Maritime Operations and IHL


Naval forces have often been incredibly important in determining the fate of a conflict and this has only intensified with the growth of maritime trade and technology. Countries practiced seaward sieges and naval bombardment as early as the Peloponnesian wars in the fifth century BC.1Phillip J. Drew, ‘Can We Starve the Civilians? Exploring the Dichotomy between the Traditional Law of Maritime Blockade and Humanitarian Initiatives’ (2019) 95 Int’l L Stud Ser US Naval War Col 302 Currently, naval warfare is at the forefront of the advent of autonomous marine vehicles which can be used in an armed conflict. The laws of war, however, is a lex specialis area of naval warfare which have not yet been adequately codified and while soft law instruments fill this gap somewhat, it remains an underwritten area of the law.

This month at the Diplomacy Law and Policy forum, we are looking at marine operations under IHL, focusing on the history of naval warfare, maintaining maritime peace, and piracy. This editorial meanwhile offers a primer on how the laws of war apply (and to some degree how they do not) in contrast to war ashore, issues relating to war at sea, namely blockades, maritime exclusion zones, and autonomous vehicles.

Maritime Operations and IHL

The law of naval warfare has not been as codified as the laws of war generally.2Jonathan G. Odom, ‘Guerrillas in the Sea Mist: China’s Maritime Militia and International Law’ (2018) 3 Asia Pac J Ocean L & Pol’y 31 Klein et al argue that the “law of naval warfare is notorious for its laggard treaty-law basis and, consequently, its heavy reliance on custom, application by analogy, and soft law (predominantly in the form of Manuals)”.3Klein However, what little has been crystallised is found in the Second Geneva Convention which focuses on naval warfare and the Hague Conventions of 19074Hague Convention (viu) Relating to the Conversion of Merchant Ships into Warships, Oct. 18, 1907; Hague Convention (viii) Relative to the Laying of Automatic Submarine Contact Mines, Oct. 18, 1907; Hague Convention (ix) Concerning Bombardment by Naval Forces in Times of War, Oct. 18, 1907; Hague Convention (xi) Relative to Certain Restrictions with Regard to the Exercise of the Right of Capture in Naval War, Oct. 18,1907; Hague Convention (xiii) Concerning the Rights and Duties of Neutral Powers in Naval War Oct. 18, 1907 also govern means and methods of warfare at sea. Meanwhile, the San Remo Manual of 19955San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1994) is a soft law instrument which applies the laws of war as well as the UN Convention on the Laws of the Sea (UNCLOS) to nautical conflict.

The cardinal principles of the laws of war continue to apply to naval warfare, however, they apply a bit differently to how they do ashore. Indeed, the obligation to distinguish between civilians and combatants at sea, to conduct a proportionality assessment, to exercise precautions in attack, and to avoid making civilians the object of an attack has been specifically excluded from naval warfare. Article 49 of Additional Protocol I which states that the provisions of Articles 48 to 67 “apply to any land, air or sea warfare which may affect the civilian population, individual civilians or civilian objects on land. They further apply to all attacks from the sea or from the air against objectives on land but do not otherwise affect the rules of international law applicable in armed conflict at sea or in the air”. This acknowledges that the law of naval warfare is lex specialis and remains applicable regardless of the application of these principles to war ashore.6Lee However, these cardinal principles are not codified in their application to war at sea though that does not mean that they do not apply in some form at all.

While the laws of law as they apply on land focus on an individual-based status, the laws of naval warfare establish a vessel-based status.7Lee For a marine vessel, the status of a warship is significant as they are the only ones who possess belligerent rights to engage in hostilities. Article 29 of UNCLOS defines a warship as “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”.  The law of naval warfare therefore envisages war to be the prerogative of official state warships against enemy warships.

The other types of marine vehicle relevant to an armed conflict are auxiliary vessel which as per the San Remo Manual is a “vessel, other than a warship, that is owned by or under the exclusive control of the armed forces of a State and used for the time being on government non-commercial service”. An auxiliary vessel does not possess a command or a crew like a warship, but remains under the exclusive control of the military and can be used to resupply warships or to carry troops and war materiel.8Klein They can be called ‘lily pads’ for the delivery of troops, intelligence collectors, or reconnaissance platforms.9David T. Lee, ‘The Principle of Proportionality in Maritime Armed Conflict: A Comparative Analysis of the Law of Naval Warfare and Modern International Humanitarian Law’ (2021) 27 Sw J Int’l L 119 As a result, they remain a military objective and can be targeted in an armed conflict, this is despite the fact that it seems they cannot engage in hostilities in the same way a warship can, in that, for instance, they cannot attack submarines as that remains a prerogative for warships.10Klein

Furthermore, the notion of direct participation of hostilities also applies to vessels, therefore, fishing vessels, hospital ships, and merchant ships are exempt from capture unless they take a part in hostilities.11Hague Convention (xi) Relative to Certain Restrictions with Regard to the Exercise of the Right of Capture in Naval War, Oct. 18, 1907, art. 3 As per the San Remo Manual, enemy merchant vessels can be attacked if they are military objectives. It further gives examples of activities which may render a vessel to be a military target, such as laying mines, attacking enemy vessels, minesweeping, and cutting undersea cables. Moreover, undertaking a reconnaissance mission or refusing an order or resisting visit, search or capture, and being armed, would render a vessel an auxiliary vessel.

