22 June 2026
CO26133 | The Sea Denial Trap: Why the Age of Unrestricted Sea Power Is Ending
SYNOPSIS
From the Black Sea to the Red Sea, powerful navies are finding that access to contested waters can no longer be taken for granted. The decisive maritime strategy of the 21st century is not sea control but sea denial — and its true pioneer was not a great power but an archipelagic one. For the middle powers of the Indo-Pacific, this is not a threat to be managed. It is leverage waiting to be seized.
COMMENTARY
In 2022, Ukraine — a state with effectively no navy — forced the Russian Black Sea Fleet to abandon its main base at Sevastopol using drones and shore-launched missiles. Since 2023, the Houthis, a non-state actor, have rerouted a measurable share of global container traffic away from the Red Sea using weapons that cost a fraction of the value of the vessels they threaten. Iran has held the Strait of Hormuz at risk without fighting a single fleet action. The pattern is unmistakable: cheap precision weapons, hostile geography, and political resolve are defeating expensive tonnage.
Naval orthodoxy still treats these as anomalies — irritants to be managed until proper sea control is restored. But they are not anomalies. They are the visible edge of a structural shift that strategists have been slow to name: the superior naval power loses its advantage at the point when the cost of access — operational, financial, political, and legal — exceeds the strategic value of what that access secures. Call it the Sea Denial Trap. A fleet does not need to be defeated to be defeated; it merely needs to be priced out of the water.
An Old Pattern, Newly Armed
History has been teaching this lesson for 2,500 years. At Salamis in 480 BCE, Themistocles lured a Persian fleet twice his size into a strait where its numbers became a liability. At Myeongnyang in 1597, Korean Admiral Yi Sun-sin destroyed a Japanese armada of more than 130 warships with only thirteen ships by weaponising a tidal channel. In 1527 at Sunda Kelapa — present-day Jakarta — Fatahillah’s force of small traditional vessels denied Portugal, then the world’s premier maritime empire, a fortified foothold in Java. In each case, the weaker party prevailed not by contesting command of the sea but by rendering a specific body of water unusable to a superior fleet at an acceptable moment and price.
What has changed is that technology has democratised what geography once monopolised. Anti-ship missiles, commercially available or cheap drones, sea mines, and ubiquitous sensors now enable a middle power to replicate the same cost asymmetry along any coastline, including strategic straits. The cost of sea denial has collapsed precisely as the cost of blue-water fleets has soared.
Indonesia’s Forgotten Invention
Yet the most consequential act of sea denial in modern history involved no weapons at all. On 13 December 1957, the Djuanda Declaration asserted that the waters between Indonesia’s islands were not high seas but part of the internal fabric of a single archipelagic state. The reaction revealed the stakes: Seven maritime powers — the United States, the United Kingdom, France, Australia, the Netherlands, New Zealand, and Japan — lodged formal protests, all on the same ground, i.e., that Indonesia had converted long-recognised high seas into national waters. Twenty-five years of disciplined diplomacy later, the archipelagic state regime was codified in Part IV of UNCLOS. Indonesia had redrawn the legal geography of the ocean: What foreign navies had treated as open water became, in law, Indonesian waters.
The resistance was not confined to diplomatic notes. Britain protested with warships: In August 1964, at the height of Konfrontasi, the carrier HMS Victorious and two escorts steamed through the Sunda Strait — a passage Indonesia claimed as sovereign — as a deliberate show of strength, on barely two days’ informal notice. Jakarta barred the return passage, and for two weeks the two governments stood on the brink of open conflict before a compromise routed the carrier home through the Lombok Strait. It was, in effect, the first freedom-of-navigation operation ever mounted against the archipelagic claim: a Mahanian navy asserting, by its presence, the access that Indonesian law sought to deny.
The other protesters reveal why the claim cut so deep. Australia, the only neighbour among them, saw the contested straits as its commercial lifelines to Asia and Europe — the Victorious was itself en route to Australia when the 1964 crisis erupted. Japan was the most exposed of all: the overwhelming bulk of its oil moved from the Persian Gulf through the Straits of Malacca and Singapore, Sunda, Lombok, and Makassar, and American analysts in the early 1970s assessed that an Indonesian restriction on passage would lay a hand on the Japanese economy’s jugular. Declassified American records show that Washington, too, understood precisely what was at stake. An 1973 CIA assessment concluded that Indonesia sought the right to deny use of the sea lanes crossing its archipelago. By 1974 the matter had escalated to personal correspondence between Presidents Nixon and Suharto.
This was sea denial in a second dimension — legal-diplomatic rather than kinetic — and it achieved what capital ships could not. That every major maritime power protested, and that one sent an aircraft carrier, is the measure of what the declaration threatened. Indonesia, without a blue-water navy, raised the legal and political cost of unrestricted access until the world’s strongest maritime powers accepted a new rule, balanced by archipelagic sea lanes passage. No other state has executed denial on that scale by legal means.
