Uncrewed systems (UxS) serve as an integral part of the naval force structure and their use will likely increase during this century.[1] There are pressing law and policy questions related to UxS that the US Department of Defense and US Department of the Navy will have to answer as they continue to expand the use and development of such rapidly evolving systems. New technologies provide operational advantages through improved uncrewed capabilities, but legal and policy questions about the appropriate design and use of these systems remain, especially given the spread of UxS across the globe. This article examines specific legal questions affecting the Navy’s use of maritime surface UxS, including why defining UxS is critical to ensuring their appropriate use and governance, and for understanding how these systems are treated legally, depending on whether they are considered ships or vessels. This article is intended to support the Navy’s Unmanned Campaign Framework, the Science and Technology Strategy for Intelligent Autonomous Systems, and US and international uses of maritime UxS to combat threats.[2]

Very few laws exist that were written specifically for UxS; thus, many of the laws that apply to UxS are problematic because they were intended for platforms with a crew. For example, how could a UxS carry out the duty to render assistance to people at sea? How would safety regulations such as look-out requirements be managed by an uncrewed platform? Rational and often time-tested requirements that apply to crewed vessels become questionable or untenable in the context of UxS, pushing the interpretation, and in some cases, the applicability, of the law beyond usefulness. Furthermore, even if there is an agreement on how the law applies to UxS, the systems’ technology continues to change rapidly, and can be expected to evolve faster than the law.

In addition, not all states are signatories or members to the treaties that govern crafts in the maritime environment. For example, while the United States has taken part in negotiations for the UN Convention on the Law of the Sea (UNCLOS),[3] it has not signed or ratified the treaty.[4] However, the United States does consider many provisions of UNCLOS to be customary international law, including those “provisions concerning traditional uses of the ocean.”[5] The acceptance of UNCLOS provisions as customary international law—by the United States and other countries—is significant when applying the treaty to new uses of the ocean such as UxS.

This article highlights the current understanding of how certain maritime laws and regulations currently apply—or do not apply—to maritime surface UxS, and the uncertainties that remain, under treaties as well as customary international law.

A Question of Definition

Legal analysis of maritime surface UxS must begin with defining the systems. The foundational question of whether an uncrewed platform is a vessel is debated among legal scholars and is particularly important with regard to the rights and responsibilities authorized under UNCLOS and customary international law, including the freedom of navigation (also called freedom of transit) and sovereignty in the sea.[6]

UNCLOS does not officially define the terms “vessel” and “ship.” The International Maritime Organization (IMO) is considering rules to address this issue. If common definitions can be identified, then an argument can be made for applying customary international law to these uncrewed systems—i.e., if there is global consensus on the definitions of these terms, then a common definition of UxS may be reached.[7] In the absence of an international agreement, however, the current definitions that nations use for “vessel” and “ship,” and whether UxS are included in those definitions, will influence the definition of UxS that the IMO establishes. To determine whether there is a common definition of UxS in use, the authors focused on those used by the Five Eyes (FVEY) countries (Australia, Canada, New Zealand, the United Kingdom, and the United States), since these countries are already incorporating UxS technology into their fleets and may exert political influence internationally as these issues move toward resolution.[8]

Complexity of Defining UxS: Vessels versus Ships

Ships and vessels are referred to interchangeably in UNCLOS and lack formal definitions. “Vessel” has been defined in other internationally accepted policies; for example, the Convention on the International Regulation for Preventing Collisions at Sea (COLREGS) defines a vessel as including “every description of watercraft, including non-displacement craft, wing-in-ground-effect (WIG) craft and seaplanes, used or capable of being used as a means of transportation on water.”[9] Similarly, the US Code defines a vessel broadly in Title 1 as “every description of watercraft or other artificial contrivance used, or capable of being used, as a means of transportation on water.”[10] Even in the same code of law, there can be ambiguity regarding the distinction between a vessel and a ship. In the United Kingdom, the Merchant Shipping Act of 1894 defines a vessel as including “any ship or boat, or any other description of vessel used in navigation,” circularly using the term “vessel” in its own definition.[11] The more recent Merchant Shipping Act of 1995 does not include a definition of “vessel.”[12]

