The Warship’s Remote Operator: Who Is the Captain Now?

The U.S. Navy has begun employing “ships” that can be operated remotely, raising questions about responsibility and control.

Unmanned surface vessels (USV) Ranger and USV Mariner, 2023 (US Navy Photo by Mass Communication Specialist 2nd Class Jesse Monford.

Editor’s Note: Although the authors of this piece are officers in the United States Navy, the opinions and assertions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the United States government, the Department of Defense, or the Department of the Navy. The analysis presented here stems from their academic research of publicly available sources. 

On Jan. 16, four of the U.S. Navy’s unmanned surface vessel (USV) prototypes (meaning a vessel that can operate without a human crew) recently returned from operations in the Western Pacific. Over several months in late 2023, these vessels—named Ranger, Mariner, Sea Hunter, and Sea Hawk—made port calls to Japan, Guam, Australia, and other nations, as part of a multilateral exercise to test the operation of unmanned systems. According to the Navy, this deployment was focused, at least in part, on command and control. During their time at sea, Navy researchers tested several ways to control the vessels using various configurations of operators and consoles—both from ashore at an Unmanned Operations Center in Port Hueneme, California, and at sea from another U.S. Navy ship in the region. Ranger and Mariner in particular were “testing more advanced autonomy features under the supervision of a civilian crew which [was] under orders to observe, but not interfere unless absolutely necessary.”

The advent of USVs for military use has raised important questions, such as: Does international law prohibit or restrict the use of USVs in peacetime or in conflict? What body of law, established or novel, should govern their use? Perhaps most importantly, who is responsible for missteps or miscalculations in the use of these vessels? Among these inquiries—which are largely the basis of observers’ and policymakers’ discussions—two central questions remain mostly unexamined. First, would the presence of a civilian master mariner aboard a U.S. military USV affect the vessel’s status under international law? Second, how would the ability of this civilian—or any human aboard the ship—to override a USV’s preset orders or parameters impact the remote commanding officer’s responsibility for any wrongful conduct? 

Put simply: Who is the captain now? 

Unmanned Maritime Systems

USVs are a subset of unmanned maritime systems (UMSs). At present, UMSs can operate on either the surface or underwater, may be capable of fully autonomous operations, and/or can be controlled from a shore-based operations center or nearby ship. In both Navy and commercial contexts, most unmanned flagged vessels are tele-operated—meaning operated remotely by a human who is not physically located aboard the vessel—rather than fully autonomous. However, as technology improves, UMSs and USVs may become increasingly autonomous as technologies and trust in these systems improve. As Navy leaders have expressed, unmanned or optionally manned vessels will likely be key to how the Navy’s fleet will operate in the future. (In fact, the Navy just established a Robotics Warfare rating “to support current and future autonomous unmanned systems (robotics) employment”). 

The development of UMSs requires a more modern legal analysis centering on whether and to what degree international law mandates that USVs be “manned,” and by whom, to receive the rights and obligations that a traditional, manned vessel may receive (such as sovereign immunity). This is not exactly an issue of first impression in either the international or domestic realm: aerial dronesweapons incorporating advanced algorithms, and even ground vehicles have provoked heated debate on this matter. But those legal analyses do not exactly fit here, as a vessel—or a USV—is not a weapons system itself but, rather, a platform for weapons such as missiles, torpedoes, and mines. It should, therefore, be analyzed through that legal paradigm. 

These analyses become even more complex when considering that both the USVs Ranger and Mariner, according to at least two sources, have a civilian master mariner on the bridge of each vessel. (The bridge is the room from which the ship is commanded.) A civilian mariner is a sailor who holds a license from a maritime authority to hold a senior, officer-level position aboard a ship, and a master marine holds the highest qualification: They can serve as the master, or the captain, of a merchant ship of any size and type. 

With these definitions in hand, consider the unanswered questions concerning how the presence of civilians aboard an unmanned vessel may affect its legal status, whether it should or needs to be classified as a warship, the vessel’s rights and obligations under international law, and a military commander’s responsibility for violations of international law principles in the use of that vessel.

