Innocent Passage Under International Law: UNCLOS Rules Explained
Introduction
Innocent passage is the right of ships of all States to navigate through another State’s territorial sea under the conditions established by the United Nations Convention on the Law of the Sea (UNCLOS). Article 17 recognizes the right, Article 18 defines what constitutes “passage,” and Article 19 determines when that passage remains innocent. Navigation must ordinarily be continuous and expeditious, and passage is innocent so long as it is not prejudicial to the peace, good order, or security of the coastal State (United Nations, 1982, arts. 17–19).
The right operates within waters that remain subject to coastal-State sovereignty. Article 2 extends that sovereignty over the territorial sea, the airspace above it, and its bed and subsoil, while making its exercise subject to UNCLOS and other rules of international law. Coastal States may regulate foreign ships in the fields specified by the Convention, but they may not impose requirements that have the practical effect of denying or impairing innocent passage (United Nations, 1982, arts. 2, 21 and 24). The regime limits the exercise of territorial authority without transforming the territorial sea into an area of unrestricted freedom of navigation.
Article 19 focuses on the conduct of a foreign ship while it is passing through the territorial sea. Threats or uses of force, weapons exercises, intelligence collection, fishing, research or survey activities, willful and serious pollution contrary to UNCLOS, and activities without a direct bearing on passage are among the acts that may render passage non-innocent. Article 25 allows the coastal State to take necessary steps to prevent passage that is not innocent and, under stricter conditions, to suspend innocent passage temporarily in specified areas for security reasons. That suspension power does not apply everywhere: Article 45 expressly prohibits suspension in certain straits where the innocent-passage regime governs (United Nations, 1982, arts. 19, 25 and 45).
Warships raise a more contested question. UNCLOS places Article 17 within rules applicable to all ships and separately regulates warships in Articles 29–32, including their immunity, non-compliance, and flag-State responsibility. The Convention does not expressly resolve whether coastal States may require prior notification or authorization for warship passage in every territorial sea. In Corfu Channel, the International Court of Justice held that, in peacetime, States have a right under international custom to send warships through straits used for international navigation between two parts of the high seas without prior authorization, provided that the passage is innocent (ICJ, 1949, p. 28). The scope of that judgment, the practice of States concerning warship authorization, and the distinct regime of transit passage in international straits remain central to understanding the limits of coastal-State control under the modern law of the sea.
1. Innocent Passage Within Coastal-State Sovereignty
The territorial sea is subject to the sovereignty of the coastal State. Article 2 of the United Nations Convention on the Law of the Sea (UNCLOS) extends that sovereignty beyond the State’s land territory and internal waters to the adjacent territorial sea, including the airspace above it and its bed and subsoil. Under Article 3, a coastal State may establish a territorial sea up to 12 nautical miles from the baselines prescribed by the Convention. Sovereignty over this zone is nevertheless exercised subject to UNCLOS and other rules of international law (United Nations, 1982, arts. 2–3).
Innocent passage is one of the principal qualifications on the coastal State’s exercise of that sovereignty. Article 17 provides that, subject to UNCLOS, ships of all States, whether coastal or land-locked, enjoy the right of innocent passage through the territorial sea. The Convention speaks in terms of a right enjoyed by foreign ships rather than a permission that the coastal State may ordinarily grant or withhold at its discretion (United Nations, 1982, art. 17).
The existence of that right does not deprive the territorial sea of its sovereign character. Foreign vessels remain subject to the conditions governing passage and to coastal-State laws adopted within the limits permitted by UNCLOS. The legal arrangement is one of concurrent rights and powers: the coastal State retains territorial authority, while international law restricts the ways in which that authority may be exercised against ships engaged in qualifying passage.
The applicable regime changes across maritime zones. Waters on the landward side of the territorial-sea baseline are generally internal waters and do not carry a general right of innocent passage. Article 8(2) creates a specific exception where the use of straight baselines encloses waters that had not previously been considered internal, preserving innocent passage through those waters. Beyond areas under coastal sovereignty, navigation on the high seas rests on the freedom of navigation recognized in Article 87 rather than on innocent passage (United Nations, 1982, arts. 8 and 87). The doctrine is distinctive because it protects foreign navigation within waters that remain part of the coastal State’s territorial domain.
2. What Counts as Passage Under Article 18
The legal inquiry does not begin with innocence. A vessel must first be engaged in “passage” within Article 18 before Article 19 determines whether that passage is innocent. The two provisions perform different functions, and collapsing them into a single test can obscure the structure of the Convention.
