The Legality of the Use of Unmanned Maritime Systems under International Law

            Since Russia’s full-scale invasion of Ukraine on February 24, 2022, Ukraine has contended with both materiel and manpower disadvantages. To counteract Russian asymmetrical naval superiority in the Black Sea, the Ukrainian military has developed unmanned maritime systems, which can inflict damage at a relatively low cost to Ukraine. Ukraine has effectively sunk or severely damaged numerous Russian warships and other strategic targets, including the Russian guided missile cruiser Moskva, the corvette Ivanovets (a Tarantul class missile ship), a Bykov class corvette, the landing ship Caesar Kunikov, a high-speed patrol boat, and the Kerch bridge, which links Crimea to Russia.  In response, Russia has redeployed and dispersed the bulk of its Black Sea Fleet far from the Ukrainian coast and Crimea, allowing Ukraine to restart exports from its primary port of Odesa.

            The use of unmanned maritime systems is a relatively new development and, as such, its legality under international law is subject to debate. This article examines the legal framework that regulates the use of unmanned maritime systems and, in particular, whether Ukraine’s usage of these systems is legal under the Law of Armed Conflict and International Law.   

The unmanned maritime systems that Ukraine deploys fall into two categories: unmanned surface vehicles (“USVs”), of which the Magura V5 and the Sea Baby have been the primary two types identified; and unmanned undersea vehicles (“UUVs”), of which the Marichka and the Toloka are the primary two types identified. Ukraine operates its USVs by remote control via satellite, and are equipped with high definition night vision camera systems for navigation and targeting.They are each equipped with backup communications systems, allowing the person controlling the USV to remain in control even in the event of disruption. The USVs typically attack by navigating to the target and detonating the explosives on board. The Magura V5 is designed to strike warships at sea, whereas the larger Sea Baby is intended for stationary targets, such as ships at port and bridges. The Sea Baby has also been equipped to lay mines to target Russian naval ships navigating through the Black Sea. Individual USVs tend to do little damage, but multiple USV hits can sink a ship. The Economist estimates that Ukraine’s USVs have knocked out approximately ten Russian ships, while the Wall Street Journal speculates around two dozen Russian warships have been sunk or damaged.

            Ukraine’s UUVs are relatively new and public information about them is limited. Reporting has indicated that they are both remote-controlled and are equipped with sophisticated cameras, sonar, and hydrophone for navigation. Initial reports suggest the UUVs will be used in demining operations, and most likely to also attack enemy ships when operationally feasible.

            An analysis of USVs and UUVs can begin – but not end – with the question of whether these crafts qualify as “ships” or “vessels” (the terms are used interchangeably) under the United Nations Convention on the Law of the Sea (“UNCLOS”), and if so, whether they qualify as “warships.”  Under UNCLOS and customary international law, vessels are entitled to certain navigational rights such as the right of transit passage through international straits. If a vessel is further classified as a warship, that permits the vessel to exercise “belligerent rights” during wartime. Belligerent rights would include attacking enemy ships, enforcing blockades, and controlling neutral vessels in the vicinity of naval operations.

UNCLOS—perhaps the most informative source of international maritime law and to which both Ukraine and Russia are signatories—does not explicitly define “ship,” but it does require that each country set the requirements for the registration of ships in its territory, and that any such ship carry the flag of the applicable country. Warships, on the other hand, are explicitly defined under UNCLOS as a ship that belongs to the armed forces of the applicable country, have external markings reflecting the applicable country, are commanded by a commissioned officer, and are manned by a crew subject to regular armed forces discipline. With respect to the definition of “warship” (and the “ship” definitions that also have this requirement), it is not settled whether being remote-controlled satisfies the “manned” requirement.

Based on publicly available information, Ukraine has not flagged the USVs or UUVs as “ships” or “warships,” nor has it attempted to exercise any navigational rights on their behalf beyond operations in the Black Sea region. In addition, Ukraine’s USVs and UUVs are not “manned” in the traditional sense under UNCLOS as there is no crew or commissioned officer on board to control the ship.Given these facts, it is unlikely that, under current interpretations of UNCLOS, Ukraine’s USVs and UUVs would qualify as a “warship.” Although USVs and UUVs likely do not constitute warships, that does not mean that they are precluded from attacking Russian military targets. To determine whether USVs and UUVs can be used as lawful means of warfare, the context in which they are employed is paramount.      

            The primary sources of law governing the usage of weapons systems as lawful “means of warfare” are the 1949 Geneva Conventions, a series of international treaties establishing the Law of Armed Conflict between the parties to the treaties (which include both Ukraine and Russia as states parties), and specifically, Additional Protocol I to the 1949 Geneva Conventions (“AP I”) with respect to the usage of means of warfare in an international armed conflict. Additionally, the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (“San Remo Manual”) is a codification of customary international law governing naval warfare, and largely applies the principles of the Geneva Conventions to naval warfare.  “Means of warfare” are weapons and weapons systems that are capable of conducting an “attack,” which is defined under Article 49 of AP I as an offensive or defensive act of violence against an adversary.       Russia and Ukraine are involved in an active military conflict, and Ukraine is using USVs as weapons to target enemy ships and military infrastructure, which are classic examples of an “attack.”