Indonesia’s geography provides the first dimension. Three of the world’s critical chokepoint systems — the Straits of Malacca and Singapore, Sunda, and Lombok–Ombai–Wetar — pass through or alongside its waters. Seventeen thousand islands form a natural defensive battlespace in which any intruding fleet faces Xerxes’ problem at Salamis: seas that turn numerical superiority into vulnerability.
The third dimension — affordable kinetic denial through missiles, drones, submarines, and mine warfare — is the one Indonesia is also developing. Ukraine and the Red Sea demonstrate how decisively that gap can now be closed, and how cheaply relative to a conventional fleet build-up.
Leverage for the Region
For most of the world’s maritime states, the strategic question of this century is not how to command the sea — they never will — but how to prevent the sea from being commanded against them. The Sea Denial Trap reframes their position. Geography, international law, and asymmetric technology are not consolation prizes for states without carriers; when deliberately combined, they form a strategy that has repeatedly defeated carrier groups.
The archipelagic and middle powers of the Indo-Pacific — Indonesia, the Philippines, Malaysia, Vietnam, Sri Lanka — hold more leverage than tonnage tables suggest. A coalition of archipelagic and coastal states defending and extending the UNCLOS regime they co-authored would be more durable than any unilateral posture — and more credible than any externally supplied security guarantee.
For great powers, the implications are sobering. Every projection of naval force into littoral Asia now runs through waters where the trap can be set — legally through coastal state rights under UNCLOS, geographically through straits and island chains, and kinetically through weapons any middle power can field. The era in which a superior fleet could have access at acceptable cost is closing. Mahan taught the world to count battleships. The century ahead will belong to those who count chokepoints, legal entitlements, and the price of admission.
Indonesia articulated this logic before anyone else — in 1957, in the language of law rather than firepower — and the protests of seven maritime powers, sustained for a quarter of a century, proved that the world’s naval fleets understood it. It is time the doctrine bore an archipelagic name.
About the Author
Arif Havas Oegroseno is the Vice Minister for Foreign Affairs of the Republic of Indonesia. He has been a negotiator of maritime boundary agreements and has written extensively on the law of the sea and the doctrine of the archipelagic state. He was the President of the 20th Meeting of States Parties to UNCLOS 1982. The views expressed are his own.
SYNOPSIS
From the Black Sea to the Red Sea, powerful navies are finding that access to contested waters can no longer be taken for granted. The decisive maritime strategy of the 21st century is not sea control but sea denial — and its true pioneer was not a great power but an archipelagic one. For the middle powers of the Indo-Pacific, this is not a threat to be managed. It is leverage waiting to be seized.
COMMENTARY
In 2022, Ukraine — a state with effectively no navy — forced the Russian Black Sea Fleet to abandon its main base at Sevastopol using drones and shore-launched missiles. Since 2023, the Houthis, a non-state actor, have rerouted a measurable share of global container traffic away from the Red Sea using weapons that cost a fraction of the value of the vessels they threaten. Iran has held the Strait of Hormuz at risk without fighting a single fleet action. The pattern is unmistakable: cheap precision weapons, hostile geography, and political resolve are defeating expensive tonnage.
Naval orthodoxy still treats these as anomalies — irritants to be managed until proper sea control is restored. But they are not anomalies. They are the visible edge of a structural shift that strategists have been slow to name: the superior naval power loses its advantage at the point when the cost of access — operational, financial, political, and legal — exceeds the strategic value of what that access secures. Call it the Sea Denial Trap. A fleet does not need to be defeated to be defeated; it merely needs to be priced out of the water.
An Old Pattern, Newly Armed
History has been teaching this lesson for 2,500 years. At Salamis in 480 BCE, Themistocles lured a Persian fleet twice his size into a strait where its numbers became a liability. At Myeongnyang in 1597, Korean Admiral Yi Sun-sin destroyed a Japanese armada of more than 130 warships with only thirteen ships by weaponising a tidal channel. In 1527 at Sunda Kelapa — present-day Jakarta — Fatahillah’s force of small traditional vessels denied Portugal, then the world’s premier maritime empire, a fortified foothold in Java. In each case, the weaker party prevailed not by contesting command of the sea but by rendering a specific body of water unusable to a superior fleet at an acceptable moment and price.
What has changed is that technology has democratised what geography once monopolised. Anti-ship missiles, commercially available or cheap drones, sea mines, and ubiquitous sensors now enable a middle power to replicate the same cost asymmetry along any coastline, including strategic straits. The cost of sea denial has collapsed precisely as the cost of blue-water fleets has soared.