Article 18 defines passage as navigation through the territorial sea for specified purposes. It includes traversing that sea without entering internal waters or calling at a roadstead or port facility outside internal waters. It also covers navigation undertaken to proceed to or from internal waters, or to or from such a roadstead or port facility (United Nations, 1982, art. 18(1)).
A vessel may consequently fail to satisfy Article 18 even where none of the activities listed in Article 19(2) can readily be identified. If its presence in the territorial sea no longer amounts to navigation for one of the purposes recognized by Article 18, the basis for invoking innocent passage falls away at an earlier stage. A ship can equally satisfy Article 18 because it is genuinely in passage and yet lose the protection of innocence because of its conduct under Article 19.
2.1 Continuous and Expeditious Navigation
Article 18(2) requires passage to be continuous and expeditious. The requirement reflects the navigational purpose of the right: territorial waters may be used for passage, but the Convention does not confer a general entitlement to remain there indefinitely or to use them as an operating area for activities unrelated to transit.
Neither “continuous” nor “expeditious” imposes a fixed speed or requires every ship to follow the mathematically shortest course. UNCLOS specifies no such rule. Weather, navigational hazards, traffic conditions, vessel characteristics, prescribed sea lanes, collision-avoidance requirements, and other circumstances may legitimately affect both route and speed.
Prolonged stationary presence, repeated movement within a confined area, or substantial deviation from an apparent transit route may raise a different question when no navigational explanation exists. Such conduct is not automatically excluded by a numerical time limit, since Article 18 contains none. Its legal significance depends on whether the vessel remains engaged in genuine passage and whether any interruption can be justified under Article 18(2) (Tanaka, 2015).
Article 18 and Article 19 may nevertheless overlap in practice. A ship lingering to conduct a survey, for example, may raise doubts about whether its movement remains continuous and expeditious while also engaging Article 19(2)(j), which specifically identifies research or survey activities as prejudicial to innocence. The analytical questions remain separate even when the same facts are relevant to both.
2.2 Stopping, Anchoring, Distress, and Assistance
Continuous passage does not require uninterrupted movement. Article 18(2) expressly recognizes stopping and anchoring where they are incidental to ordinary navigation. An interruption reasonably connected with the safe conduct of the voyage does not cease to be passage merely because the vessel temporarily stops moving.
UNCLOS also protects interruptions rendered necessary by force majeure or distress. The same provision covers stopping or anchoring undertaken to assist persons, ships, or aircraft in danger or distress (United Nations, 1982, art. 18(2)). These exceptions prevent the continuity requirement from operating in a manner inconsistent with navigational necessity or emergency assistance.
The reason for the interruption is central to its legal characterization. An anchorage used as a base for activities unrelated to navigation cannot acquire the protection of Article 18 merely because the vessel remains at anchor. Conversely, a genuine emergency or navigational necessity is not converted into unlawful lingering simply because the interruption lasts longer than an ordinary transit would have required.
3. When Passage Ceases to Be Innocent
Once the requirements of Article 18 are satisfied, Article 19 determines whether the passage is innocent. Paragraph 1 states the general rule: passage remains innocent so long as it is not prejudicial to the peace, good order, or security of the coastal State. It must also take place in conformity with UNCLOS and other rules of international law (United Nations, 1982, art. 19(1)).
The general formulation does not leave the concept entirely to coastal-State discretion. Article 19(2) identifies a series of activities that render passage prejudicial when a foreign ship engages in them within the territorial sea. The treaty text directs attention largely toward conduct during passage rather than toward the nationality or political identity of the vessel.
That distinction is especially relevant to military shipping. Warship status does not depend on whether the ship is actually carrying weapons; Article 29 defines a warship through its State affiliation, external marks, command, and crew discipline. Nor does Article 19 treat warship status itself as equivalent to exercising weapons, collecting security-sensitive information, or conducting another listed activity. The legality of passage must be assessed through the rules that govern the vessel and its conduct.
Some cases remain difficult despite the specificity of Article 19(2). Several categories employ terms capable of disagreement, and the relationship between the general standard in paragraph 1 and the activities listed in paragraph 2 is itself contested. Innocence is consequently a legal characterization of particular passage, not merely a label attached to a class of vessels.
3.1 Article 19 and the Prohibited Activities
The first group of prohibited activities concerns force and military security. Article 19(2)(a) covers a threat or use of force against the sovereignty, territorial integrity, or political independence of the coastal State, as well as force used in another manner contrary to the principles of international law embodied in the UN Charter. Exercises or practice with weapons of any kind are addressed separately in Article 19(2)(b) (United Nations, 1982, art. 19(2)(a)–(b)).
