The use of new technologies in contemporary armed conflicts creates new challenges for international humanitarian law. In particular, this concerns the deployment of unmanned systems/vehicles (drones) [13]. Naval operations and actions against port infrastructure have not been an exception, involving the use of unmanned maritime systems/vehicles (drones) (hereinafter – UMS) and unmanned aerial systems/vehicles (drones) (hereinafter – UAS).

The scale of their use by Ukraine during the international armed conflict caused by the aggression of the Russian Federation against Ukraine allows us to conclude that unmanned maritime systems have evolved into a distinct category of weapons capable of inflicting significant damage on the adversary even under conditions of asymmetric force ratios and substantially limiting the operations of naval vessels [11].

The use of unmanned systems/vehicles must be assessed not only in the context of military strategy, but also through the prism of international humanitarian law, in particular Article 36 of the Additional Protocol to the Geneva Conventions of 12 August 1949 relating to the Protection of Victims of International Armed Conflicts of 8 June 1977 (Additional Protocol I).

In addition to the application of the general principles and norms of international humanitarian law governing the means and methods of warfare (including customary international humanitarian law and Additional Protocol I, subject to the reservation contained in Article 49(3) of Additional Protocol I), special rules applicable to armed conflicts at sea must also be taken into account [5], as set out in the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1992) [4], as well as in certain Hague Conventions of 1907 relating to naval warfare.

Article 49(3) of Additional Protocol I provides that “the provisions of this Section [Section I – General Protection against Effects of Hostilities of Part IV – Civilian Population of Additional Protocol I] 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.”

General rules of international maritime law must also be taken into account, particularly with regard to the right of third States to use international waters of the World Ocean for lawful purposes.

Unmanned maritime systems are actively used for reconnaissance operations, attacks on warships, naval bases and port infrastructure used for military purposes, as well as other objects meeting the criteria of a military objective under international humanitarian law (Article 52(2) of Additional Protocol I), such as the bridge across the Kerch Strait.

When employing any type of combat drones—whether aerial, ground-based, or maritime—all principles of operational international humanitarian law apply, in particular the principles of distinction, proportionality, and precautions in attack. Contemporary armed conflict combines elements of high-technology warfare and traditional warfare, and the international armed conflict between the Russian Federation and Ukraine demonstrates both the military and the legal dimensions of this issue [13].

It can be stated that Ukraine has complied with the principle of distinction in its attacks on Russian warships in Sevastopol Bay [2; 16], Novorossiysk and other locations (on 4 August 2023, during an attack on the Russian naval base in Novorossiysk, the large landing ship Olenegorsky Gornyak was damaged [1]; on the night of 31 January–1 February 2024, maritime drones attacked the Russian vessel Ivanovets [15]; on 5 March 2024, the Russian ship Sergey Kotov was sunk [12]), as well as in the attack on the bridge across the Kerch Strait [3]. The latter constitutes a dual-use object due to its use for the transportation of military cargo and dual-use goods [10], thereby making an effective contribution to military action and providing a definite military advantage to Russia. Accordingly, it fully meets the criteria of a military objective under Article 52(2) of Additional Protocol I and paragraph 40 of the San Remo Manual.

In contrast, the widespread use by Russia of “Shahed” kamikaze drones to strike civilian port infrastructure in Ukraine constitutes an example of a systematic violation of the principle of distinction in the employment of emerging weapons and amounts to a serious breach of international humanitarian law [6; 8; 9; 14]. A further example of such a violation is the attack carried out by the Russian Federation using unmanned aerial systems against grain silos in Izmail on 23 August 2023 [7], which represents a breach of the applicable methods of warfare.

It should be noted that, unlike unmanned maritime systems (UMS), which are currently operated under real-time operator control, unmanned aerial systems (UAS) more often fall within the category of automated unmanned systems programmed prior to launch. This excludes the possibility of (1) assessing the target during the непосредственной attack; and (2) cancelling the attack or changing the target in the event of altered circumstances or a change in the nature of the target.

These shortcomings are absent in operator-controlled UMS; however, their use may still entail risks that must be taken into account when planning an attack in order to comply with the fundamental principles of international humanitarian law, in particular the principles of precautions in attack and proportionality:

1. when planning attacks against military objectives located in naval bases and ports of the adversary, clear identification of the target and compliance with the principle of proportionality are essential;
2. when attacking warships or auxiliary vessels of the adversary in maritime areas, precise identification of the military objective must be ensured;
3. special requirements of international law applicable to the naval theatre of warfare must be taken into consideration;
4. when attacking dual-use objects, the possibility of dynamically changing circumstances must be taken into account. Particular attention should be paid to verifying any change in circumstances immediately prior to the attack in order to ensure compliance with the principle of proportionality and the taking of necessary precautions;
5. appropriate measures must be envisaged in the event of loss of control over a UMS, taking into account the potential risk to merchant vessels, civilian objects, or civilians in the event that an uncontrolled system reaches the shore.

In our view, when unmanned maritime systems (UMS) are employed in maritime areas used for commercial navigation or adjacent to States that are not parties to the international armed conflict, it is advisable to take measures to provide general notification to the International Maritime Organization, coastal States, and other participants in commercial shipping regarding the potential use of UMS in such regions.

Thus, the use of emerging technologies such as UMS and UAS in a contemporary international armed conflict creates new opportunities for achieving military objectives, while simultaneously posing challenges to compliance with the fundamental principles of international humanitarian law governing the conduct of hostilities.

Ukraine demonstrates adherence to these principles in the conduct of hostilities through the use of unmanned systems, in particular in attacks against objects with confirmed military status, such as Russian warships, Russian naval bases, and the bridge across the Kerch Strait. In contrast, the Russian Federation demonstrates systematic and serious violations of international humanitarian law, in particular the principle of distinction, through the use of kamikaze drones to strike civilian port infrastructure in Ukraine, such as grain silos and other civilian port facilities, which may constitute war crimes.

List of References

1. Attack on the Russian Fleet Base in Novorossiysk: The Ship Olenegorsky Gornyak Damaged – BBC News Ukraine. BBC News Ukraine. 04 August 2024. Available at: https://www.bbc.com/ukrainian/news-66403178 (accessed: 18 March 2025).
2. Video of the Underwater Drone Attack on Russian Ships in Sevastopol, 2022. YouTube. Available at: https://www.youtube.com/watch?v=O0glD242Znw (accessed: 14 March 2025).
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