Territorial Sea

Introduction

The territorial sea is the belt of coastal waters extending up to 12 nautical miles from the baseline of a coastal State.

Under the modern law of the sea, particularly UNCLOS 1982, the coastal State exercises sovereignty over its territorial sea.

This sovereignty extends to:

• the waters;
• the seabed;
• the subsoil;
• the airspace above the territorial sea.

However, territorial sovereignty is subject to important limitations, most importantly the right of innocent passage enjoyed by ships of all States.

The basic formula is:

Baseline → Up to 12 nautical miles → Territorial Sea → Coastal-State Sovereignty + Innocent Passage

Legal Basis

The principal legal framework is found in Part II of UNCLOS, particularly:

• Article 2 → Legal status of the territorial sea
• Article 3 → Breadth of the territorial sea
• Article 4 → Outer limit
• Articles 5–14 → Baselines
• Articles 15–32 → Passage through the territorial sea

Historical Development

The concept of territorial waters developed from the traditional idea that coastal States could exercise authority over a limited belt of sea adjacent to their coastline.

Historically, the three-mile rule became influential, partly associated with the range of coastal artillery.

However, State practice gradually expanded maritime claims.

The modern position is now codified in UNCLOS:

Maximum Territorial Sea

12 nautical miles

The 12-nautical-mile rule is widely accepted as the modern international standard.

Article 2 – Legal Status

Article 2 UNCLOS establishes the legal status of the territorial sea.

The sovereignty of a coastal State extends beyond its land territory and internal waters to:

• an adjacent belt of sea;
• the airspace over the sea;
• the seabed;
• the subsoil.

This belt constitutes the territorial sea.

However, the exercise of this sovereignty is subject to UNCLOS and other rules of international law, particularly the right of innocent passage.

Article 3 – Breadth of the Territorial Sea

Under Article 3, every State has the right to establish the breadth of its territorial sea up to a limit not exceeding:

12 nautical miles

measured from baselines determined in accordance with UNCLOS.

Therefore:

Territorial Sea = Maximum 12 nautical miles

Article 4 – Outer Limit

Under Article 4, the outer limit of the territorial sea is the line every point of which is at a distance from the nearest point of the baseline equal to the breadth of the territorial sea.

In simple terms:

Baseline

↓

12 nautical miles outward

↓

Outer Limit of Territorial Sea

Baseline

The territorial sea is measured from the baseline.

The baseline is therefore fundamental to determining its extent.

Normal Baseline

Under Article 5, the normal baseline is the low-water line along the coast as marked on officially recognised large-scale charts.

Straight Baselines

Under Article 7, straight baselines may be used in appropriate geographical circumstances, including:

• deeply indented coastlines;
• coastlines with a fringe of islands in their immediate vicinity.

Territorial Sea and Baseline Flowchart

Coast

↓

Baseline

↓

12 Nautical Miles

↓

Territorial Sea

Sovereignty Over Territorial Sea

The coastal State possesses sovereignty over the territorial sea.

This distinguishes the territorial sea from the EEZ.

Territorial Sea

Sovereignty

EEZ

Sovereign Rights + Specified Jurisdiction

Therefore, the territorial sea is legally closer to the State’s territory than the EEZ.

Scope of Sovereignty

Coastal-State sovereignty extends to:

Water

The coastal State exercises sovereignty over the waters of the territorial sea.

Seabed

The coastal State has sovereignty over the seabed.

Subsoil

The sovereignty extends to the subsoil.

Airspace

The sovereignty also extends to the airspace above the territorial sea.

Thus:

Territorial Sea

→ Water

→ Seabed

→ Subsoil

→ Airspace

Limit on Sovereignty

The sovereignty of the coastal State is not absolute.

The most important limitation is:

Right of Innocent Passage

Foreign ships enjoy the right of innocent passage through the territorial sea under UNCLOS.

Innocent Passage

The right of innocent passage is governed primarily by Articles 17–19.

Article 17

Ships of all States enjoy the right of innocent passage through the territorial sea.

This includes ships of:

• coastal States;
• other States;
• landlocked States.

Meaning of Passage

Under Article 18, passage means navigation through the territorial sea for the purpose of:

• traversing the territorial sea without entering internal waters; or
• proceeding to or from internal waters or a port facility.

Passage must be:

• continuous;
• expeditious.

Stopping and Anchoring

Passage may include stopping and anchoring where this is:

• incidental to ordinary navigation;
• rendered necessary by force majeure or distress;
• necessary to provide assistance to persons, ships or aircraft in danger or distress.