Security-related information and influence operations form another category. Passage is non-innocent where the ship engages in an act aimed at collecting information to the prejudice of the coastal State’s defense or security. Article 19 also covers propaganda aimed at affecting the defense or security of the coastal State. The wording is narrower than a prohibition on every collection of navigational information or every communication by a foreign vessel; the prescribed security-related purpose or effect is part of the treaty standard (United Nations, 1982, art. 19(2)(c)–(d); Butler, 1987).
Operational activities involving aircraft or military devices are specifically regulated. Launching, landing, or taking on board an aircraft, or doing the same with a military device, renders passage prejudicial under Article 19(2)(e) and (f). The provision regulates the activity itself. The mere presence aboard a ship of an aircraft, weapon system, or other military equipment is not identified in these paragraphs as an independent basis for non-innocence.
Other paragraphs protect coastal regulatory, economic, and environmental interests. The loading or unloading of commodities, currency, or persons contrary to the coastal State’s customs, fiscal, immigration, or sanitary laws is included, as are fishing and research or survey activities. Article 19(2)(h) uses a deliberately qualified formulation for pollution, referring to an act of “willful and serious pollution” contrary to UNCLOS. Pollution that does not meet that standard may still engage other provisions of the Convention without necessarily falling within Article 19(2)(h).
The catalogue also includes interference with communication systems or other facilities or installations of the coastal State. Its final paragraph covers “any other activity not having a direct bearing on passage” (United Nations, 1982, art. 19(2)(k)–(l)). Article 19(2) does not identify foreign ownership, nationality, armament, destination, or politically sensitive cargo, standing alone, as separate prohibited activities. Whether other circumstances can nonetheless affect the general test under Article 19(1) belongs to a separate interpretive question.
3.2 Does Article 19(2) Exhaust the Test?
The relationship between the two paragraphs of Article 19 has generated different readings. One approach treats paragraph 2 as the operative catalogue of activities capable of making passage non-innocent, with paragraph (l) serving as a broad residual category for other activities lacking a direct connection with passage. This interpretation seeks to constrain unilateral coastal-State determinations by tying non-innocence to identifiable conduct.
The United States and Soviet Union adopted that position expressly in their 1989 Joint Statement and attached Uniform Interpretation of Rules of International Law Governing Innocent Passage. They regarded Article 19(2) as exhaustive and stated that a ship not engaging in one of the activities described there was in innocent passage (United States and USSR, 1989). The instrument is relevant State practice and carries particular significance because both parties were major naval powers, but it was a bilateral agreement and does not bind third States.
A different reading gives Article 19(1) an independent role. On this view, the general reference to prejudice to the peace, good order, or security of the coastal State is not wholly exhausted by paragraph 2. The breadth of paragraph 2(l) complicates that argument, since activities unrelated to passage can already be captured by the residual clause, yet academic commentary has continued to identify room for disagreement about how the two paragraphs interact (Tanaka, 2015).
Non-innocence should also be distinguished from violation of another rule governing passage. Article 21 permits the coastal State to adopt laws and regulations in specified fields, and Article 21(4) requires foreign ships exercising innocent passage to comply with applicable coastal laws adopted in conformity with UNCLOS and with generally accepted international regulations relating to collision prevention. Some violations may coincide with Article 19, particularly where paragraph 2 expressly incorporates coastal customs, fiscal, immigration, or sanitary laws. It does not follow that every regulatory breach automatically resolves the separate question whether passage has become non-innocent.
4. Warships, Permission, and Sovereign Immunity
Warship passage remains one of the more contested questions within the territorial-sea regime. UNCLOS contains substantial textual support for applying innocent passage to warships, yet it does not state in a single express provision that foreign warships may enter every territorial sea without prior notification or authorization. State practice has not eliminated the resulting disagreement.
Two separate questions are sometimes conflated. The first concerns whether warships fall within the category of ships capable of exercising innocent passage. The second asks whether a coastal State may impose prior notification or authorization as a condition for such passage. Acceptance of the first proposition does not by itself resolve every dispute surrounding the second.
Enforcement presents another problem because warships enjoy sovereign immunity. They remain subject to substantive rules governing passage, but UNCLOS does not treat them in the same manner as private merchant vessels when those rules are breached. Articles 29–32 address warship status, non-compliance, flag-State responsibility, and immunity within the Convention’s territorial-sea regime (United Nations, 1982, arts. 29–32).
