Merchant Shipping as Military Objectives and Naval Economic Warfare


| Aug 7, 2023

Economic Warfare

On July 17, 2023, within 48 hours of the suspension of the Black Sea Grain Initiative, Russia and Ukraine made pivotal declarations potentially expanding the scope of their hostilities to a hitherto unprecedented scale. Both States declared their willingness to potentially treat all vessels sailing to their adversary’s ports as military objectives, rendering such vessels liable for diversion, capture, or destruction. These declarations have resurrected a long dormant debate on the practice of economic warfare embedded in the law of naval warfare and the relationship of the law of naval warfare to the fundamental principles of general international law. Apropos the first debate, this post notes that the reigning consensus in international humanitarian law is heavily weighted against the validity of the practice of economic warfare. Apropos the second debate, a harmonious interpretation necessitates a reconsideration of the balance between belligerent and neutral rights, which lies at the heart of the law of naval warfare.

Open Season in the Black Sea?

As the ongoing Russian war of aggression in Ukraine progresses well into its second year, the world’s eyes remain transfixed on the ongoing Ukrainian counter-offensive on land. However, an incredibly significant development has also occurred at sea. Over the course of 24 hours and in less than 500 characters, both Russia and Ukraine have declared their intention to potentially consider any vessel sailing toward their adversary’s port in the Black Sea as a potential carrier of military cargo.

On 19 July, the Russian Defense Ministry released the following statement:

from 00.00 Moscow time on 20 July 2023, all vessels sailing in the waters of the Black Sea to Ukrainian ports will be regarded as potential carriers of military cargo. Accordingly, the countries of such vessels will be considered to be involved in the Ukrainian conflict on the side of the Kiev regime. In addition, a number of sea areas in the north-western and south-eastern parts of the international waters of the Black Sea have been declared temporarily dangerous for navigation … .

The following day, Ukrainian Ministry of Defense released its own statement:

from the 21st of July 2023 00:00 Kyiv Time, all vessels in the Black sea waters that head to the ports of the russian federation or to temporarily occupied ports of Ukraine, may be considered for risk assessment as vessels carrying a military cargo. Moreover, navigation in the North-East Black Sea region and the Kerch-Yenikal strait has been declared dangerous and prohibited … .

Merchant Shipping as Military Objectives

The implication of a ship being characterized as a carrier of military cargo is that it can be classified as a military objective and thus be rendered a legitimate object for military targeting. Indeed, this is exactly what the United States, the United Kingdom and Ukraine have suggested is intended by Russia. Coincidentally, it is Ukraine that has now acted thus by having targeted a Russian fuel tanker and declaring that six Russian Black Sea ports are now “war risk areas.”

Article 52(2) of Additional Protocol I (AP I) to the Geneva Conventions defines military objectives as “those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage.” This provision is also regarded as reflective of customary international law.

AP I requires objects to make an effective contribution to military action before being transformed into military objectives. However, at sea, ships can be transformed into a military objective even if they are not engaging in belligerent acts nor making an effective contribution to military action. As the lex specialis, the law of naval warfare provides a detailed regime governing hostilities occurring at sea and allows for a more expansive understanding of a military objective.

A ship can so easily be transformed into a military objective because, unlike the laws of land warfare, at sea the targeting of merchant shipping has long been accepted as part of the practice of economic warfare. Per this practice, (absent special protections) an enemy’s merchant ships and its cargos are lawful prize and are always subject to capture. On the other hand, neutral shipping cannot be interfered with unless it engages in unneutral service, carries contraband, or engages in any other activity that renders it a military objective.

Rule 40 of the San Remo Manual (widely considered to represent an authoritative restatement of the international law applicable to armed conflicts at sea) also reproduces the definition of military objectives found in Article 52(2) of AP I. However, Rules 60 and 67 of the San Remo Manual provide domain-specific details about the circumstances in which enemy and neutral merchant vessels can become military objectives. Both enemy merchant and neutral merchant vessels do qualify as military objectives if they make an effective contribution to military action. However, because an enemy merchant vessel is always subject to capture, it also becomes a military objective if it refuses an order to stop or actively resists visit, search, or capture. By contrast, a neutral merchant vessel can be attacked only if reasonable grounds exist to assume that it is carrying contraband or is breaching a blockade and it refuses to stop or clearly resists visit, search, and capture.

Economic Warfare and the Law of Naval Warfare

What then explains the divergence in between the approach endorsed by the AP I and the approach endorsed by the law of naval warfare in defining a military objective? Under AP I, transformation of an object into a military objective occurs only in cases where it makes an effective contribution to military action. By contrast, the law of naval warfare goes well beyond this. The reason lies in the historical acceptability of the doctrine of economic warfare at sea. The forcible methods of economic warfare include the regimes of blockade, contraband, visit and search, and prize law. My concern here is not to consider whether the requirements of the law of blockade or the law of contraband have been satisfied (even as existing analyses suggests that they have not). Rather, it is to consider their very basis itself.

Some regimes like the law of contraband and the right of search and visit can indeed accomplish narrow and legitimate functions connected solely to the weakening of the military forces of an enemy. Indeed, both the Russian and Ukrainian statements use the phrase “military cargo.” However, the Russian statement has been made explicitly in connection with the end of the Black Sea Grain Initiative, the cessation of the functioning of the maritime humanitarian corridor, and the Russian targeting of civilians and civilian infrastructure in Ukrainian ports. The objective of such actions clearly extends beyond merely weakening the enemy’s military forces. Indeed, historically, the regimes of contraband and the right of search and visit coupled with the regimes of blockade and prize law have been intertwined with the practice of economic warfare, a practice which has as its aim the targeting of the civilian population in addition to an enemy’s military forces.