Therefore, innocent passage does not mean that a vessel must literally maintain constant forward movement in every circumstance.

When Passage Is Innocent

Under Article 19, passage is innocent so long as it is not prejudicial to the peace, good order or security of the coastal State.

This is the central test.

Activities Making Passage Non-Innocent

Article 19 identifies activities that may make passage non-innocent.

These include:

• threat or use of force against the sovereignty, territorial integrity or political independence of the coastal State;
• weapons exercises;
• intelligence collection prejudicial to defence or security;
• propaganda aimed at affecting defence or security;
• launching, landing or taking on board aircraft;
• launching, landing or taking on board military devices;
• loading or unloading goods, currency or persons contrary to applicable customs, fiscal, immigration or sanitary laws;
• wilful pollution;
• fishing;
• research or survey activities;
• interference with communications or other facilities;
• other activities not having a direct bearing on passage.

Innocent Passage Flowchart

Foreign Ship

↓

Enters Territorial Sea

↓

Passage

↓

Is Passage Continuous and Expeditious?

↓

Is It Non-Prejudicial to Peace, Good Order or Security?

↓

Yes → Innocent Passage

No → Non-Innocent Passage

Coastal-State Powers Concerning Innocent Passage

The coastal State may take appropriate measures to prevent passage through its territorial sea that is not innocent.

However, the coastal State must exercise its powers consistently with UNCLOS.

Laws and Regulations of Coastal State

Under Article 21, the coastal State may adopt laws and regulations relating to innocent passage concerning matters including:

• navigational safety;
• regulation of maritime traffic;
• protection of navigational aids;
• protection of cables and pipelines;
• conservation of living resources;
• prevention of infringement of fisheries laws;
• preservation of the environment;
• prevention of pollution;
• marine scientific research;
• customs;
• fiscal;
• immigration;
• sanitary matters.

Such laws must conform to UNCLOS and other rules of international law.

Prohibited Discrimination

The coastal State must not discriminate in form or in fact against ships of any particular State or against ships carrying cargoes to, from or on behalf of any State.

The regulatory power therefore cannot be used as arbitrary discrimination.

Sea Lanes and Traffic Separation Schemes

Under Article 22, the coastal State may, where necessary having regard to navigational safety, require foreign ships exercising innocent passage to use designated sea lanes and traffic separation schemes.

This is particularly important in:

• heavily trafficked waters;
• narrow approaches;
• environmentally sensitive areas.

Nuclear-Powered and Dangerous Ships

Under Article 23, foreign nuclear-powered ships and ships carrying nuclear or other inherently dangerous or noxious substances must carry documents and observe special precautionary measures established for such ships by international agreements.

Submarines

Under Article 20, submarines and other underwater vehicles must:

• navigate on the surface;
• show their flag

while exercising innocent passage through the territorial sea.

Warships

Warships have a special position under the UNCLOS regime.

The Convention recognises their right of innocent passage, while States have historically differed concerning whether prior authorisation or notification may be required.

UNCLOS itself does not expressly establish a general requirement that foreign warships obtain prior permission before exercising innocent passage.

Coastal-State Jurisdiction Over Foreign Ships

The coastal State’s criminal and civil jurisdiction over foreign ships in innocent passage is subject to specific UNCLOS limitations.

Criminal Jurisdiction

Under Article 27, the coastal State should not generally exercise criminal jurisdiction on board a foreign ship passing through the territorial sea to arrest a person or conduct an investigation in connection with a crime committed on board during passage, except in specified circumstances.

Exceptions include where:

• consequences of the crime extend to the coastal State;
• the crime is of a kind to disturb the peace of the country or good order of the territorial sea;
• assistance has been requested by the master or diplomatic/consular representative of the flag State;
• necessary measures are required for suppression of illicit traffic in narcotic drugs or psychotropic substances.

Civil Jurisdiction

Under Article 28, the coastal State should not generally stop or divert a foreign ship passing through the territorial sea for the purpose of exercising civil jurisdiction over a person on board.

Civil proceedings may nevertheless be taken against the ship in specified circumstances, particularly in relation to obligations or liabilities assumed by the ship during or for the purpose of its voyage through the coastal State’s waters.

Pollution

The coastal State may adopt and enforce appropriate rules concerning the prevention, reduction and control of pollution from ships, subject to UNCLOS and applicable international rules.

Marine environmental protection is therefore an important component of territorial-sea regulation.