4.1 Do Warships Have a Right of Innocent Passage?
The treaty argument begins with Article 17. It appears in Subsection A of UNCLOS Part II, Section 3, entitled “Rules Applicable to All Ships,” and grants ships of all States the right of innocent passage. No language in Article 17 excludes ships because they are operated by a navy.
The Convention later addresses warships expressly. Article 29 supplies a definition, Article 30 establishes a response to certain non-compliance, Article 31 regulates flag-State responsibility, and Article 32 preserves immunities. Reading those provisions alongside Article 17 provides substantial textual support for the proposition that warships can fall within the innocent-passage regime.
Article 19 is consistent with that reading. Its prohibited activities include weapons exercises, security-related information gathering, and operations involving aircraft or military devices. Those rules are capable of regulating military conduct during passage without treating the military identity of a vessel as sufficient, by itself, to make the passage non-innocent.
The 1989 United States–Soviet Joint Statement took a particularly broad position. Its attached Uniform Interpretation stated that the right extended to all ships, including warships, irrespective of cargo, armament, or means of propulsion, and that neither prior notification nor authorization was required (United States and USSR, 1989). The agreement established a common interpretation between those two States; it did not create treaty obligations for the international community as a whole.
Practice outside that bilateral arrangement has not been uniform. Some coastal States have asserted prior-notification or prior-authorization requirements for foreign warships, while maritime powers have objected that such conditions are incompatible with the right recognized by UNCLOS (Tanaka, 2015). Notification and authorization also carry different legal implications: notification communicates an intended passage, whereas authorization makes passage dependent on affirmative coastal-State consent. The compatibility of such requirements with UNCLOS remains disputed rather than conclusively resolved by the treaty text alone.
4.2 Corfu Channel and Prior Authorization
The principal judicial authority predates UNCLOS. In the Corfu Channel case, the International Court of Justice considered British naval passage through the North Corfu Channel, part of which lay within Albanian territorial waters. Albania had asserted during the preceding diplomatic exchanges that foreign warships and merchant vessels could not pass through its territorial waters without prior notification and permission (ICJ, 1949).
The Court addressed a narrower legal question. It held that international custom recognized, in time of peace, a right of States to send warships through straits used for international navigation between two parts of the high seas without the previous authorization of the coastal State, provided that the passage was innocent. In the absence of a contrary convention, a coastal State could not prohibit such passage through a qualifying strait in peacetime (ICJ, 1949, p. 28).
Whether the British passage of 22 October 1946 was innocent depended on its manner of execution. The Court considered the number and formation of the ships, their armament and orders, and the fact that their crews were at action stations. Against the background of an earlier incident in which Albanian coastal batteries had fired toward British vessels, the Court did not regard those precautions as sufficient to make the passage a violation of Albanian sovereignty (ICJ, 1949, pp. 29–30).
The later British minesweeping operation stood on a different legal footing. It was not treated as an exercise of innocent passage, and the Court rejected the United Kingdom’s asserted grounds for conducting the operation in Albanian territorial waters without Albania’s consent. The operation violated Albanian sovereignty (ICJ, 1949, p. 35). The contrast illustrates why the legal character of naval activity cannot be inferred solely from the identity of the vessels involved.
Corfu Channel does not establish a general holding that resolves warship passage through every territorial sea. The customary rule articulated by the Court concerned straits used for international navigation, and the judgment did not decide the broader status of foreign warships in ordinary territorial waters outside such a strait. Nor did its formulation of the customary rule settle every possible prior-notification regime. The case remains foundational, but its authority is strongest when confined to the legal question the Court actually decided.
4.3 Immunity, Non-Compliance, and the Order to Leave
Warship status under UNCLOS does not depend on armament. Article 29 defines a warship as a ship belonging to the armed forces of a State, bearing the external marks distinguishing ships of its nationality, commanded by a duly commissioned officer whose name appears in the appropriate service list or equivalent, and manned by a crew under regular armed-forces discipline (United Nations, 1982, art. 29). The definition concerns the vessel’s governmental and military status rather than the weapons it carries.
Sovereign immunity does not release such a vessel from the substantive law of passage. Article 30 applies where a warship fails to comply with coastal-State laws and regulations concerning passage through the territorial sea and disregards a request for compliance. In those circumstances, the coastal State may require the warship to leave the territorial sea immediately (United Nations, 1982, art. 30).
