International Straits

Introduction

International straits are naturally formed waterways connecting two parts of the sea and used for international navigation.

They are important because they often connect:

• two areas of the high seas or EEZs;
• an EEZ and another maritime area;
• major oceans and seas.

International straits create a balance between two competing interests:

Coastal States

→ Sovereignty over their territorial seas

International Community

→ Freedom of navigation and overflight through important international routes

The principal legal framework is Part III of UNCLOS, Articles 34–45.

The most important concept is:

Transit Passage

Transit passage gives ships and aircraft a right of continuous and expeditious passage through qualifying international straits.

Meaning of an International Strait

There is no single definition of “international strait” in UNCLOS.

The legal regime generally depends upon the geographical characteristics of the waterway and its use for international navigation.

A strait is particularly important when it:

• connects one part of the high seas or EEZ to another;
• is naturally formed;
• is used for international navigation.

Legal Basis

The principal provisions are:

• Article 34 → Legal status of waters forming straits
• Article 35 → Scope of the straits regime
• Article 36 → High seas/EEZ routes
• Article 37 → Application of transit passage
• Article 38 → Right of transit passage
• Article 39 → Duties of ships and aircraft
• Article 40 → Research and survey
• Article 41 → Sea lanes and traffic separation schemes
• Article 42 → Laws and regulations of bordering States
• Article 43 → Safety and pollution cooperation
• Article 44 → Duties of States bordering straits
• Article 45 → Innocent passage

Geographical Concept

A simple example is:

Sea A

↓

International Strait

↓

Sea B

The strait may pass through the territorial seas of one or more coastal States.

The fact that the waterway lies within territorial seas does not automatically mean that ordinary innocent passage is the only applicable regime.

Where the conditions of Part III are satisfied, transit passage applies.

What Is a Strait Used for International Navigation?

The modern UNCLOS regime is principally concerned with straits used for international navigation.

The key question is therefore not simply:

Is it geographically narrow?

The important question is also:

Does it fall within the legal categories covered by Part III and serve international navigation?

Article 37 – Core Provision

Article 37 provides that the transit-passage regime applies to straits used for international navigation between:

• one part of the high seas or an EEZ;
• and another part of the high seas or an EEZ.

This is the central category of international straits under UNCLOS.

Transit Passage

Article 38 UNCLOS

Transit passage means the exercise of:

freedom of navigation and overflight

solely for the purpose of:

continuous and expeditious transit through the strait.

This applies to:

• ships;
• aircraft.

Core Formula

International Strait → Transit Passage → Ships + Aircraft

This is one of the most important rules to remember.

Why Transit Passage Exists

International navigation routes can be vital for:

• international trade;
• naval movement;
• commercial shipping;
• aviation;
• global transportation.

If every coastal State could completely restrict movement through a strategically important strait, international navigation could be seriously disrupted.

Transit passage therefore protects international movement while preserving the sovereignty of the States bordering the strait.

Transit Passage vs Innocent Passage

This is the most important distinction in the topic.

Innocent Passage

• Primarily applies to ships.
• Passage must be innocent.
• Submarines must generally navigate on the surface.
• Aircraft do not enjoy a general right of innocent passage through territorial seas.

Transit Passage

• Applies to ships and aircraft.
• Passage must be continuous and expeditious.
• Submarines may navigate in their normal mode, including submerged.
• Cannot be suspended.

Memory Rule

Innocent Passage = Ships

Transit Passage = Ships + Aircraft

Submarines

This is a frequently tested point.

Innocent Passage

A submarine must generally:

Navigate on the surface + show its flag

Transit Passage

A submarine may:

Navigate in its normal mode

Therefore, submerged navigation is permitted during transit passage.

Aircraft

Aircraft do not have a general innocent-passage right through territorial seas.

However, aircraft are expressly protected by the transit-passage regime.

Thus:

Transit Passage = Navigation + Overflight

Continuous and Expeditious Passage

Transit passage is not a general right to stop and conduct unrelated activities.

Ships and aircraft must proceed:

Continuously

and

Expeditiously

through the strait.

Their passage must be connected with the purpose of transit.

Article 39 – Duties During Transit

Ships and aircraft exercising transit passage must:

• proceed without delay;
• refrain from threats or use of force inconsistent with the UN Charter;
• refrain from activities other than those incidental to their normal modes of continuous and expeditious transit;
• comply with other generally accepted international regulations concerning safety and pollution.

Normal Mode

Ships and aircraft must proceed in their normal mode of operation.