Territorial Sea and Fisheries

The coastal State has sovereign control over fisheries in its territorial sea.

Foreign fishing vessels generally cannot fish in the territorial sea without authorisation.

Fishing during purported innocent passage may also cause the passage to cease being innocent under Article 19.

Territorial Sea and Marine Scientific Research

Marine scientific research by foreign vessels in the territorial sea is subject to the coastal State’s authority.

Research or survey activities can also make passage non-innocent under Article 19.

Territorial Sea and Security

The territorial sea is strategically important because it lies immediately adjacent to the coastal State’s land territory.

The coastal State may regulate activities affecting:

• national security;
• navigation;
• defence;
• communications;
• marine resources.

However, these powers must remain within the limits established by international law.

Territorial Sea and Navigation

The coastal State cannot treat the territorial sea simply as an area where all foreign navigation can be prohibited.

The right of innocent passage ensures a balance between:

Coastal-State Sovereignty

and

International Navigation

Territorial Sea and International Straits

Some territorial seas form part of straits used for international navigation.

In such cases, the special regime of transit passage may apply.

This is important because transit passage is broader than ordinary innocent passage.

Innocent Passage vs Transit Passage

Innocent Passage	Transit Passage
Territorial sea	Certain straits used for international navigation
Articles 17–19	Articles 37–44
Ships	Ships + aircraft
Must be innocent	Continuous and expeditious
No general right of overflight	Aircraft enjoy transit passage
Coastal-State regulatory powers	More limited interference with passage

Territorial Sea vs Internal Waters

This is one of the most important distinctions.

Territorial Sea	Internal Waters
Seaward of baseline	Landward of baseline
Up to 12 nm	No fixed nautical-mile limit
Sovereignty	Sovereignty
Innocent passage applies	No general right of innocent passage
Articles 2–32	Article 8

Memory Rule

Internal Waters → Sovereignty

Territorial Sea → Sovereignty + Innocent Passage

Territorial Sea vs Contiguous Zone

Territorial Sea	Contiguous Zone
Up to 12 nm	Up to 24 nm
Sovereignty	Limited enforcement control
Articles 2–32	Article 33
Innocent passage	No equivalent territorial sovereignty

Territorial Sea vs EEZ

Territorial Sea	EEZ
Up to 12 nm	Up to 200 nm
Sovereignty	Sovereign rights + specified jurisdiction
Airspace under sovereignty	No equivalent full coastal sovereignty
Innocent passage	Navigation freedoms
Articles 2–32	Part V

Territorial Sea and Landlocked States

Ships of landlocked States also enjoy the right of innocent passage.

The territorial sea is therefore not limited to navigation by neighbouring coastal States.

Territorial Sea and Freedom of Navigation

The law attempts to balance:

Coastal State

→ Sovereignty

with:

Foreign States

→ Innocent Passage

This balance is fundamental to the UNCLOS system.

Delimitation of Territorial Sea

Where two States have opposite or adjacent coasts, their territorial seas may overlap.

Article 15 provides the general rule.

The boundary is generally the median line, unless:

• otherwise agreed;
• historic title exists;
• special circumstances justify a different boundary.

Median Line

The median line is a line every point of which is equidistant from the nearest points on the baselines of the two States.

However, Article 15 recognises exceptions.

Therefore:

Median Line

is the general rule,

but

Historic Title / Special Circumstances

may justify another boundary.

Territorial Sea Delimitation Flowchart

Two Opposite/Adjacent Coasts

↓

Potential Overlap

↓

Article 15

↓

Median Line

↓

Check for Historic Title / Special Circumstances

↓

Final Territorial-Sea Boundary

Important Case: Anglo-Norwegian Fisheries

The Fisheries Case (United Kingdom v Norway) before the ICJ is an important authority concerning coastal baselines and the use of straight baselines.

The case examined Norway’s geographical circumstances and the method used to draw its baselines.

It remains significant for understanding:

• baselines;
• coastal geography;
• territorial waters.

Important Case: Qatar v Bahrain

The Maritime Delimitation and Territorial Questions between Qatar and Bahrain case involved complex questions concerning:

• territorial sovereignty;
• maritime delimitation;
• islands;
• maritime zones.

It demonstrates the interaction between territorial sovereignty and maritime entitlements.

Important Case: Nicaragua v Colombia

The ICJ’s Territorial and Maritime Dispute judgment involved:

• territorial sovereignty;
• islands;
• maritime zones;
• delimitation.

It is useful for understanding the relationship between territorial title and maritime entitlements.