Article 31 addresses the consequences at the inter-State level. The flag State bears international responsibility for loss or damage to the coastal State resulting from non-compliance by a warship or another government ship operated for non-commercial purposes with coastal laws concerning passage, with UNCLOS, or with other rules of international law. The provision establishes State responsibility; it does not itself create a power to arrest or attach the foreign vessel.
Article 32 preserves the immunities of warships and other government ships operated for non-commercial purposes, subject to the relevant provisions of the innocent-passage regime. The combination of Articles 30–32 means that substantive obligations and immunity coexist. A warship can breach rules governing passage without becoming assimilated to a private vessel for purposes of coastal enforcement.
UNCLOS is less explicit about what follows if a warship refuses an order to depart. Article 30 creates the right to require immediate departure but does not set out a comprehensive catalogue of coercive measures for enforcing that demand. A general power to board, arrest, detain, or seize the warship cannot simply be inferred from Article 30 in disregard of sovereign immunity (Agyebeng, 2006; Tanaka, 2015).
Any coercive response beyond the mechanisms specified by UNCLOS would require assessment under the other applicable rules of international law. A resort to force, in particular, cannot be treated as an automatic consequence of Article 30; its legality would depend on a separate legal basis and the rules governing State immunity and the threat or use of force. The Convention resolves part of the problem by imposing compliance obligations, allowing an order to leave, preserving immunity, and assigning responsibility to the flag State, but it does not remove every enforcement difficulty created by a non-compliant warship.
5. Coastal-State Regulation of Innocent Passage
Innocent passage does not displace coastal-State jurisdiction over the territorial sea. Sovereignty remains the legal starting point, but UNCLOS regulates how that sovereignty may be exercised against foreign ships in passage. Articles 21–24 define substantial legislative powers while preventing domestic regulation from being used to nullify the navigational right recognized in Article 17.
Article 21 permits coastal legislation only in specified fields and requires such laws to conform to UNCLOS and other rules of international law. Foreign ships exercising innocent passage must comply with laws validly adopted under the Convention, as well as with generally accepted international regulations concerning the prevention of collisions at sea (United Nations, 1982, art. 21).
The resulting regime does not eliminate coastal regulation; it constrains its purpose and effect. A State may protect navigational safety, environmental interests, infrastructure, living resources, and border-control interests within the areas specified by UNCLOS. It may not convert those powers into a general licensing system that effectively replaces the international right of passage with permission dependent on coastal discretion.
Certain vessels are subject to additional rules because of their operation or the risks associated with them. UNCLOS deals expressly with submarines, traffic-routing measures, nuclear-powered ships, and vessels carrying dangerous substances. These provisions regulate the conditions of navigation without treating such ships as automatically incapable of exercising innocent passage.
5.1 Articles 21–23 and Conditions on Passage
Article 21(1) authorizes laws and regulations concerning the safety of navigation and maritime traffic; the protection of navigational aids, facilities, installations, cables, and pipelines; conservation of living resources and enforcement of fisheries laws; environmental protection and pollution control; marine scientific research and hydrographic surveys; and the prevention of infringements of customs, fiscal, immigration, and sanitary laws (United Nations, 1982, art. 21(1)).
That legislative competence has a significant technical limit. Coastal laws concerning innocent passage may not apply to the design, construction, manning, or equipment of foreign ships unless they give effect to generally accepted international rules or standards. The coastal State must also give due publicity to its applicable laws and regulations (United Nations, 1982, art. 21(2)–(3)).
Article 22 permits more specific control over routing. Where necessary, having regard to navigational safety, the coastal State may require foreign ships in innocent passage to use designated sea lanes or traffic separation schemes. Tankers, nuclear-powered ships, and vessels carrying nuclear or other inherently dangerous or noxious substances may in particular be required to confine their passage to such routes. In designating them, the coastal State must consider recommendations of the competent international organization, channels customarily used for international navigation, the characteristics of particular ships and channels, and traffic density (United Nations, 1982, art. 22).
Article 23 deals with nuclear-powered ships and vessels carrying nuclear or other inherently dangerous or noxious substances. When exercising innocent passage, these ships must carry the prescribed documents and observe special precautionary measures established for them by international agreements. UNCLOS does not provide that nuclear propulsion or hazardous cargo alone makes passage non-innocent. The Convention instead subjects such navigation to specific precautionary requirements.
Where the innocent-passage regime governs, Article 20 requires submarines and other underwater vehicles in the territorial sea to navigate on the surface and show their flag. Submerged navigation in those circumstances breaches Article 20. A separate interpretive question is whether that breach, without more, necessarily makes the passage non-innocent under Article 19. Academic commentary has divided on that issue because submerged navigation is not separately enumerated among the activities in Article 19(2) (Agyebeng, 2006; Tanaka, 2015).