            Under AP I and the San Remo Manual, in order to justify the use of USVs and UUVs (or any weapon or weapons system, for that matter) a country’s military must do the following:

• conduct legal review of new means of warfare prior to deployment;
• distinguish between military and civilian targets (including accepting surrender of targets where the surrender is evident to the attacker); 
• be capable of assessing proportionality (i.e., weighing the military advantage of an attack on a particular target against the attack’s expected collateral damage to civilians or civilian objects);   
• take all feasible precautions to prevent damage to civilians (including cancelling attacks if proportionality rule will be breached and provide effective advance warning if circumstances permit);  and
• have command accountability. 

            As a general matter, it is rare for a means of warfare to be considered illegal under international law per se. To be per se illegal, such a weapon would need to be incapable of complying with the requirements set forth above under any circumstances—a classic example of this would be a biological weapon, whose potential to spread uncontrollably renders it unable to distinguish between civilian and military targets. If a weapon is not per se illegal, its legality will depend on both the weapon’s characteristics as well as the particular circumstances of its usage. 

Ukraine’s usage of USVs and UUVs to target Russian military vessels and infrastructure suggests that Ukraine has developed these systems to comply with the principles set forth under the Law of Armed Conflict, specifically AP I and the San Remo Manual. In particular:  

• As a party to AP I, Ukraine is responsible for reviewing USVs and UUVs for compliance with AP I prior to deployment. There is no publicly available information regarding these reviews—countries do not typically publish these reviews for strategic reasons, and Ukraine would be understandably unwilling to disclose detailed information about new weapons systems to its enemy during wartime. Nevertheless, the fact that Ukraine otherwise appears to be making efforts to comply with relevant international law with respect to USVs and UUVs as described in this article suggests Ukraine has most likely conducted the required legal review of these weapons systems.
• Ukraine’s USVs and UUVs can distinguish between military and civilian targets because they are remote-controlled and equipped with sophisticated camera and navigation systems that allow their operators to identify military targets, and navigate them to avoid civilian vessels and infrastructure. 
• Ukraine’s USVs and UUVs are capable of fulfilling the proportionality requirement because their camera and navigation systems allow operators to get a complete picture of the target and surrounding area to identify the level of risk of collateral damage to civilians and civilian objects, as well as their relatively low payload reduces the risk of collateral damage. In addition, Ukraine’s USVs and UUVs have “redundant” communications systems that reduce the likelihood of remote control being disrupted, which allows the operator to maintain control of the system until the attack is completed and, if necessary, cancel the attack if circumstances change.   
• Ukraine’s USVs and UUVs also comply with the command requirement because they are under the control of human operators, and responsibility can be assigned to the operators and/or the operators’ commanding officers who ordered the attack.

            As noted above, Ukraine’s UUVs are more difficult to assess because they are relatively new and less is known about them, including the extent to which they have been used in the Russian war. However, the same analysis of the legality of USVs would apply to UUVs – that they would be permissible weapons systems under international law provided that Ukraine complies with the principles of AP I and the San Remo Manual as described above. 

            Additionally, the 1907 Hague Convention VIII (“Hague VIII”) and the San Remo Manual impose additional restrictions on waterborne explosives (mines and torpedoes) that require them to sink or be disabled after a certain time so they become harmless and are not a permanent hazard to civilian vessels. An additional related question has arisen concerning whether USVs would be considered “torpedoes” under international law and thus be regulated under Hague VIII. Ukraine’s USVs and UUVs share characteristics with a torpedo in that they travel through water to attack enemy targets. Nonetheless, Hague VIII is more than one hundred years old and was intended to protect against unsophisticated, non-guided weapons systems, such as torpedoes and mines, so its applicability is questionable. And unlike the traditional torpedoes that Hague VIII intended to protect against, Ukraine’s USVs and UUVs have advanced remote control and satellite guidance, and can be steered to avoid civilian vessels and infrastructure. Moreover, their “redundant” communications systems reduce the risk of an operator losing control of the USV or UUV and therefore unlikely that a USV or UUV would become a permanent hazard. While classification of Ukraine’s USVs and UUVs as torpedoes under Hague VIII as a matter of international law is questionable and unsettled, such a classification would provide an additional justification of their use under international law given that their usage, guidance systems, and control appear to comply with the conditions of permissible torpedoes under Hague VIII and the laws of warfare under the Geneva Conventions and San Remo Manual discussed above.    

Based on what is known about the USVs and UUVs – the nature of the weapons systems, and more importantly how Ukraine has deployed them in the war thus far – their usage in the reported circumstances appears to be in compliance with international law and the Law of Armed Conflict.

Authors: Dr. Gregory P. Noone and Sindija Bēta, PILPG, and Ropes & Gray

Conceptualizing IHL is a series of essays on various topics of international law limiting the use of violence in armed conflicts. These laws are grounded in the fundamental need to protect human dignity and alleviate civilian suffering during times of war

This material has been developed by the Public International Law & Policy Group for the Center for Civil Liberties.

The materials of this series are allowed to be published on other resources in whole or in part, provided that the authorship is indicated and an active hyperlink to the organization’s website is provided.

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