Waging war at sea: Land warfare but just add water?

Abstract The experts who drafted the original San Remo Manual on International Law Applicable to Armed Conflicts at Sea (San Remo Manual) sought to enhance humanitarian protections for civilian navigation, including by incorporating elements of the 1977 Additional Protocol I (AP I) rules on the conduct of hostilities. This approach was notwithstanding Article 49(3)–(4) of AP I, which limits the application of these treaty rules to sea warfare affecting civilians and civilian objects on land, and preserves existing treaty and customary law protections at sea. The rationale for extending these AP I rules to naval warfare without landward effects is not always clearly articulated in the San Remo Manual. If intended as a response to the excesses of the Second World War – particularly the expansion of attacks against merchant vessels – this move is understandable. However, to the extent that key aspects of the traditional law of naval warfare endured after the war, then arguably this move represented an expansion of belligerent rights and a corresponding narrowing of humanitarian obligations. The application of AP I’s land warfare “targeting” rules to sea was already the subject of significant academic debate in the 1980s, making the San Remo Manual’s position a decisive development. Since 1994, many States have adopted a similar approach in their military manuals, often citing the San Remo Manual as a reference. This article examines the significance of that decision taken by the San Remo Manual’s drafters and argues that the fit between the traditional law of naval warfare and the AP I targeting framework remains an uneasy one at times – especially as regards merchant vessels, their cargo, and civilian crews and passengers. Although the San Remo Manual itself acknowledged this tension, it has not been fully explored in subsequent scholarship. This article argues that in relation to the traditional law of naval warfare “belligerent rights” of visit and search and blockade, aspects of the traditional law should be “restored” concerning the use of force against merchant vessels. This approach better reflects the San Remo Manual’s underlying humanitarian objectives while addressing persistent ambiguities in the application of distinction, proportionality and precautions at sea – areas that are in urgent need of clarification as part of the ongoing update of the San Remo Manual and in State practice.