This is particularly significant for:

• submarines;
• aircraft;
• military vessels.

No Threat or Use of Force

A ship or aircraft exercising transit passage must refrain from:

• threat or use of force;
• activities contrary to the purposes and principles of the UN Charter.

Therefore, transit passage is not a licence for unlawful military action.

Research and Survey

Article 40

Foreign ships exercising transit passage cannot carry out:

• marine scientific research;
• hydrographic surveys

without prior authorisation from the States bordering the strait.

This is an important limitation on transit passage.

Article 41 – Sea Lanes

States bordering straits may designate:

• sea lanes;
• traffic separation schemes

where necessary to promote safe passage.

Such designations must conform to generally accepted international regulations.

International Maritime Organization

The designation of sea lanes and traffic separation schemes may involve cooperation with the International Maritime Organization (IMO) where required under UNCLOS.

Article 42 – Laws of Strait States

States bordering straits may adopt laws and regulations relating to transit passage concerning matters such as:

• safety of navigation;
• regulation of maritime traffic;
• pollution;
• fishing;
• loading and unloading;
• customs, fiscal, immigration and sanitary matters.

However, their laws must conform to UNCLOS.

Limits on Regulation

States bordering straits cannot:

• deny transit passage;
• hamper transit passage;
• discriminate among ships;
• effectively impair the right of transit passage.

Therefore:

Regulation ≠ Denial

A State can regulate transit, but cannot destroy the right itself.

Article 43 – Burden Sharing

User States and States bordering straits should cooperate through agreement:

• to establish necessary navigational and safety aids;
• to prevent, reduce and control pollution from ships.

This reflects the shared international importance of major straits.

Article 44 – Duties of Strait States

States bordering straits must not:

• hamper transit passage;
• suspend transit passage.

They must also give appropriate publicity to any danger to navigation or overflight of which they have knowledge.

Transit Passage Cannot Be Suspended

This is a major distinction from innocent passage.

Innocent Passage

May be suspended in limited circumstances under UNCLOS.

Transit Passage

Cannot be suspended.

This ensures the continuous operation of international navigation routes.

Article 45 – Innocent Passage in Certain Straits

Not every strait is governed by transit passage.

Article 45 preserves the regime of innocent passage in certain categories of straits.

These include:

Category 1

Straits excluded from the transit-passage regime under Article 38(1) because they are:

• between a part of the high seas or EEZ and the territorial sea of a foreign State.

Category 2

Straits formed by an island of a State bordering the strait and its mainland, where:

• there exists seaward of the island a route through the high seas or EEZ;
• the route is of similar convenience with respect to navigational and hydrographical characteristics.

Special Strait Regimes

UNCLOS does not replace every existing legal regime governing every strait.

Article 35(c)

Nothing in Part III affects the legal regime in straits where passage is regulated in whole or in part by:

• long-standing international conventions specifically relating to such straits.

This protects certain pre-existing treaty regimes.

Important Examples of Special Regimes

Examples often discussed include:

• Turkish Straits;
• Strait of Magellan.

Their legal regimes must be examined through their specific treaties and applicable international law rather than assuming that the general UNCLOS transit-passage regime automatically governs every aspect.

Strait of Hormuz

The Strait of Hormuz is a major international waterway connecting the:

Persian Gulf

with the:

Gulf of Oman

and ultimately the Indian Ocean.

Its importance comes from:

• international shipping;
• energy transportation;
• strategic navigation.

The legal debate concerning navigation through the Strait of Hormuz illustrates the importance of the transit-passage regime.

Strait of Malacca

The Strait of Malacca connects:

• the Indian Ocean region;
• the South China Sea and broader Pacific maritime routes.

It is one of the world’s major shipping routes.

Its international importance makes the rules of transit, navigation safety and pollution particularly significant.

Strait of Gibraltar

The Strait of Gibraltar connects:

• Atlantic Ocean;
• Mediterranean Sea.

It is an important example of a major international navigation route.

Bab-el-Mandeb

The Bab-el-Mandeb connects:

• Red Sea;
• Gulf of Aden.

It is strategically important for international shipping between the Indian Ocean and the Mediterranean through the Suez Canal route.

Danish Straits

The Danish Straits connect the:

North Sea/Baltic Sea system

and have historically been governed by special legal arrangements alongside the general development of the law of international straits.

Bosporus and Dardanelles

The Turkish Straits, comprising the:

• Bosporus;
• Sea of Marmara;
• Dardanelles;

have a distinctive treaty regime under the Montreux Convention of 1936.