5.2 Article 24 and the Limits of Regulation
Article 24 places direct limits on coastal-State authority. A coastal State must not hamper the innocent passage of foreign ships through its territorial sea except in accordance with UNCLOS. The restriction applies when the State implements the Convention and when it applies domestic laws adopted consistently with it (United Nations, 1982, art. 24(1)).
Two forms of interference are expressly prohibited. The coastal State may not impose requirements that have the practical effect of denying or impairing the right of innocent passage. It may not discriminate, formally or in practice, against the ships of any State or against vessels carrying cargoes to, from, or on behalf of a particular State (United Nations, 1982, art. 24(1)(a)–(b)).
Article 24 does not mean that every inconvenience associated with lawful regulation amounts to prohibited hampering. Routing requirements, collision-prevention rules, and other measures expressly contemplated by UNCLOS may affect how a ship passes through the territorial sea. Their legality depends on whether they remain within the authority granted by the Convention and do not produce the prohibited effect of denying or impairing the right.
The coastal State also has an informational duty. Article 24(2) requires appropriate publicity for dangers to navigation within the territorial sea of which the State has knowledge. The obligation reflects the same legal structure as the wider passage regime: sovereignty carries regulatory authority, but it also entails duties toward ships exercising rights recognized by international law.
Financial measures are constrained separately by Article 26. No charge may be imposed on a foreign ship merely because it passes through the territorial sea. Charges may be levied only for specific services actually rendered to the ship, and they must be imposed without discrimination (United Nations, 1982, art. 26). Innocent passage cannot be converted into a general toll-bearing privilege.
6. Coastal-State Action Against Non-Innocent Passage
Articles 21–24 regulate ships whose passage may remain innocent. Article 25 addresses protective measures when passage is not innocent or when conditions governing admission to internal waters or certain port facilities are at risk of being breached. The distinction separates ordinary regulation from intervention directed at conduct falling outside the protection of Article 19.
Under Article 25(1), the coastal State may take the necessary steps in its territorial sea to prevent passage that is not innocent. UNCLOS does not supply an exhaustive catalogue of permissible measures, and the phrase does not create an unrestricted enforcement power. Any action must remain connected to the non-innocent character of the passage and comply with other applicable rules of international law.
Article 25(2) concerns a different situation. Where ships are proceeding to internal waters or calling at a port facility outside internal waters, the coastal State may take necessary steps to prevent breaches of the conditions governing admission. This authority derives from the conditions attached to entry rather than from a general conclusion that lateral navigation through the territorial sea is non-innocent.
6.1 Necessary Steps Under Article 25(1)
The expression “necessary steps” links the coastal response to a legally identified threat to the innocent-passage regime. Article 25(1) does not authorize exclusion merely because the coastal State distrusts the vessel, disagrees with its flag State, or regards its voyage as politically unwelcome. A measure must respond to passage that can properly be characterized as non-innocent.
The provision is preventive in its wording, but UNCLOS does not prescribe a specific evidentiary threshold for action taken before prohibited conduct has run its course. Intervention cannot rest on speculation alone. There must be a sufficient factual and legal basis for treating the passage as non-innocent and for concluding that the measure adopted is necessary to prevent or bring that passage to an end.
Vessel characteristics may inform the factual context without independently determining the legal result. Foreign nationality, armament, sensitive cargo, military capability, or hostile political relations do not, by themselves, constitute any of the activities listed in Article 19(2). A warship capable of conducting surveillance or launching aircraft is not engaged in non-innocent passage merely because it possesses those capabilities; the relevant inquiry concerns what it is actually doing during passage.
The nature of the permissible response also depends on the ship involved. Directions concerning navigation or demands to cease a prohibited activity raise different legal questions from boarding, detention, seizure, or the use of force. Warships and other immune State vessels remain subject to the special rules in Articles 30–32, while coercive measures involving force engage rules extending beyond the innocent-passage provisions themselves.
6.2 Violation of Law and Loss of Innocence
A violation of a coastal-State regulation does not invariably answer whether passage has ceased to be innocent. Article 21(4) requires foreign ships exercising innocent passage to comply with applicable laws adopted consistently with UNCLOS. Article 19 uses a separate test to determine when passage is prejudicial to the peace, good order, or security of the coastal State.