The practice of economic warfare is itself intrinsically linked to the debate on whether a target can become a military objective simply because of its contribution to “war-fighting,” and “war-supporting” functions, or whether it can extend to “war-sustaining” functions as well. The majority of States in the international community squarely rejects the notion that an object can be rendered a military objective merely because such an objective generates revenue which contributes to the enemy’s warfighting effort. This has been widely acknowledged in scholarship and by multiple expert groups as well. The San Remo Manual, the HPCR Manual on Air and Missile Warfare, the Tallinn Manual on cyber operations and most recently, the 2023 Newport Manual on the Law of Naval Warfare have all rejected this proposition as well. Such a consensus should give rise to some reflection about the continuing validity of forcible methods of unrestricted economic warfare. Ironically enough, the United States has remained the most prominent advocate of the notion that “war-sustaining” functions can also convert a target into a military objective. Notably though, this stance has a very short provenance even in the United States, and possesses an extremely shaky historical and legal grounding which has been comprehensively rebutted (p. 448-451) in academic scholarship.

The Relationship of the Law of Naval Warfare to General International Law

This situation brings into stark contrast the fundamental assumptions that inform much of the law of naval warfare. The law of naval warfare engages in a balancing act between the competing interests of the belligerents who wish to defeat the enemy and the interests of neutral States who wish to guarantee their merchant vessels the freedom to engage in maritime trade. Under the law of naval warfare, as classically understood, the right of the belligerents to conduct hostilities has been more important than the economic and commercial rights of neutral States. However, is this still a valid understanding today? Proponents can be found for both views. James Kraska suggests that a belligerent’s right to conduct hostilities is more important than the right of neutral States to trade with the belligerents. Andrew Clapham would suggest the opposite.

Much of the basis for these differing views boils down to a divergence of opinion on whether in the post-Charter world, international law can still “recognize a state of war which triggers the application of the laws of war in the traditional way.” As outlined by Churchill and Lowe in their 1999 edition of the Law of the Sea (p. 422-423) there exist two approaches to this issue. The minority views suggests that when force is used on a large enough scale, then it is regulated by the laws of war and neutrality (in the traditional way). However, the majority view holds that “all actions under the laws of war and the law of neutrality must now seek their justification” (under a UN Security Council mandate or Article 51 of the UN Charter).

Under the traditional understanding of the law of naval warfare, a neutral ship’s right to freedom of navigation is subject to a belligerent’s right of visit and search. The concept of “belligerent rights” is one whose origins lie in the pre–UN Charter era. This body of law was largely framed in the period between the mid-19th century to the early 20th century. This was a time when war was thought of as a meta-juristic phenomenon and an era when engaging in the unfettered use of force was considered an attribute of statehood itself. However, the post-Charter period is a fundamentally different one. In an international order characterized by the prohibition of the use of force by States in their international relations, force can be lawfully used only pursuant to the mandate of the United Nations or as part of a State’s right to self-defense.

Article 31(3)(c) of the Vienna Convention on the Law of Treaties requires that an act of interpretation take into account any relevant rules of international law applicable between the parties. This provision, which is a plea for systemic integration, merely asks that the interpretation of rules occurs “in the light of some comprehensible and coherent objective, so as to prioritize concerns that are more important at the cost of less important objectives.” (¶ 419, p. 86). Consequently, the most crucial issue when interpreting the law of naval warfare in relation to the UN Charter is whether the limitations on the use of force set out in Article 2(4) influences belligerent rights under that body of law. Specifically, must the body of law regulating hostilities between belligerents be reconciled with the notion of self-defense or must it not? The consequence of a combined reading must be to call into question the legality of indiscriminate search and visit operations and blockades against neutral ships. The need for a belligerent to ensure adherence with the requirements of necessity and proportionality makes it inconceivable to arrive at a different answer.

Wolff Heintschel von Heinegg has correctly opined that there is little evidence to indicate that the provisions of the UN Charter would impact the measures of economic warfare aimed at enemy ships and goods. However, he believed that this was not the case with respect to measures directed against neutral ships and goods. As early as the 1990’s, Heinegg remarked upon the tentative formation of a customary rule to the effect that neutral merchant ships cannot be interfered with if the official policy of the ship’s flag State prohibited the transfer of arms and war material to the belligerents.

 A large number of primarily Western States has adopted a stance of qualified neutrality and are currently actively transferring arms and war material to Ukraine. This stance may very well preclude their standing to claim an exemption from indiscriminate search and visit operations and blockades. However, this should not preclude the vast number of States whose policies do prohibit the transfer of arms and war materials to the belligerents from seeking such an exemption. These States are predominantly from the Global South. These are exactly the States that have had the least (or to be more accurate – nonexistent) role in shaping the law of naval warfare (which were all crafted in the pre-decolonization era). The food shortages that are now being caused by the fall in shipping traffic is negatively impacting the global south the most.

Concluding Thoughts

The law of naval warfare is a body of law which pre-dates the entry into force of the UN Charter. To hold that the regime of belligerent rights embodied therein is self-contained body of law would be to declare that international law merely comprises a series of fragmented specialist bodies of law rather than being a single, unified system. Ultimately, the question that deserves to be asked is, if the only legitimate object that States may endeavour to accomplish in war remains the weakening of the enemy’s military forces, then why may a belligerent be permitted to resort to a method of warfare that is essentially unlimited?


Himanil Raina is a PhD candidate and a Teaching Assistant at the Department of International Law at the Geneva Graduate Institute.


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