Therefore, their legal treatment cannot simply be reduced to the general UNCLOS rules.

International Straits and Sovereignty

States bordering a strait may exercise sovereignty over their territorial seas.

However, where the transit-passage regime applies, that sovereignty is subject to the internationally protected right of transit passage.

Therefore:

Strait State → Sovereignty

but:

International Strait → Transit Passage

Sovereignty vs Passage

The central balance is:

Coastal State

→ sovereignty over territorial sea

International Community

→ transit passage

This is the foundation of Part III UNCLOS.

International Strait vs Territorial Sea

A strait may contain territorial waters, but the presence of territorial waters does not automatically determine the passage regime.

Where Part III applies:

Transit Passage takes priority as the applicable passage regime.

International Strait vs Archipelagic Sea Lanes

These are separate legal regimes.

International Strait

→ Transit Passage

→ Part III

Archipelagic Waters

→ Archipelagic Sea Lanes Passage

→ Part IV

Both may involve:

• ships;
• aircraft;
• continuous and expeditious passage;
• submerged submarine navigation.

But they apply in different geographical circumstances.

Comparison

Transit Passage	Archipelagic Sea Lanes Passage
Part III	Part IV
International straits	Archipelagic waters
Ships + aircraft	Ships + aircraft
Continuous and expeditious	Continuous and expeditious
Submarines may remain submerged	Submarines may remain submerged
Cannot be suspended	Cannot be freely suspended
Articles 37–44	Articles 53–54

International Strait vs Innocent Passage

Transit Passage	Innocent Passage
Part III	Mainly Part II
Ships + aircraft	Ships
Continuous and expeditious	Continuous and expeditious
Submarines may remain submerged	Submarines generally surface
Cannot be suspended	May be suspended under applicable rules
Wider navigation regime	More limited regime
Applies to qualifying international straits	General territorial-sea passage

International Strait vs High Seas

International Strait	High Seas
May lie within territorial seas	Outside national maritime zones
Coastal-State sovereignty may apply	No State sovereignty
Transit passage may apply	Freedom of high seas
Ships + aircraft	Navigation and other high-seas freedoms
Part III	Part VII

International Strait vs Contiguous Zone

The contiguous zone is an enforcement zone extending up to 24 nm from baselines.

An international strait is a geographical waterway whose passage regime depends on its characteristics and applicable law.

Therefore, the two concepts should not be confused.

International Strait vs Canal

This distinction is also important.

Natural Strait

Naturally formed waterway.

Canal

Artificially constructed waterway.

The legal regime of an artificial canal depends on its treaties and applicable international law.

An artificial canal does not automatically acquire the legal status of an international strait under Part III UNCLOS.

International Strait and Marine Pollution

Pollution from shipping is a major concern in international straits.

States bordering straits may adopt regulations consistent with UNCLOS concerning:

• pollution prevention;
• maritime safety;
• traffic separation.

International cooperation is particularly important because pollution can affect multiple States and marine ecosystems.

International Strait and Fisheries

States bordering a strait may regulate fisheries in accordance with UNCLOS and applicable international law.

However, fisheries regulations cannot be used as a disguised means of eliminating lawful transit passage.

International Strait and Environmental Protection

States bordering straits have legitimate interests in protecting:

• marine ecosystems;
• coastal environments;
• navigational safety.

However, environmental regulations must remain consistent with the transit-passage regime.

International Strait and Warships

Warships enjoy transit-passage rights where the relevant UNCLOS conditions are satisfied.

A coastal State cannot simply prohibit warships from transiting a qualifying international strait on the ground that they are military vessels.

The vessel must, however, comply with the duties imposed by Article 39.

International Strait and Submarines

This is a highly important examination point.

Territorial Sea – Innocent Passage

Submarine must surface.

International Strait – Transit Passage

Submarine may remain submerged.

Archipelagic Sea Lanes Passage

Submarine may remain submerged.

International Strait and Aircraft

Innocent Passage

No general right for aircraft.

Transit Passage

Aircraft have a right of overflight.

This is one of the strongest features of the transit-passage regime.

Important Case: Corfu Channel

Corfu Channel (United Kingdom v Albania)

This is the classic case on international straits.

The ICJ dealt with navigation through the Corfu Channel, including the rights of passage of warships.

The case is important for:

• international straits;
• passage rights;
• coastal-State responsibility;
• maritime safety;
• mines and navigational hazards.

The Court recognised the international character of the Corfu Channel and addressed the right of passage of ships through an international waterway.

Examination Importance

Corfu Channel = Classic case on international straits and passage.