Indonesia’s Forgotten Invention
Yet the most consequential act of sea denial in modern history involved no weapons at all. On 13 December 1957, the Djuanda Declaration asserted that the waters between Indonesia’s islands were not high seas but part of the internal fabric of a single archipelagic state. The reaction revealed the stakes: Seven maritime powers — the United States, the United Kingdom, France, Australia, the Netherlands, New Zealand, and Japan — lodged formal protests, all on the same ground, i.e., that Indonesia had converted long-recognised high seas into national waters. Twenty-five years of disciplined diplomacy later, the archipelagic state regime was codified in Part IV of UNCLOS. Indonesia had redrawn the legal geography of the ocean: What foreign navies had treated as open water became, in law, Indonesian waters.
The resistance was not confined to diplomatic notes. Britain protested with warships: In August 1964, at the height of Konfrontasi, the carrier HMS Victorious and two escorts steamed through the Sunda Strait — a passage Indonesia claimed as sovereign — as a deliberate show of strength, on barely two days’ informal notice. Jakarta barred the return passage, and for two weeks the two governments stood on the brink of open conflict before a compromise routed the carrier home through the Lombok Strait. It was, in effect, the first freedom-of-navigation operation ever mounted against the archipelagic claim: a Mahanian navy asserting, by its presence, the access that Indonesian law sought to deny.
The other protesters reveal why the claim cut so deep. Australia, the only neighbour among them, saw the contested straits as its commercial lifelines to Asia and Europe — the Victorious was itself en route to Australia when the 1964 crisis erupted. Japan was the most exposed of all: the overwhelming bulk of its oil moved from the Persian Gulf through the Straits of Malacca and Singapore, Sunda, Lombok, and Makassar, and American analysts in the early 1970s assessed that an Indonesian restriction on passage would lay a hand on the Japanese economy’s jugular. Declassified American records show that Washington, too, understood precisely what was at stake. An 1973 CIA assessment concluded that Indonesia sought the right to deny use of the sea lanes crossing its archipelago. By 1974 the matter had escalated to personal correspondence between Presidents Nixon and Suharto.
This was sea denial in a second dimension — legal-diplomatic rather than kinetic — and it achieved what capital ships could not. That every major maritime power protested, and that one sent an aircraft carrier, is the measure of what the declaration threatened. Indonesia, without a blue-water navy, raised the legal and political cost of unrestricted access until the world’s strongest maritime powers accepted a new rule, balanced by archipelagic sea lanes passage. No other state has executed denial on that scale by legal means.
Indonesia’s geography provides the first dimension. Three of the world’s critical chokepoint systems — the Straits of Malacca and Singapore, Sunda, and Lombok–Ombai–Wetar — pass through or alongside its waters. Seventeen thousand islands form a natural defensive battlespace in which any intruding fleet faces Xerxes’ problem at Salamis: seas that turn numerical superiority into vulnerability.
The third dimension — affordable kinetic denial through missiles, drones, submarines, and mine warfare — is the one Indonesia is also developing. Ukraine and the Red Sea demonstrate how decisively that gap can now be closed, and how cheaply relative to a conventional fleet build-up.
Leverage for the Region
For most of the world’s maritime states, the strategic question of this century is not how to command the sea — they never will — but how to prevent the sea from being commanded against them. The Sea Denial Trap reframes their position. Geography, international law, and asymmetric technology are not consolation prizes for states without carriers; when deliberately combined, they form a strategy that has repeatedly defeated carrier groups.
The archipelagic and middle powers of the Indo-Pacific — Indonesia, the Philippines, Malaysia, Vietnam, Sri Lanka — hold more leverage than tonnage tables suggest. A coalition of archipelagic and coastal states defending and extending the UNCLOS regime they co-authored would be more durable than any unilateral posture — and more credible than any externally supplied security guarantee.
For great powers, the implications are sobering. Every projection of naval force into littoral Asia now runs through waters where the trap can be set — legally through coastal state rights under UNCLOS, geographically through straits and island chains, and kinetically through weapons any middle power can field. The era in which a superior fleet could have access at acceptable cost is closing. Mahan taught the world to count battleships. The century ahead will belong to those who count chokepoints, legal entitlements, and the price of admission.
Indonesia articulated this logic before anyone else — in 1957, in the language of law rather than firepower — and the protests of seven maritime powers, sustained for a quarter of a century, proved that the world’s naval fleets understood it. It is time the doctrine bore an archipelagic name.
About the Author
Arif Havas Oegroseno is the Vice Minister for Foreign Affairs of the Republic of Indonesia. He has been a negotiator of maritime boundary agreements and has written extensively on the law of the sea and the doctrine of the archipelagic state. He was the President of the 20th Meeting of States Parties to UNCLOS 1982. The views expressed are his own.