Some violations fall expressly within both regimes. Article 19(2)(g), for example, treats the loading or unloading of commodities, currency, or persons contrary to coastal customs, fiscal, immigration, or sanitary laws as prejudicial to innocence. Other breaches of Article 21 regulations are not incorporated into Article 19 with the same direct wording. The consequences must be determined from the particular rule violated and the circumstances of the passage rather than from a general presumption that every breach extinguishes the right (Noyes, 2015).
The enforcement position for merchant ships is addressed more specifically in Articles 27 and 28. Article 27 generally restricts the exercise of coastal criminal enforcement jurisdiction on board a foreign ship merely passing through the territorial sea, while providing exceptions where, among other circumstances, the consequences of the crime extend to the coastal State or the crime disturbs the peace of the country or the good order of the territorial sea. It also contains distinct rules for vessels that have left internal waters (United Nations, 1982, art. 27).
Article 28 limits coastal interference for civil purposes. A passing foreign ship should not be stopped or diverted solely to exercise civil jurisdiction in relation to a person on board, and execution against or arrest of the ship is restricted, subject to the qualifications stated in paragraphs 2 and 3. These provisions differ markedly from the immunity-based rules applicable to warships. Loss of innocent status does not erase the legal consequences attached to the vessel’s classification.
7. Suspension of Innocent Passage
Suspension under Article 25(3) is distinct from action against an individual ship engaged in non-innocent passage. It temporarily prevents the exercise of otherwise lawful innocent passage within a defined area. The measure is directed at a geographic space and security need, rather than at misconduct by a particular vessel.
Because suspension interferes with navigation that would otherwise be protected, UNCLOS surrounds the power with specific conditions. It cannot operate as a general authority to close territorial waters for an indefinite period or to exclude foreign shipping for reasons unrelated to the security standard prescribed by the Convention.
The distinction between Article 25(1) and Article 25(3) is central. Paragraph 1 concerns passage that is already non-innocent. Paragraph 3 allows a temporary interruption of innocent passage itself, but only when every condition attached to that exceptional power is satisfied.
7.1 Conditions for Suspension Under Article 25(3)
Suspension must be temporary and confined to specified areas of the territorial sea. UNCLOS does not fix a maximum duration, but the express requirement of temporariness excludes reliance on Article 25(3) as a legal basis for permanent closure. The geographical requirement likewise demands identification of the waters in which the suspension operates.
The measure must be non-discriminatory in form and in fact among foreign ships. A suspension expressed in neutral language could still violate Article 25(3) if its practical application singled out ships of particular States. This condition operates independently of the requirement that the measure serve a legitimate security purpose.
Security is the substantive threshold. UNCLOS permits suspension only where it is “essential for the protection” of the coastal State’s security and identifies weapons exercises as an example (United Nations, 1982, art. 25(3)). The treaty's use of “essential” sets a demanding condition. Political convenience, commercial advantage, or a generalized preference to reduce foreign navigation does not satisfy the wording of the provision.
A suspension has no effect until it has been duly published. Publication is part of the legal mechanism by which Article 25(3) operates, not merely an administrative formality. Ships cannot be expected to comply with a territorial restriction that has not entered into effect in the manner required by the Convention.
7.2 Where Innocent Passage Cannot Be Suspended
The power in Article 25(3) does not apply to every maritime area in which UNCLOS uses the innocent-passage regime. Part III establishes special rules for straits used for international navigation, including circumstances in which innocent passage applies but suspension is expressly prohibited.
Article 45 identifies two such categories. The first concerns straits excluded from transit passage by Article 38(1), where a strait is formed by an island of the bordering State and its mainland and a route of similar convenience exists seaward of the island through the high seas or an exclusive economic zone. The second concerns straits between a part of the high seas or an exclusive economic zone and the territorial sea of a foreign State (United Nations, 1982, arts. 38 and 45).
In these straits, the innocent-passage regime of Part II applies subject to an important modification: Article 45(2) provides that there shall be no suspension. A coastal State cannot invoke Article 25(3) to interrupt innocent passage through waters falling within Article 45.
The applicable maritime classification is consequently decisive. Innocent passage may be temporarily suspended in an ordinary territorial-sea setting if Article 25(3) is satisfied. Where Article 45 governs an international strait, the same navigational right is non-suspendable.
8. Innocent Passage and Transit Passage
Innocent passage and transit passage perform related functions but operate under different legal regimes. Innocent passage governs navigation principally through the territorial sea under Part II of UNCLOS. Transit passage applies under Part III to qualifying straits used for international navigation between one part of the high seas or an exclusive economic zone and another such area, subject to the exceptions contained in the Convention (United Nations, 1982, arts. 17 and 37–38).