Important Case: Strait of Corfu and Mines

The case also established important principles concerning a State’s duty regarding known dangers in waters under its control.

Albania was held responsible for failing to notify the United Kingdom of the minefield.

This illustrates the connection between:

Navigation

and

Safety obligations

Corfu Channel and UNCLOS

The Corfu Channel case was decided in 1949, before UNCLOS 1982.

Therefore, it should not be presented as an interpretation of Article 38 of UNCLOS.

Instead, it is a foundational case in the historical development of international straits and navigational rights.

Important Case: Nicaragua v Colombia

The maritime jurisprudence involving Nicaragua and Colombia is relevant to questions concerning maritime zones and navigation, although it is not the primary case on transit passage.

It can be used to discuss broader maritime entitlements.

Important Case: Qatar v Bahrain

The Qatar v Bahrain maritime delimitation case is relevant to questions concerning territorial seas, islands and maritime boundaries.

Again, it is not the principal authority on transit passage.

Importance of the Transit-Passage Regime

Transit passage protects:

• global commerce;
• international shipping;
• aviation;
• strategic navigation;
• access between maritime areas.

It prevents a coastal State from effectively closing an internationally important maritime route.

Limits on Transit Passage

Transit passage is not unrestricted.

Ships and aircraft must:

• proceed continuously;
• proceed expeditiously;
• refrain from threats/use of force inconsistent with the UN Charter;
• avoid unrelated activities;
• comply with relevant safety and pollution rules.

No Right to Conduct Research

A vessel cannot use transit passage as a pretext for:

• marine scientific research;
• hydrographic surveys.

Such activities require prior authorisation under Article 40.

No Right to Stop for Unrelated Activities

Transit passage is fundamentally a transit right.

The purpose is movement through the strait, not general use of the strait for unrelated activities.

Role of International Maritime Organisation

The IMO has an important practical role in:

• maritime safety;
• traffic separation schemes;
• navigational standards;
• pollution prevention.

The legal powers of the IMO should, however, be distinguished from the jurisdiction of the States bordering the strait.

Important Articles at a Glance

General Regime

Article 34 → Legal status

Article 35 → Exceptions

Article 36 → High seas/EEZ routes

Transit Passage

Article 37 → Applicability

Article 38 → Transit passage

Article 39 → Duties

Article 40 → Research and survey

Article 41 → Sea lanes

Article 42 → Laws and regulations

Article 43 → Cooperation

Article 44 → Duties of bordering States

Innocent Passage

Article 45 → Innocent passage in certain straits

Article 38 Memory Trick

“N-O”

N → Navigation

O → Overflight

Both are protected through:

Transit Passage

Article 39 Memory Trick

“C-N-N”

C → Continuous

N → No delay

N → No threat/use of force

Ships and aircraft must proceed continuously and expeditiously.

Article 44 Memory Trick

“Do Not Block”

Strait States:

Cannot hamper

Cannot suspend

transit passage.

Complete International Strait Flowchart

Naturally Formed Strait

↓

Used for International Navigation?

↓

Does Article 37 apply?

↓

YES

Transit Passage

↓

Ships + Aircraft

↓

Continuous + Expeditious

↓

Submarines may remain submerged

↓

Cannot be suspended

NO / Article 45 or Special Regime

↓

Applicable Innocent-Passage or Treaty Regime

Common Examination Mistakes

Mistake 1: International Strait Means International Waters

Incorrect.

A strait can contain the territorial sea of bordering States.

The important question is the applicable passage regime.

Mistake 2: Transit Passage Applies to Every Strait

Incorrect.

Articles 35, 36 and 45 contain important qualifications, and special treaty regimes may also apply.

Mistake 3: Transit Passage Is the Same as Innocent Passage

Incorrect.

Transit passage is broader and applies to both ships and aircraft.

Mistake 4: Aircraft Have Innocent Passage

Incorrect.

Aircraft are covered by the transit-passage regime, not ordinary innocent passage.

Mistake 5: Submarines Must Surface in Every Maritime Zone

Incorrect.

They may remain submerged during transit passage.

Mistake 6: Transit Passage Can Be Suspended

Incorrect.

Article 44 prohibits suspension.

Mistake 7: Coastal State Has No Sovereignty Over Strait

Incorrect.

The coastal State may exercise sovereignty over its territorial sea, subject to the applicable international passage regime.

Mistake 8: Transit Passage Allows Any Military Activity

Incorrect.

Ships and aircraft must comply with Article 39 and applicable international law.