Vessel Classification and Legal Status

Many factors go into determining whether USVs fit into preexisting classifications of vessels. The classification of a vessel determines the rights and obligations tied to it: for example, whether it has sovereign immunity, whether it can be used to exercise belligerent rights, or the types of passage it can conduct in certain waters. At the risk of being too simplistic, vessel classification centers on two characteristics: who is on it and what it is being used for. Under peacetime law of the sea, the two classifications would be commercial vessels and vessels exclusively used for noncommercial government service. However, during periods of conflict, and for purposes of this piece, vessel classifications include civilian vessels, warships, and auxiliaries. The rights and responsibilities of each of these three classifications change depending on whether the vessel is associated with a neutral or belligerent state

Importantly, not all of the following terms and their corresponding legal statuses are universally agreed upon. This includes the very definition of a “ship” to what “under the command” necessitates. To be sure, a “ship” can be defined rather broadly, as to include a bathtub, but not so broad as to include a mere glider or float. Moreover, these legal definitions were developed over much of the 20th century, during a period of time when unmanned craft were still unfathomable. As such, although historically based, the following terms have not been updated for modern technological developments and conflict. This underlies the vigorous debate and related uncertainty surrounding their application to unmanned vessels. 

What Is a Vessel or Ship?

A “vessel,” to start, is commonly defined using the International Maritime Organization’s (IMO’s) definition of “every description of water craft … used or capable of being used as a means of transportation on water.” A vessel must have a master who is assigned responsibility for the vessel under a state’s jurisdiction. The term “vessel” is often used interchangeably with the word “ship.” Although there is no uniform definition for a “ship” under international law, historical practice and custom required humans on board to fulfill due regard and other obligations. In other words, ships needed to be manned

Under the United Nations Convention on the Law of the Sea (UNCLOS), a flag state must ensure that each of its flagged ships is “in the charge of” a master and officers with the appropriate qualifications (such as navigation and communications). Moreover, a ship’s crew must have the qualifications and be of a size appropriate for the specific ship. There is a scholarly debate, however, about whether the phrase “in the charge of” can be constructively interpreted to include a remote, shore-based team for unmanned vessels. 

What Is a Warship?

The peacetime definition of a warship, as captured in UNCLOS, is “a ship belonging to the armed forces of a State” with the following three characteristics: it (a) bears external markings that distinguish its character and nationality, (b) is under the command of a commissioned officer, and (c) is manned by a crew under the purview of the armed forces. Warships, along with other vessels used exclusively for the time being on noncommercial government service, are granted sovereign immunity during peacetime. 

Warships may engage in belligerent acts during periods of armed conflict. Although there is no defined list of belligerent rights, they are widely understood to include kinetic strikes; visit, board, search and seizures of other ships; laying mines; amphibious operations; and blockades. 

The United States’s policy on unmanned or partially manned warships is articulated most clearly in the Commander’s Handbook on the Law of Naval Operationswhich was last updated in March 2022. It provides that there “is no requirement the commanding officer or crew be physically on board,” meaning that the warship may be remotely commanded, crewed, and operated. 

What Is an Auxiliary?

Similar to warships, auxiliary vessels are owned and operated by a state’s military. The key difference is that auxiliary vessels are commanded by civilian masters rather than commissioned officers. In addition, while auxiliary vessels also receive sovereign immunity during peace and may be the subject of attack in armed conflict, they take on limited roles to directly support military forces during conflict (for example, refueling and replenishing warships being used in conflict). Traditionally, the U.S. Navy employs civilian mariners through the Military Sealift Command, to master and man vessels in an auxiliary capacity, delivering military personnel and materiel for the military. 

How Are Unmanned Systems Classified? 

Against the definitions of vessel, warship, and auxiliary outlined above, many have questioned whether a USV can even be classified as a warship given that the vessel’s commanding officer and crew may not be physically located aboard the ship. 

Generally speaking, a UMS is “either autonomous or remotely navigated” and may “operate independently as a ship” or be launched. When a UMS is flagged as a ship and thus becomes a USV, it “may exercise the navigational rights and freedoms and other internationally lawful uses of the sea.” From the perspective of the IMO, there are four degrees of autonomy for an unmanned ship:

  • Degree 1: The ship has automated processes and decision support, but seafarers are on board to operate and control the systems and functions.
  • Degree 2: The ship is remotely controlled and operated from another location, but seafarers are on board.
  • Degree 3: The ship is remotely controlled and operated from another location, and no seafarers are on board.
  • Degree 4: The ship is fully autonomous. 

