What role do the San Remo Manual and naval warfare law play in restricting targeting of civilian ships at sea?

1. What the San Remo Manual is, in practice

The Manual was prepared by legal and naval experts under the International Institute of Humanitarian Law and published in the mid‑1990s as a “contemporary restatement” of the law applicable to armed conflicts at sea; states, courts and navies treat it as the principal modern reference for naval hostilities ^{[2] [1]}. It is not a treaty: it is an expert restatement that many commentators and some national manuals view as reflecting customary law, and its framers explicitly sought to harmonize naval practice with the Geneva Conventions and Additional Protocol I ^{[4] [5]}.

2. Core legal constraints on targeting civilian ships

The Manual contains detailed rules on “basic rules and target discrimination,” requiring parties to distinguish between combatant and civilian objects, to take precautions in attack, and to exempt certain vessels from attack (for example neutral merchant ships and medical transports) unless they are legitimate military objectives ^{[3] [6]}. It also sets out that blockades that have the sole purpose of starving civilians or denying objects essential for survival are prohibited ^[3]. Those provisions operate as limits on the right of belligerents to use any methods or means of warfare at sea ^[7].

3. How protections actually work: precautions, warnings and exemptions

San Remo requires parties to “take care to avoid damage” to civilian objects and to adopt precautions in attack — meaning attackers must verify targets, choose means and methods that minimize civilian harm, and, where feasible, issue warnings ^{[8] [7]}. The Manual divides categories (protected persons, medical transports, neutral merchant vessels) and prescribes when and how they may be intercepted, captured or attacked, thereby creating a practical legal framework that narrows permissible targeting ^{[6] [7]}.

4. Not a binding treaty — but influential and often cited

Because the Manual is an expert restatement rather than a formal multilateral treaty, its direct legal force depends on whether its rules reflect customary international law or are adopted by states. Scholars, the ICRC and naval establishments treat it as authoritative and it has been used in legal and political disputes — for example, it featured in legal arguments around the Gaza flotilla incident and in UN inquiry assessments ^{[3] [4]}. The IIHL and other bodies are actively working to update it to reflect modern challenges, signaling continued practical weight ^{[9] [10]}.

5. Areas of disagreement and limits of the Manual

Experts acknowledge errors and contested points in San Remo and note that some rules may not be fully grounded in contemporary state practice or opinio juris; the Manual’s treatment of new technologies (unmanned systems, cyber effects at sea) has prompted debate during revision discussions ^[8]. The ICRC and others argue the law needs updating because modern maritime interdependence and new weapons raise novel protection challenges ^[11].

6. How naval warfare law applies in contested, mixed-use seas

San Remo addresses operations in different maritime zones — internal waters, territorial seas, EEZs and the high seas — and explains how measures short of attack (interception, visit, search, capture) and blockades operate, while insisting on discrimination and humanitarian constraints even when exercising belligerent rights ^{[3] [6]}. In practice, belligerents retain broad operational discretion but must justify actions under the Manual’s rules; international scrutiny follows when civilian harm appears disproportionate or protections are ignored ^{[3] [4]}.

7. Practical takeaway for governments, navies and civilians

For states and navies, San Remo supplies the closest thing to a consolidated manual of naval targeting law and a yardstick for lawful behavior; for civilians and commercial shipping, it articulates protections and exemptions but depends on belligerent compliance and external enforcement mechanisms ^{[2] [7]}. Ongoing revision efforts and commentary from bodies such as the ICRC indicate the legal community expects the Manual’s norms to evolve in response to technological and strategic change ^{[9] [11]}.

Limitations: this analysis relies on expert restatements, institutional commentary and secondary reporting about how San Remo is used; available sources do not provide a comprehensive catalogue of every state practice or recent adjudications that definitively settle contested points ^{[2] [4]}.