Maritime Autonomous Vessels and Coastal State Security: A Restrictive Reading of UNCLOS

Maritime Autonomous Vessels (MAVs) are reshaping the maritime domain. On one hand, they present risks: highly autonomous systems, such as Unmanned Surface Vessels, can approach critical infrastructure without clear legal guidance on interception, raising the danger of miscalculation or escalation. On the other hand, they offer stability: a coherent doctrine rooted in the United Nations Convention on the Law of the Sea (UNCLOS) provides predictability, enabling coastal states and operators to balance innovation with sovereignty. Clarifying MAVs’ legal status is therefore essential to safeguard maritime order while accommodating technological progress.

Core Rule

UNCLOS uses the term “ship” to refer to traditionally manned, navigable vessels. Its provisions, such as flag state duties, penal jurisdiction, and the duty to render assistance, presume human presence on board.¹ MAVs with first- and second-degree autonomy, where crew remain capable of control, may be treated as ships and enjoy the rights of passage. By contrast, MAVs with third- and fourth-degree autonomy, which operate without crew, fall outside the treaty’s intended scope. They are better classified as specialized equipment or systems, not ships, and thus do not automatically enjoy the rights accorded to traditional vessels.

Definition & Scope

MAVs are watercraft capable of operating with varying degrees of autonomy, ranging from automated decision support to full independence from human control. The International Maritime Organization (IMO), through its regulatory scoping exercises, has categorized Maritime Autonomous Surface Ships (MASS) into four degrees of autonomy:

• First Degree – Ships with automated processes and decision support, but with crew on board ready to assume control.
• Second Degree – Remotely controlled ships with crew on board capable of taking over operations.
• Third Degree – Remotely controlled ships without crew on board.
• Fourth Degree – Fully autonomous ships whose operating systems make decisions independently.²

These distinctions highlight the challenges of applying crew‑based conventions to unmanned vessels.³ MAVs are not traditional ships under UNCLOS when they lack a crew capable of navigation and operational control. This categorical separation underscores the difficulty of extending existing maritime obligations, such as reporting, liability, and navigational duties, to vessels that operate without human presence.

Doctrine: Elements and Tests

Crew Presence and Doctrinal Classification

The presence of crew aboard a vessel remains the defining characteristic for its recognition as a “ship” under international law. A crew member physically on board ensures that the vessel can be controlled, navigated, and held accountable for compliance with international obligations. This requirement also provides a clear line of responsibility in cases of collision, distress, or environmental harm. Without crew presence, MAVs cannot meet the expectations of accountability and responsiveness that UNCLOS presumes, leaving them outside the category of ships.⁴ This principle creates a doctrinal classification: first‑ and second‑degree MAVs, with crew aboard, may be treated as ships and enjoy the rights of passage, while third‑ and fourth‑degree MAVs, operating without crew, are better understood as specialized systems subject to coastal state jurisdiction. This categorical separation ensures predictability in maritime governance and protects the sovereignty of coastal states. It also prevents unmanned vessels from invoking rights they cannot fulfill, such as innocent passage or transit passage, thereby maintaining the integrity of UNCLOS’s framework.

Flag State Duties

Flag states carry the primary responsibility for ensuring that vessels flying their flag comply with international standards of safety, navigation, and competence. In the case of MAVs, this responsibility becomes more complex when no crew is physically present to meet those standards. The absence of human operators raises questions of accountability, particularly in areas such as certification, training, and compliance with international safety regimes. Without a crew aboard, it is unclear how flag states can demonstrate compliance with obligations that presuppose human oversight. The IMO’s scoping exercises confirm that existing conventions continue to assume human operators, underscoring the regulatory gap that MAVs create.⁵

Navigation Responsibility

Traditional maritime law assigns duties such as rescue, reporting, and liability in collisions to the master and crew of a vessel. These obligations depend on human judgment and immediate response. Third- and fourth-degree MAVs cannot fulfill these responsibilities in practice, leaving a doctrinal gap where accountability is expected but absent.

The gap analysis of the FAL Convention illustrates this problem: its reporting and facilitation requirements assume human crews to prepare and submit documentation, yet autonomous vessels lack the personnel to comply. This reinforces the need for new frameworks that can accommodate non‑human operators. Until such frameworks are developed, MAVs without crew remain unable to meet the responsibilities expected of ships under international law.⁶

National Security Protection

National security considerations reinforce the restrictive interpretation of MAV rights. Unmanned vessels approaching territorial seas or archipelagic waters without clear identification pose risks of miscalculation, cyber intrusion, or diversionary tactics. For example, incidents in the Persian Gulf have shown how remotely operated or drone‑like vessels can be used to shadow or harass commercial shipping, raising tensions and forcing coastal states to adopt defensive postures. Similarly, reports of GPS spoofing and cyber interference in the Black Sea highlight vulnerabilities when vessels lack human crews to respond in real time.

These risks also intersect with the doctrine of sovereign immunity. Under UNCLOS, immunity attaches only to vessels that meet the strict definition of warship.⁷ MAVs, even when deployed from a manned naval platform, do not independently satisfy the criteria for a warship. They should therefore be treated as property or auxiliary systems of the sovereign immune vessel, not as warships in their own right. This restrictive position preserves doctrinal integrity and protects coastal state rights, preventing unmanned systems from penetrating territorial seas or archipelagic waters without accountability.