As stated above, a warship must be under the command of a military officer and manned by a crew also belonging to the state’s military. The U.S. perspective is that as long as the USV can be remotely controlled or operated, the “command” and “manning” requirements of UNCLOS are satisfied. 

According to some commentators, a new legal classification should be developed for USVs rather than having states classify them as warships, let alone vessels. Within this area of thinking, one issue with classifying UMSs as “vessels” within the existing framework is that doing so requires them to abide by historic legal requirements, such as having proper lighting while on the surface per the Convention on the International Regulations for Preventing Collisions at Sea, a peacetime regulation. This, in turn, may cause developers to design UMSs in a way that avoids certain vessel classifications. 

We respectfully disagree. As an initial point, law of the sea scholarship does not always do an excellent job of making a distinction between peacetime law of the sea and wartime law of the sea definitions and obligations, often merging and glossing over distinctions. In the matter of warships, the definition of “warship” in Article 29 of UNCLOS (a peacetime treaty) came from Article 3 and 4 of Hague Convention VII of 1907 (a law of war treaty). The peacetime definition of “warship” is now generally accepted as customary international law. The command and manning provisions in the Hague Convention, repeated in treaties, treatises, and manuals since, were included not to ensure the presence of humans aboard the vessel but, rather, to require that the warship be subject to state oversight and military discipline. 

Similarly, Article 29 of UNCLOS aims to ensure that vessels afforded sovereign immunity protections under the law of the sea are under proper control and conducting appropriate noncommercial business to warrant that treatment. Their shared purpose is trifold: (a) attach state responsibility to the activities of vessels with special rights and obligations under the law, (b) allow others to understand the extent of its lawful conduct, and (c) distinguish these vessels from other vessels (for example, merchant or civilian vessels). Even though UNCLOS is a peacetime treaty and does not address belligerency, interpreting Article 29 to incorporate USVs allows USVs to be considered government ships, within its meaning, and thus receive certain protections such as sovereign immunity. 

It may be, therefore, in the best interest of the international community to incorporate USVs—when they are intended for or used to engage in military activities—into the traditional law of the sea and law of war framework for warships, thereby confirming state responsibility for their actions. Although some commentators find it “difficult” to interpret or stretch the traditional warship standard to include a USV, there is good reason to “stretch the notion of command” and manning to include remote control or oversight. International maritime custom, regulations, and treaties should be interpreted with their purposes in mind, rather than solely textually. This includes customary law of war, as well as UNCLOS: It should be regarded as a living instrument whose context and purpose are responsive to new technologies. Therefore, it must be interpreted from a contextual, pragmatic, and functional perspective. 

After all, as put by Judge Anthony Amos Lucky in an opinion for the United Nations International Tribunal for the Law of the Sea, “the law of the sea is not static.” States ought to be compelled to control or be held accountable for the safe navigation, uses of force, and other actions that USVs are used to execute. Ultimately whether a UMS is a “vessel” or “ship,” and thus a warship within international law, may matter less where there is already broader latitude under international law to use military devices that do not constitute “warships” at sea. Nevertheless, incorporating USVs into the internationally developed construct of a warship is likely the most effective mechanism to accomplish the goal of state responsibility. 

The Remote Operator

When turning to address the question of the “remote operator,” the international community ought to view her as a “master” of an unmanned vessel if she bears responsibility for the vessel under a state. Now, whether a remote operator is the functional equivalent of an onboard ship’s master in terms of actual ability to command the vessel is a separate question. Depending on the vessel’s design, the remote operator may be as in control of the vessel as a person aboard, for example by controlling operations such as the speed, direction, and location of the vessel. If the powers are functionally similar, then the answer of command is simple: The remote operator is “in the charge” of the vessel and is, therefore, the master. But international law’s requirement that there be a master of a vessel for it to be classified as a ship ultimately boils down to responsibility for that vessel: International law cares primarily about whether someone can be held responsible

Extend this analysis to fully autonomous vessels: The master is whoever the state appoints to be the master. Her involvement or lack thereof is a question of risk: Ultimately she will be responsible for what occurs to the vessel or what actions she directs the vessel to take, and the state will be responsible for licensing her and for the safe navigation of its flagged vessel. This functions just as it does for the commanding officer of a manned vessel, who will be held responsible if that vessel runs aground or hits another ship

Who Is the Captain Now?