Important Case: Corfu Channel

The Corfu Channel Case before the ICJ is important for navigation through territorial waters.

The case concerned the passage of British warships through the Corfu Channel and raised questions concerning:

• territorial sovereignty;
• innocent passage;
• international navigation.

It is a foundational case for the law governing navigation through territorial waters.

Territorial Sea and Warships

The Corfu Channel case is particularly relevant because it demonstrates that territorial sovereignty must be balanced with recognised international navigation rights.

The coastal State cannot simply exercise sovereignty without regard to international obligations.

Important Case: S.S. Lotus

The S.S. Lotus (France v Turkey) case before the PCIJ concerned a collision on the high seas rather than territorial-sea passage.

It remains important for the broader study of maritime jurisdiction and the relationship between:

• coastal-State jurisdiction;
• flag-State jurisdiction;
• international law.

Territorial Sea and Sovereign Immunity

Foreign warships and government ships operated for non-commercial purposes receive special immunity under applicable international law.

Article 32 UNCLOS preserves relevant immunities of warships and certain government ships.

Territorial Sea and Artificial Islands

Artificial islands do not generate their own territorial sea under UNCLOS.

The existence of an offshore artificial structure therefore does not automatically extend the territorial sea.

Territorial Sea and Rocks

A natural island can generate a territorial sea.

Even a rock that cannot sustain human habitation or economic life of its own may have a territorial sea, although Article 121(3) denies it an EEZ and continental shelf.

Territorial Sea and Airspace

The coastal State’s sovereignty over the territorial sea includes the airspace above it.

This distinguishes the territorial sea from the EEZ, where the coastal State does not possess equivalent sovereignty over the airspace.

Territorial Sea and Seabed

The coastal State has sovereignty over the seabed and subsoil beneath its territorial sea.

This gives it extensive authority concerning:

• seabed resources;
• installations;
• environmental protection.

Territorial Sea and Subsoil Resources

The coastal State may exploit natural resources of the seabed and subsoil in accordance with its sovereignty and applicable international law.

Territorial Sea and Cables

The laying of submarine cables and pipelines in the territorial sea is subject to the coastal State’s laws and regulations.

The coastal State may regulate such activities in accordance with UNCLOS.

Territorial Sea and Marine Environment

UNCLOS requires States to protect the marine environment.

Within the territorial sea, the coastal State can adopt regulations concerning:

• pollution;
• conservation;
• environmental protection.

Territorial Sea – Complete Legal Picture

Baseline

↓

12 Nautical Miles

↓

Territorial Sea

↓

Coastal-State Sovereignty

↓

Water + Seabed + Subsoil + Airspace

↓

Subject to UNCLOS

↓

Foreign Ships → Innocent Passage

Important UNCLOS Articles

Territorial Sea

Article 2 → Legal status and sovereignty

Article 3 → Breadth: 12 nautical miles

Article 4 → Outer limit

Article 5 → Normal baseline

Article 7 → Straight baselines

Article 8 → Internal waters

Article 10 → Bays

Article 15 → Territorial sea delimitation

Innocent Passage

Article 17 → Right of innocent passage

Article 18 → Meaning of passage

Article 19 → Meaning of innocent passage

Article 20 → Submarines

Article 21 → Coastal-State laws and regulations

Article 22 → Sea lanes and traffic separation schemes

Article 23 → Nuclear-powered and dangerous ships

Article 24 → Duties of coastal State

Article 25 → Rights of protection of coastal State

Jurisdiction

Article 26 → Charges levied upon foreign ships

Article 27 → Criminal jurisdiction

Article 28 → Civil jurisdiction

Article 29 → Definition of warship

Article 30 → Non-compliance by warships

Article 31 → Responsibility of flag State

Article 32 → Immunities of warships

Important Articles – Memory Table

Article	Subject
Article 2	Territorial-sea sovereignty
Article 3	12 nm
Article 4	Outer limit
Article 5	Normal baseline
Article 7	Straight baselines
Article 15	Delimitation
Article 17	Innocent passage
Article 18	Passage
Article 19	Innocent passage
Article 20	Submarines
Article 21	Coastal-State regulations
Article 22	Sea lanes
Article 24	Coastal-State duties
Article 25	Protective rights
Article 27	Criminal jurisdiction
Article 28	Civil jurisdiction
Article 32	Warship immunity

