Property, Not Immunity: UNCLOS and Maritime Autonomous Vessels

Can Maritime Autonomous Vessels (MAVs) claim sovereign immunity under UNCLOS? This article answers firmly: they cannot. MAVs are property, not immune vessels — a restrictive reading that preserves doctrinal integrity and coastal state rights.

The rise of MAVs in naval and maritime operations has made this question unavoidable. If they were treated as warships or government vessels, they could operate in foreign waters shielded from coastal state authority, unsettling the balance and predictability of the maritime legal order.

The analysis proceeds in two stages. First, it applies UNCLOS’s doctrinal thresholds to demonstrate why MAVs fail the definition of “ship” and “warship.” Second, it examines the regulatory and strategic implications of this restrictive reading, showing how treating MAVs as property preserves accountability, safeguards sovereignty, and maintains stability in the evolving maritime domain. The conclusion integrates both doctrinal and policy dimensions, underscoring why immunity must remain confined to vessels that embody command and crew.

For the broader doctrinal foundation, see related article: MAVs and Coastal State Security: A Restrictive Reading of UNCLOS.

Core Rule

Under UNCLOS, “warship” means a ship belonging to the armed forces of a State bearing the external marks distinguishing such ships of its nationality, under the command of an officer duly commissioned by the government of the State and whose name appears in the appropriate service list or its equivalent, and manned by a crew which is under regular armed forces discipline.¹

UNCLOS also extends immunity to “other government ships operated for non‑commercial purposes.” This category includes coast guard ships, fisheries enforcement vessels, customs patrol craft, and other maritime law enforcement platforms.²

MAVs do not independently qualify as warships nor as government ships operated for non‑commercial purposes. Any immunity they possess is confined to the mothership. MAVs must therefore be treated as property, not vessels with sovereign immunity.

Definition and Scope

MAVs are watercraft capable of operating with varying degrees of autonomy, ranging from automated decision support to full independence from human control.³ MAVs are generally utilized for tasks such as intelligence, surveillance, reconnaissance, mine countermeasures, logistics, rescue, and force protection.

For this article, MAVs refer only to those with third- and fourth-degree autonomy, which operate without crew, and fall outside the UNCLOS’ intended scope for ships. They are better classified as auxiliary equipment or systems.

See related article: MAVs and Coastal State Security: A Restrictive Reading of UNCLOS.

Doctrine: Elements and Tests

The status of MAVs under UNCLOS must be tested against distinct doctrinal thresholds. Each category carries separate legal consequences, and MAVs fail at every stage, as follows:

1. Ship – UNCLOS employs the term ships in its ordinary sense: traditional, manned, navigable vessels capable of fulfilling duties at sea. This baseline interpretation already excludes MAVs, which are unmanned systems, whether remotely operated or fully autonomous. They do not meet the threshold concept of “ship” under the Convention.

2. Warship – applying the elements under Article 29 ⁴ demonstrates why MAVs cannot qualify as warships:

• Belonging to the armed forces of a State – MAVs may be employed by naval forces, but operational use alone does not override UNCLOS’ substantive requirements. Listing or assigning them to units cannot substitute for the legal definition of warship.
• Bearing external marks of nationality – MAVs may display identifiers, but nationality marks are evidentiary only. They cannot substitute for the absence of a command and crew.
• Commanded by a commissioned officer – MAVs are remotely operated or pre‑programmed, with no officer physically in command onboard. Remote oversight does not satisfy Article 29’s requirement of onboard command.
• Manned by a crew under regular armed forces discipline – MAVs are unmanned and lack a physically embarked crew subject to the discipline of the regular armed forces. Under UNCLOS, discipline attaches to personnel onboard, accountable under military law and command authority. Remote operators, even if subject to discipline ashore, do not meet this requirement because the Convention intended discipline to be exercised by an embarked crew.

Taken together, MAVs fail every cumulative requirement of Article 29. They cannot be stretched into the definition of a warship.

