San Remo Manual Rule 67

San Remo Manual Rule 67 is a provision of the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1994), the authoritative non-binding codification of customary naval warfare law developed by a group of legal experts under the International Institute of Humanitarian Law. Rule 67 addresses the circumstances under which neutral merchant vessels may lose their protected status and become lawful targets in naval armed conflict.

Under Rule 67, neutral vessels lose protection if they actively resist lawful interception or inspection, carry contraband, or are otherwise engaged in activities that make them legitimate military objectives. The rule is central to debates about visit and search rights, blockade enforcement, and proportionality in attacks on commercial shipping.

In the May 2026 tanker strikes context, Rule 67 was a primary reference for naval law scholars analysing whether the US F/A-18 strikes on M/T Sea Star III and M/T Sevda were lawful. The key arguments turned on whether Iranian-flagged tankers carrying sanctioned crude constituted a sufficient basis for their treatment as non-neutral vessels, and whether disabling rather than sinking satisfied the proportionality requirement.