The difference is immediately apparent in the beneficiaries of each regime. Innocent passage is a right of ships and does not include a corresponding right of overflight through territorial airspace. Article 38, by contrast, grants transit passage to ships and aircraft and defines it through the freedom of navigation and overflight for continuous and expeditious transit of the strait.
Submarines illustrate the broader character of transit passage. Where innocent passage applies, Article 20 requires submarines and other underwater vehicles to navigate on the surface and show their flag. Part III contains no equivalent express requirement for transit passage. Article 39 instead requires ships and aircraft to refrain from activities other than those incident to their “normal modes” of continuous and expeditious transit. The widely accepted interpretation is that submarines may remain submerged when exercising transit passage because submerged navigation constitutes a normal mode of submarine operation (Tanaka, 2015).
Coastal regulatory authority is also structured differently. Article 21 permits legislation concerning innocent passage across subjects including navigational safety, maritime traffic, resources, environmental protection, research, and customs-related interests. Under the transit-passage regime, Article 42 permits States bordering straits to legislate in defined fields that include navigational safety, pollution, fishing by fishing vessels, and unlawful loading or unloading. Such laws may not discriminate among foreign ships or have the practical effect of denying, hampering, or impairing transit passage (United Nations, 1982, art. 42).
Suspension marks another major difference. Article 44 declares that there shall be no suspension of transit passage. Ordinary innocent passage, by contrast, may be temporarily suspended under Article 25(3) when its strict conditions are met. Article 45 creates an intermediate configuration: the applicable right remains innocent passage, but suspension is prohibited because the navigation occurs through specified international straits.
Neither regime changes the underlying legal status of the waters merely because foreign navigation is protected. Article 34 states that the passage regime through international straits does not otherwise affect the legal status of the waters forming the strait or the sovereignty or jurisdiction exercised by the bordering States. Transit passage grants broader navigational rights than ordinary innocent passage, but it remains a legal limitation on coastal authority rather than a conversion of territorial waters into high seas.
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Conclusion
Innocent passage protects navigation through waters that remain subject to coastal-State sovereignty. Article 17 recognizes the right, Article 18 determines what constitutes passage, and Article 19 identifies the central boundary between innocent and non-innocent conduct. The legal protection depends both on the navigational character of the voyage and on what the vessel does while within the territorial sea.
Coastal authority remains substantial, but UNCLOS does not leave it unlimited. Articles 21–23 permit regulation of defined interests and particular categories of shipping, while Articles 24 and 26 prevent regulation, discrimination, or financial charges from becoming mechanisms for extinguishing the right in practice. Article 25 adds protective powers against non-innocent passage and, in narrower circumstances, allows temporary suspension for essential security purposes.
Important questions are not fully settled. State practice continues to diverge over prior notification or authorization for foreign warships, and the relationship between the general standard in Article 19(1) and the activities listed in Article 19(2) remains open to competing interpretations. The consequence of submerged submarine navigation where the innocent-passage regime applies is also debated, as is the full range of measures available against an immune warship that refuses to comply with a lawful order to leave.
Maritime geography can alter the applicable rule. Ordinary innocent passage may be suspended under Article 25(3), whereas innocent passage through the international straits covered by Article 45 cannot be suspended. Transit passage affords broader protection in qualifying straits, extending to aircraft and, on the widely accepted interpretation of “normal modes,” submerged submarines, while Article 44 makes the regime non-suspendable. The law of innocent passage is thus neither unrestricted freedom of navigation nor complete coastal control: it is a treaty-based allocation of navigational rights and sovereign powers whose precise operation depends on the waters involved, the vessel’s conduct, and the legal regime applicable to the passage.
References
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United Nations Convention on the Law of the Sea (1982) adopted at Montego Bay, 10 December 1982, entered into force 16 November 1994, 1833 UNTS 3. Available at: https://treaties.un.org/Pages/showDetails.aspx?clang=_en&objid=0800000280043ad5 (Accessed: 10 September 2026).
United States of America and Union of Soviet Socialist Republics (1989) ‘Joint Statement by the United States of America and the Union of Soviet Socialist Republics, 23 September 1989 (Uniform Interpretation of Norms of International Law Governing Innocent Passage)’, Law of the Sea Bulletin, No. 14, pp. 12–13. Available at: https://www.un.org/depts/los/doalos_publications/LOSBulletins/bulletinpdf/bulE14.pdf (Accessed: 10 September 2026).