3. Other Government Ships – Article 32 preserves sovereign immunity for government ships operated for non‑commercial purposes.⁵ These vessels may bear nationality marks and operate under state authority, but MAVs cannot be reclassified into this category. They lack the defining attributes of ships and remain auxiliary equipment. While some states designate MAVs as property of the armed forces or register them under government ownership, such practice does not alter their legal status. Immunity attaches only to vessels that embody UNCLOS’s intention at the time of its adoption — ships with command, crew, and accountability.

4. Deployed from Sovereign Immune Motherships – A further doctrinal nuance arises when MAVs are deployed from government ships or warships that enjoy immunity. The immunity of the mothership does not extend to detachable systems. Sovereign immunity cannot be transmitted through derivative tethering. MAVs remain property, supplementary systems or equipment, even when deployed from sovereign immune platforms.

Regulatory and Doctrinal Treatment of MAVs

The classification of MAVs carries significant implications for their use, particularly regarding protection from seizure and the extension of sovereign immunity. In the absence of clear international regulation, prevailing practice has been to register these platforms in ways that emphasize state ownership and operation, thereby linking them to sovereign accountability. This practical approach ensures responsibility remains with the state, but it is provisional and highlights the urgent need for a coherent legal framework.

Commentaries increasingly debate whether UNCLOS encompasses MAVs. Some argue that the Convention presupposes crewed vessels and therefore excludes MAVs from its definitional framework, while others explore whether evolving practice might justify their inclusion.⁶ What remains clear is that UNCLOS’s intention at the time of adoption was directed toward traditional ships with command and crew.

Moreover, the IMO’s Regulatory Scoping Exercise for MASS has identified gaps in the existing framework, and the awaited IMO Code is expected to clarify the legal status of autonomous systems and their relationship to sovereign immunity.⁷ Until a new regulation is adopted, MAVs remain outside UNCLOS’s intended scope of ships and are unable to invoke sovereign immunity with certainty.

Conclusion

MAVs cannot be classified as warships under UNCLOS, nor do they qualify as operated for non-commercial purposes. Lacking command and crew, they remain auxiliary equipment rather than vessels in their own right. Sovereign immunity attaches only to ships that meet UNCLOS’s strict definitions; it does not extend to unmanned systems, however advanced.

This restrictive interpretation is both a safeguard and a principle. It prevents immunity from expanding to technologies never contemplated by UNCLOS, preserves coastal state jurisdiction, and ensures accountability. Without crews, MAVs cannot identify themselves, respond to hails, or fulfill duties such as rescue or reporting, heightening the risk of miscalculation, cyber intrusion, and escalation.

By treating MAVs as property, states can embrace technological progress while safeguarding sovereignty, stability, and the integrity of the maritime legal order. Immunity is a privilege reserved for vessels that embody command and accountability. Holding firm to this principle ensures that the balance between the flag state’s rights and the coastal state’s sovereignty remains intact in the evolving maritime domain.

1. United Nations Convention on the Law of the Sea, Dec. 10, 1982, 1833 U.N.T.S. 397, art. 29 [hereinafter UNCLOS]. ↩︎
2. Id, art. 32. ↩︎
3. Int’l Maritime Org., Outcome of the Regulatory Scoping Exercise for the Use of Maritime Autonomous Surface Ships (MASS), IMO Doc. MSC.1/Circ.1638 (June 3, 2021) [hereinafter IMO, Outcome of RSE for MASS]. ↩︎
4. UNCLOS, art. 29. ↩︎
5. Id, art. 32. ↩︎
6. House of Lords, UNCLOS: The Law of the Sea in the 21st Century, Int’l Relations & Defence Comm. Rep., HL Paper 159 (2023); James Kraska, Warships and Sovereign Immunity, 40 Int’l J. Marine & Coastal L. 719 (2025); Natalie Klein, Maritime Autonomous Surface Ships and International Law, 36 Ocean Y.B. 45 (2022); Wolff Heintschel von Heinegg, The Law of Naval Warfare and Unmanned Systems, 98 Int’l Rev. Red Cross 567 (2016). ↩︎
7. IMO, Outcome of RSE for MASS. ↩︎