Quick Revision

• Territorial Sea is the maritime belt adjacent to the coast.
• Main legal framework → Part II UNCLOS.
• Article 2 → Legal status and sovereignty.
• Article 3 → Maximum 12 nautical miles.
• Measured from the baseline.
• Article 5 → Normal baseline.
• Normal baseline → low-water line.
• Article 7 → Straight baselines.
• Coastal State exercises sovereignty over the territorial sea.
• Sovereignty extends to:
  • water;
  • seabed;
  • subsoil;
  • airspace.
• Sovereignty is subject to UNCLOS and other international law.
• Foreign ships enjoy innocent passage.
• Article 17 → Right of innocent passage.
• Article 18 → Meaning of passage.
• Article 19 → Meaning of innocent passage.
• Passage must be continuous and expeditious.
• Passage is not innocent if prejudicial to the peace, good order or security of the coastal State.
• Fishing, research and certain security activities may make passage non-innocent.
• Article 20 → Submarines must navigate on the surface and show their flag during innocent passage.
• Coastal State may adopt navigation, environmental, customs, fiscal, immigration and sanitary regulations under Article 21.
• Coastal State may establish sea lanes and traffic separation schemes under Article 22.
• Foreign nuclear-powered and dangerous ships are subject to special documentation and precautionary rules under Article 23.
• Article 27 → Criminal jurisdiction.
• Article 28 → Civil jurisdiction.
• Article 32 → Warship immunities.
• Article 15 → Territorial-sea delimitation.
• General delimitation rule → median line, subject to historic title or special circumstances.
• Territorial sea differs from internal waters because of the right of innocent passage.
• Territorial sea differs from EEZ because the former involves sovereignty, while the latter involves sovereign rights and specified jurisdiction.
• Territorial sea differs from contiguous zone because the contiguous zone does not involve territorial sovereignty.
• Certain international straits are subject to the transit passage regime.
• Artificial islands do not generate their own territorial sea.
• Article 121 rocks may have territorial seas but not EEZs or continental shelves.
• Important cases:
  • Corfu Channel;
  • Anglo-Norwegian Fisheries;
  • Qatar v Bahrain;
  • Nicaragua v Colombia;
  • S.S. Lotus.

One-Line Memory Trick

Territorial Sea

“12 – S – I”

12 → 12 nautical miles

S → Sovereignty

I → Innocent Passage

Key Articles

2 → Sovereignty

3 → 12 nm

5 → Baseline

7 → Straight Baselines

15 → Delimitation

17 → Innocent Passage

18 → Passage

19 → Innocent

20 → Submarines

21 → Regulations

22 → Sea Lanes

27 → Criminal Jurisdiction

28 → Civil Jurisdiction

32 → Warship Immunity

Maritime-Zone Formula

Internal Waters → Sovereignty

Territorial Sea → Sovereignty + Innocent Passage

Contiguous Zone → Limited Enforcement

EEZ → Sovereign Rights

High Seas → Freedom

Conclusion

The territorial sea is one of the fundamental maritime zones recognised by international law. Under Article 3 of UNCLOS, a coastal State may establish a territorial sea extending up to 12 nautical miles from its baselines.

Under Article 2, the coastal State exercises sovereignty over the territorial sea, including its waters, seabed, subsoil and airspace. This makes the territorial sea fundamentally different from the EEZ, where the coastal State possesses sovereign rights and specified jurisdiction rather than full territorial sovereignty.

The most important limitation upon territorial sovereignty is the right of innocent passage. Under Article 17, ships of all States enjoy this right, while Articles 18 and 19 determine what constitutes passage and when passage ceases to be innocent. The coastal State may regulate navigation, environmental protection, fisheries and other matters under Article 21, but its regulatory powers must remain consistent with UNCLOS.

UNCLOS also establishes special rules concerning submarines, warships, criminal and civil jurisdiction, dangerous cargoes, sea lanes and maritime delimitation. Where territorial seas overlap, Article 15 generally refers to the median line, subject to historic title and special circumstances.

The territorial sea therefore represents a carefully balanced regime:

Coastal State Sovereignty

International Navigation Rights

↓

Territorial Sea under UNCLOS

For examination purposes, remember the essential formula:

Article 2 → Sovereignty

Article 3 → 12 nautical miles

Article 5 → Baseline

Article 15 → Delimitation

Article 17 → Innocent Passage

Article 19 → Meaning of Innocent Passage

Article 20 → Submarines

Article 21 → Coastal-State Regulations

Article 27 → Criminal Jurisdiction

Article 28 → Civil Jurisdiction

Article 32 → Warship Immunity