetime posture or a wartime capability, and the two must be assessed separately. Carried to its conclusion, a denial posture points towards an A2AD buildup by a coalition of coastal states, but these do not necessarily face the same threats, making such a coalition difficult to form.
More fundamentally, peacetime closure is simply unlawful. UNCLOS permits no suspension of transit or archipelagic sea lanes passage, so denial is an option open to Indonesia only if it is a belligerent. A further problem is structural. A norm that legitimises closure and signals such an intent gives the same leverage to other states situated alongside contestable chokepoints.
In contrast, a viable cooperative model already exists, and Indonesia is one of its co-architects. Since 2007, the Straits of Malacca and Singapore have been managed under the Cooperative Mechanism, which provides a forum for dialogue and for maintaining navigational aids. The Malacca Straits Sea and Air Patrol, conducted by Indonesia alongside Malaysia, Singapore and Thailand, has likewise suppressed piracy in the same waters. This preserves the sovereign interests of the littoral states while guaranteeing free passage in peacetime.
The Lesson from Hormuz
Third, if denial is a wartime capability, the lesson we draw from Hormuz is a different one. Iran raised the costs of American naval operations in Hormuz by hardening Iranian infrastructure against air strikes, developing sophisticated drone and missile capabilities, and withstanding immense economic punishment. Replicating such a playbook is both costly and runs counter to Indonesia’s national goal of promoting economic prosperity and welfare for its people.
Indonesia’s geography also differs from Iran’s. Iran weaponised a single narrow strait, whose approaches are easily monitored and defended. On the other hand, Indonesia’s seascape is vast and fragmented, making any hostile approach far harder to anticipate.
Indonesia’s viability as an archipelagic state depends on keeping its internal maritime lines of communication between its 17,000 islands. The Indonesian word for homeland is tanah air (land and sea), highlighting the indivisibility of land and water. Closing those waters against an enemy in war through mining operations also impedes domestic shipping and internal logistical links. Precision interdiction by missile and drone avoids this, but it requires significant monitoring of likely approaches and the dispersal of capabilities across multiple sea lanes, requiring a far larger and costlier architecture than at the Strait of Hormuz.
Archipelagic Power
The development of archipelagic power, which combines the concentration of forces within joint regional defence commands with the mobility to relieve beleaguered positions and the dispersal of A2AD capabilities will likely shape the strategic calculations of great powers.
However, a denial capability would secure little that custodianship does not already grant Indonesia. Indonesia’s interests in the Straits of Malacca and Singapore are accommodated by the Cooperative Mechanism, and it already enjoys full management of its second and third archipelagic sea lanes. Denial would add little to this. It would not even confer a wartime closure right for warships of the kind the Montreux Convention grants Turkey, since Indonesia’s straits remain governed by UNCLOS, under which passage cannot be suspended. The capability offers leverage Indonesia already largely possesses.
Indonesian statecraft has always combined the force of arms with diplomacy. The Republic was not won by armed struggle alone, but by astute diplomacy at the negotiating table. It was the same tradition that secured Indonesia’s archipelagic status during the UNCLOS negotiations and which President Prabowo Subianto affirmed at the UN in September 2025, when he said that “might cannot be right”.
Perhaps the surer road lies in custodianship, not denial. The United States never ratified UNCLOS. China ratified it, then pressed claims in the South China Sea that an arbitral tribunal rejected in 2016. Neither can be relied on to keep the sea lanes open. No state has a more enduring interest in open waters than Indonesia, and its power grows not from the threat to close the straits but from being their custodian.
About the Authors
Jefferson Ng is a PhD candidate in the Department of Political and Social Change, at the Australian National University. Aristyo Rizka Darmawan is an Assistant Professor of International Law at Universitas Indonesia and a PhD candidate at the Australian National University.