As warships are military objectives due to their vessel-based status it is presumed that civilians would be excluded from these vessels.12Lee This is in part because it would be impractical to individually distinguish those aboard each vessel as being a civilian or combatant and due to the notion that all hands act as one on deck and therefore will be targeted as one.13Lee As a result, the principle of proportionality does not quite apply in the same way, as, so long as the status of a ship is a military objective, the presence of civilian crew on board can largely be ignored.14Lee In terms of the status of individuals involved in naval warfare, civilian crews of merchant vessels and auxiliaries are to be accorded prisoner of war status upon capture and they enjoy combatant privilege for acts undertaken during hostilities. This seems to endeavour to extend protection to civilian crews, a protection which is stripped in vessel-based targeting allowances under the law of naval warfare.


A key issue in IHL which relates to maritime warfare is the use of blockades under which a belligerent may exclude all transit into and out of a defined area or location.15Drew While Article 54 of Additional Protocol I prohibits the starvation of civilians as a method of warfare, it can be argued that starvation is a side effect of a blockade and not its main purpose. However, it has been contended that allowing naval blockades which lead to the starvation of a civilian population is untenable with the object and purpose of IHL. As a result, the San Remo Manual addresses this lack of clarity in Articles 102 and 103. These provisions state that a blockade is prohibited if it solely aims to starve the civilian population or deny it objects essential for its survival, or if the damage to the civilian population is expected to be excessive in relation to the concrete and direct military advantage anticipated from the blockade. It also provides for states to grant humanitarian access if the civilian population is inadequately provided with food or other objects essential for its survival. Therefore, the drafters of the Manual incorporated a proportionality requirement in order to ensure civilian protection during a blockade.16Drew However, the Manual remains a soft law instrument and as such, without state practice or opinio juris it has not crystallised into customary international law. Drew argues that “In the current political environment, it is unlikely that States could reach a broad international agreement on a renewed law of blockade…Until that occurs, the law with respect to humanitarian initiatives will remain unsettled and States may engage in the deliberate starvation of civilians with little or no concern that they will be held accountable for their actions”.17Drew

Maritime Exclusion Zones

Maritime exclusion zones have been used by belligerents since the start of the twentieth century to control or prohibit the access of foreign ships.18Raul Pedrozo, ‘Maritime Exclusion Zones in Armed Conflicts’ (2022) 99 Int’l L Stud Ser US Naval War Col 526 They are often used to warn vessels to avoid an area in which hostilities were being conducted, to reduce the chance of them being wrongly targeted as a military objective.19Pedrozo However, a vessel’s entry into this zone does not render it a lawful target simply by being there and it must still be distinguished as a warship or auxiliary vessel before being targeted lawfully. Moreover, the extent, location, and duration of a MEZ and measures used to enforce it are to not go beyond that required by military necessity.20Pedrozo Though an MEZ does not affect a belligerents’ right to control the area of hostilities in which a commander may restrict the activities of neutral vessels and aircraft to ensure battlespace management.21Pedrozo It may be that the disadvantage to the use of such exclusion zones are the same as they are ashore, in that they also signify where non-military objectives are kept, rendering them perhaps more vulnerable to targeting.

Maritime Autonomous Vehicles

Maritime autonomous vehicles (MAVs) are being used more and more in the oceans, for instance in oil spill removal, cargo shipments, surveying fish abundances, and even in anti-terrorist measures to intercept boats carrying explosives.22Natalie Klein , Douglas Guilfoyle, Md Saiful Karim & Rob McLaughlin, ‘Maritime Autonomous Vehicles: New Frontiers in the Law of the Sea’ (2020) 69 Int’l & Comp LQ 719 A key issue arising with states’ use of MAVs for military purposes is whether they possess immunity or not.23Klein Under the UNCLOS regime, warships and government ships operated for non-commercial purposes have immunity which prevents them from being seized by other states. This may apply to MAVs so long as they satisfy the criteria of being a ‘ship’, in that as per Article 30 of UNCLOS they must be under the command of a military officer and crewed by those under regular armed forces discipline.24Klein It is unclear whether this would apply to remotely powered MAVs which are commanded by those ashore. Klein et al argue that the original drafters wished to outlaw privateering in their definition of a warship and therefore MAVs could qualify as warships.25Klein The status of those operating MAVs from the shore though is not yet clear – while if they were on board the ship they would be granted combatant immunity and prisoner of war status upon capture, it is not clear if that carries by analogy if they are not present at sea.26Klein Instead, they may be civilians who directly participate in hostilities and remain prosecutable under domestic law for actions conducted during an armed conflict even if they are lawful acts of war.27Klein


The law of naval warfare is a subset of the laws of war and yet remain rather far behind in terms of their codification and the clarity (perhaps also the degree of debate) regarding their application. The cardinal principles may not carry over by analogy to war at sea given its special and particular circumstances, and indeed it would be highly impractical and not feasible to require that every individual member of a crew be identified prior to targeting or even for a proportionality analysis. However, it does seem that extending prisoner of war status to civilian crews in the event of capture attempts to forestall the loss of protection in determining status on the basis of vessels rather than individuals. The increasing use of autonomous vehicles may lead to a need to codify further the laws of naval warfare whether through more soft law or treaty instruments. Any such endeavor would be welcomed.


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