Mistake 9: Research Is Automatically Allowed During Transit

Incorrect.

Article 40 requires prior authorisation for marine scientific research or hydrographic surveys.

Mistake 10: Every International Strait Is Governed Only by UNCLOS

Incorrect.

Article 35(c) protects certain special treaty regimes.

Quick Revision

• International straits → Part III UNCLOS.
• Main provisions → Articles 34–45.
• International strait generally involves a naturally formed waterway used for international navigation.
• Article 37 → transit-passage regime.
• Transit passage applies to qualifying straits connecting:
  • one part of high seas/EEZ;
  • with another part of high seas/EEZ.
• Article 38 → transit passage.
• Transit passage = freedom of:
  • navigation;
  • overflight.
• Ships + Aircraft.
• Passage must be:
  • continuous;
  • expeditious.
• Article 39 → duties during transit.
• No threats/use of force inconsistent with UN Charter.
• Ships and aircraft must proceed in their normal mode.
• Submarines may remain submerged.
• Article 40 → no research/survey without prior authorisation.
• Article 41 → sea lanes and traffic separation schemes.
• Article 42 → laws and regulations of bordering States.
• Coastal States cannot use regulations to destroy transit passage.
• Article 43 → cooperation for navigational aids and pollution prevention.
• Article 44 → transit passage cannot be hampered or suspended.
• Article 45 → innocent passage in certain straits.
• Some straits have special treaty regimes.
• Article 35(c) → preserves certain special conventions.
• International strait may lie within territorial seas.
• International strait ≠ international waters.
• Transit passage ≠ innocent passage.
• Transit passage ≠ archipelagic sea lanes passage.
• Transit passage is broader than innocent passage.
• Aircraft → transit passage.
• Submarines → submerged during transit passage.
• Key case → Corfu Channel.
• Important related maritime cases:
  • Nicaragua v Colombia;
  • Qatar v Bahrain.
• Major examples:
  • Strait of Hormuz;
  • Strait of Malacca;
  • Strait of Gibraltar;
  • Bab-el-Mandeb;
  • Turkish Straits.
• Special treaty regimes must be considered separately.
• Core formula:

International Strait → Transit Passage → Ships + Aircraft → Continuous + Expeditious → No Suspension

One-Line Memory Trick

International Straits

“38 – 39 – 40 – 44”

38 → Transit Passage

39 → Duties

40 → No Research/Survey Without Authorisation

44 → No Hampering or Suspension

And:

“Transit = Ships + Aircraft + Submerged Submarines”

Final Maritime-Zone Formula

Territorial Sea → International Strait → Transit Passage

Territorial Sea

→ Coastal-State sovereignty

↓

Qualifying International Strait

→ Sovereignty remains

→ Transit Passage

↓

Ships + Aircraft

↓

Continuous + Expeditious

↓

Submarines may remain submerged

↓

Transit passage cannot be suspended

Conclusion

International straits occupy a special position in the law of the sea because they bring together two important principles: coastal-State sovereignty and international freedom of navigation.

Under Part III of UNCLOS, Articles 34–45, qualifying straits used for international navigation are governed primarily by the regime of transit passage. Under Article 38, transit passage includes freedom of navigation and overflight solely for the purpose of continuous and expeditious transit.

The most important feature of transit passage is that it applies to:

Ships + Aircraft

This distinguishes it from ordinary innocent passage. Submarines exercising transit passage may also navigate in their normal mode, including while submerged.

However, transit passage is not unlimited. Under Article 39, ships and aircraft must proceed continuously and expeditiously and refrain from threats or use of force inconsistent with the UN Charter. Under Article 40, marine scientific research and hydrographic surveys require prior authorisation.

States bordering straits retain sovereignty and may adopt appropriate laws concerning navigation safety, pollution and related matters under Article 42. But they cannot use those powers to effectively destroy the right of transit passage.

The strongest protection is found in Article 44, which provides that States bordering straits shall not hamper transit passage and shall not suspend it.

Not every strait is governed by transit passage. Article 45 preserves innocent passage for certain straits, while Article 35(c) protects certain special treaty regimes.

The classic historical authority is Corfu Channel, which established important principles concerning international navigation through straits and the responsibility of States for known navigational dangers.

The entire topic can be remembered through:

“38 – 39 – 40 – 44”

38 → Transit Passage

39 → Duties

40 → Research/Sanctions

44 → No Hampering or Suspension

And the central formula:

International Strait = Transit Passage = Ships + Aircraft + Continuous & Expeditious Passage