With the news reports surrounding USVs Mariner and Ranger, how would a civilian merchant mariner captain affect a warship’s status? As it turns out, pretty significantly. 

As stated above, naval auxiliaries can be commanded and manned by civilians; assigning a civilian merchant mariner as captain then could place a USV within the auxiliary realm, which in turn affects the vessel’s rights and obligations under international law. This reflects the traditional law of war requirement that states “ensure belligerent rights at sea are exercised on their behalf by lawful combatants, and combatants use offensive force only as necessary, with distinction, proportionality, without causing unnecessary suffering, and within the bounds of military honor, particularly without resort to perfidy.” The traditional ways to meet these requirements meant that (a) a ship used to conduct belligerent acts must first be commissioned as a U.S. ship and (b) the civilian captain must be replaced by a commissioned naval officer. Then, and only then, the vessel could be categorized as a warship and be used to engage in belligerent activity. 

A counterargument here is that, despite the civilian master being physically present aboard the vessel, there is still a military officer commanding the ship, and more importantly the belligerent activities, from a distance. This, in turn, further convolutes the problem: It raises the questions of how attenuated the military commander can be for a USV to be categorized as a warship and whether the civilian master’s physical presence on the USV supersedes the naval commanding officer’s ability to exercise command and control remotely. 

As an added complicating factor, news reports claim that the Navy’s USVs come with “a large red button” (which, if pressed, stops the ship and returns manual control to the captain within seconds). This fail-safe mechanism is also contemplated for commercial USVs. In April 2023, in the Second Session  of the Joint Working Group on Maritime Autonomous Surface Ships (MASS), an IMO scoping exercise set out the following:

  • There should always be a human responsible for the ship, regardless of the level of autonomy of the vessel.
  • The human master does not have to be on board.
  • The ship need not be manned. 
  • The human master should always have the means to intervene. 
  • A human master may be responsible for multiple unmanned vessels at the same time. 

These five concepts, especially “means to intervene,” if adopted by member states in a binding instrument, would indicate that a MASS must have a fail-safe, akin to the large red button, that would allow a human to override the function or action of any USV, regardless of its designed degree of autonomy. 

Use of this button purportedly forces the ship to stop everything it is doing and returns all control back to the manual user on board the ship. It would be even harder to argue that a ship’s command and control is still within full control of the remote military commanding officer if the red button override were available to the onboard civilian master. 

But as stated above, the degree of control does not undermine the ultimate conclusion of state and individual responsibility. A ship—even autonomous—by itself does not unsafely navigate, wound, or kill. At some point, a human made a decision to (a) create the ship (b) for an intended purpose, (c) set that ship’s parameters of operation, and (d) launch that ship (e) to accomplish that purpose. And that decision was made by the state and a human, or a set of humans, who were delegated the authority to make that decision. Thus, the foundation of responsibility lies with the person, and it is the persons, not vessels, who have rights and obligations under the law of war. As echoed in Thucydides, “Men make the [state] and not walls or ships without men in them.” 


Much of this debate stems from uncertainty about these new technologies and whether the quality of a ship being manned or not changes the accompanying rights and responsibilities of that ship. If a state ever wants an unmanned system to avail itself of the rights of a warship, while capitalizing on the system’s “decision speed and lethality,” then the state must also be prepared to take on the accompanying responsibilities for its actions. 

The preoccupation with the “remote operator” and “red button” is a manifestation of an understanding that the locus of the law of rights and obligations at sea rests at all points where the human decision-maker is involved. No matter how attenuated the remote operator’s control is—either through a civilian captain or a large red button—she is the one responsible for the rights, obligations, and any violations of international law, including the law of war. 

Manal CheemaAriel Sarandinaki, Published courtesy of Lawfare

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