Innocent passage and marine environmental protection of remotely operated MASS: functional equivalence and coastal state jurisdiction

Although the timing and scale of commercial deployment remain uncertain, remotely operated and autonomous ship technologies have moved beyond the hypothetical stage, as reflected in the adoption of the 2026 non-mandatory MASS Code and the planned IMO experience-building process. This article examines remotely operated Maritime Autonomous Surface Ships (MASS) with no persons on board, focusing on how environmental protection functions traditionally performed by the master and seafarers are redistributed among shipboard systems, a Remote Operations Centre (ROC), remote operators, and external support arrangements. It addresses two questions: whether the pollution-prevention, reporting, emergency-response, and cooperation functions required under the existing international framework can be maintained at an equivalent level under this operational structure, and to what extent coastal States may exercise pre-incident regulation and post-incident enforcement in the territorial sea without impairing innocent passage or altering the allocation of jurisdiction under UNCLOS. Using a doctrinal and interpretive analysis of UNCLOS, relevant IMO instruments, the MASS Code, and international case law, the article distinguishes measures available under existing law from areas requiring further normative development. It argues that functional equivalence should not be treated as an independent basis of coastal State jurisdiction, but as an analytical criterion for assessing whether the existing level of marine environmental protection is effectively maintained. At the pre-incident stage, common international criteria should assess effectiveness, timeliness, continuity and reliability, fallback capability, and external verifiability across the pollution-response chain, while coastal State measures must remain within existing jurisdictional limits and satisfy requirements of necessity, proportionality, non-discrimination, and consistency with innocent passage. At the post-incident stage, orders to stop and measures used to compel a vessel to stop, remote verification and physical inspection, detention, and the preservation and acquisition of digital evidence should be treated as legally distinct measures, each subject to its own legal basis, triggering conditions, and procedural safeguards. The article concludes that the principal regulatory task is not to create new coastal State powers for MASS, but to clarify how existing environmental protection and enforcement functions can operate effectively when relevant human and informational functions are performed remotely.