In the absence of binding international regulations, coastal states are justified in denying entry or imposing strict controls on such equipment or systems.

See also: Sovereign Immunity at Sea Under UNCLOS: Meaning, Boundaries, and Operational Use

Relevant Jurisprudence

North Atlantic Coast Fisheries (Great Britain/United States), PCA Award (1909) – This arbitration arose from disputes over fishing rights off Newfoundland under the 1818 Treaty. The tribunal emphasized contemporaneous interpretation, holding that treaty terms must be understood as they were at the time of drafting. In practice, this meant limiting “ships” to manned vessels engaged in traditional fishing. For MAVs, the ruling illustrates how tribunals privilege original intent, supporting a restrictive reading of UNCLOS that excludes unmanned vessels from navigational rights.⁸

Rights of Nationals of the United States of America in Morocco (France v. United States), ICJ Judgment (1952) – This case concerned consular jurisdiction and treaty rights in Morocco. The International Court of Justice stressed that treaty provisions must be interpreted in light of their historical context and the intentions of the parties. The Court’s reasoning reinforces the position that UNCLOS provisions presuppose human crews, since the drafters in 1982 could not have contemplated fully autonomous vessels. For MAVs, this jurisprudence strengthens the doctrinal view that third- and fourth-degree vessels should not automatically be treated as ships.⁹

Liability and Accountability

Liability in the context of MAVs remains unsettled. Existing maritime frameworks presuppose the presence of a master and crew, making it difficult to apply obligations such as penal jurisdiction, collision responsibility, and the duty to render assistance to autonomous systems.¹⁰ When MAVs operate without crew, these obligations cannot be meaningfully discharged, creating a doctrinal gap.

In practice, accountability may shift to flag states, operators, or manufacturers. Analogies from aviation drones and autonomous vehicles suggest that product liability and operator negligence frameworks may supplement maritime law, though these analogies remain imperfect.¹¹ More critically, liability implicates state responsibility: when an unmanned MAV causes damage in another state’s waters, attribution becomes complex. Without a crew aboard, it is unclear how responsibility attaches, yet international law requires that states remain answerable for the conduct of their vessels. Maritime-specific doctrines such as limitation of liability, safety conventions, and collision regulations further illustrate the challenge, since they presuppose human operators and traditional shipowner‑crew relationships.¹² Until instruments like the IMO’s MASS Code provide clarity, liability for MAVs will remain fragmented, reinforcing the necessity of treating them as specialized equipment subject to coastal state jurisdiction

Conclusion

The future of MAVs under UNCLOS must be guided by a restrictive and doctrinally anchored approach. UNCLOS was drafted with manned vessels in mind, and its obligations cannot be meaningfully applied to fully autonomous systems. First‑ and second‑degree MAVs may be classified within the category of ships, but third‑ and fourth‑degree MAVs are better understood as specialized equipment subject to coastal state jurisdiction.

This position is not simply provisional; it is required to preserve the integrity of UNCLOS. Extending sovereign immunity or navigational rights to unmanned systems would weaken coastal state sovereignty and unsettle maritime order, while giving advanced navies advantages that UNCLOS was never meant to provide. By treating MAVs as property of the mothership, international law maintains accountability, protects jurisdictional authority, and ensures predictability in maritime governance.

As the framework for MAVs develops, states should continue to anchor their practice in UNCLOS’s restrictive framework. Only through doctrinal clarity and respect for coastal state rights can international law adapt to technological progress without compromising sovereignty and security.

Footnotes

1. United Nations Convention on the Law of the Sea, Dec. 10, 1982, 1833 U.N.T.S. 3 (entered into force Nov. 16, 1994) [hereinafter UNCLOS]. ↩︎
2. IMO, Outcome of the Regulatory Scoping Exercise for the Use of MASS, IMO Doc. MSC.1/Circ.1638 (June 3, 2021). ↩︎
3. IMO, Outcome of the Regulatory Scoping Exercise and Gap Analysis of the FAL Convention with respect to MASS, IMO Doc. FAL.5/Circ.49 (June 1, 2022). ↩︎
4. UNCLOS, supra note 1, art. 94; IMO, Outcome of the Regulatory Scoping Exercise for the Use of MASS, supra note 3. ↩︎
5. Id. ↩︎
6. UNCLOS, supra note 1, arts. 97–98; IMO, Outcome of the Regulatory Scoping Exercise and Gap Analysis of the FAL Convention with respect to MASS, supra note 4. ↩︎
7. UNCLOS, supra note 2, art. 29. ↩︎
8. North Atlantic Coast Fisheries (Gr. Brit./U.S.), Award, Perm. Ct. Arb., Sept. 7, 1909, 11 U.N. Rep. Int’l Arb. Awards 167. ↩︎
9. Rights of Nationals of the United States of America in Morocco (Fr. v. U.S.), Judgment, I.C.J. Rep. 176 (1952). ↩︎
10. UNCLOS, supra note 1, arts. 97–98. ↩︎
11. King’s College London, Autonomous Vehicles: Automotive, Maritime and Aerial (2022). ↩︎
12. Convention on Limitation of Liability for Maritime Claims (LLMC); International Convention for the Safety of Life at Sea (SOLAS); & Convention on the International Regulations for Preventing Collisions at Sea (COLREGs). ↩︎