The term “ship” is not defined in UNCLOS but is defined in the International Convention for the Prevention of Pollution from Ships (MARPOL). MARPOL broadly defines a ship as “a vessel of any type whatsoever operating in the marine environment.”[13] In addition, each FVEY country has a definition of “ship.” However, neither of Australia’s main governing maritime policies, the Navigation Act of 2012 and the Marine Safety National Law Act of 2012, contains a definition of “ship.”[14] The Australian Shipping Registration Act of 1981 defines a ship as “any kind of vessel capable of navigating the high seas.”[15] Additionally, the Canada Marine Act, a regulation administered by the government’s commercial regulatory body, defines a ship as “every description of vessel, boat or craft designed, used or capable of being used solely or partly for marine navigation, whether self-propelled or not and without regard to the method of propulsion, and includes a sea-plane and a raft or boom of logs or lumber.”[16] Finally, the New Zealand Maritime Transport Act of 1994 defines a ship as “every description of boat or craft used in navigation, whether or not it has any means of propulsion.”[17]

With these foundational definitions in mind, the discussion moves to whether the United States has defined UxS as ships or vessels. In the 2022 Commander’s Handbook on the Law of Naval Operations, UxS are described as having the ability to “operate independently as a ship” and to “exercise any internationally lawful use of the seas.”[18] Thus, according to the Commander’s Handbook, the United States considers UxS as ships in at least some circumstances and, in accordance with the US position that most provisions of UNCLOS are customary international law, the UxS will fall under the governance of UNCLOS and other relevant laws. Additionally, the US Navy Sovereign Immunity Policy asserts that state-owned ships used on “government non-commercial service are entitled to sovereign immunity.”[19] Using this policy, UxS that engage in government non-commercial service would be considered sovereign immune craft, solidifying the position that the sovereign rights afforded to conventionally crewed ships under UNCLOS also apply to UxS.

Similarly, the United Kingdom’s policy describes how UxS fit into the existing UNCLOS framework. An International Relations and Defence Committee meeting on UNCLOS and modern uses of the sea concluded that, if UxS technology meet the given safety requirements for conventionally crewed ships, UxS should be considered as ships and given the associated rights.[20] In 2021 alone, the United Kingdom registered 23 UxS as vessels.[21] In its Maritime 2050 Strategy, the UK Department for Transport indicated that it views UxS as both ships and vessels, and capable of being registered as such.[22]

The Australian Maritime Safety Authority has consistently referred to UxS as vessels and has stated that “currently, these vessels are subject to the same regulatory framework as other vessels, including for survey standards and crewing requirements.”[23] Transport Canada has created a policy on the “Oversight of Small Maritime Autonomous Surface Ships.”[24] Even the title of the policy refers to the systems as ships, indicating that they will be legally treated as such. Additionally, in a 2002 court case regarding an uncrewed submersible device, a Canadian federal court applied the definition of “vessel” very widely, determining that the physical presence of a crew on board is not necessary for a waterborne craft to be classified as a vessel.[25] Finally, New Zealand issued an Interim Technical Note in 2020 that consistently refers to UxS as ships and provides viable pathways for registration, indicating New Zealand’s view that UxS fall under its definition of “ship.”[26] The document acknowledges that UxS do not meet certain crewing and watchkeeping requirements laid out in other policies and regulations, in which case ship owners are able to apply for exemptions that will allow their UxS to be registered.

FVEY countries are setting a precedent to apply specific terms to UxS, giving the systems the same inherent rights and responsibilities to abide by as conventionally crewed vessels under UNCLOS.

While it is still debated whether UxS fall under the legal definition of ship or vessel, FYEY countries have made their interpretation of the law clear in policies that include UxS as ships in at least some situations and by specifically registering UxS as ships. FVEY countries are setting a precedent to apply specific terms to UxS, giving the systems the same inherent rights and responsibilities to abide by as conventionally crewed vessels under UNCLOS. While this may indicate progress toward a globally recognized definition of UxS, there is not yet enough commonality to establish a foundation for a definition of UxS as vessels under customary international law.

Maritime Surface UxS as Vessels: Legal Analysis

As noted above, the US position indicates the acceptance of UxS as ships: The Commander’s Handbook on the Law of Naval Operations from 2022 states that “unmanned maritime systems may be used to exercise any internationally lawful use of the seas” including, but not limited to, the following uses:

1. Intelligence, surveillance, and reconnaissance

2. Mine countermeasures (MCM)

3. Antisubmarine warfare

4. Surface warfare

5. Inspection/identification

6. Oceanography.[27]

This position is significant; if UxS may exercise any lawful use of the sea, then those systems are also held to the same level of responsibility as mariners and crewed vessels. Most of these responsibilities are either codified in international conventions or accepted as customary international law—and were written in a human-centric way.

Therefore, once an uncrewed vessel is determined to be a ship, UNCLOS and other conventions apply, especially related to matters of safety and the requirement to meet certain situation-specific maritime duties. Maritime vessels are required to comply with international regulations for safety, such as fulfilling look-out requirements, providing due regard to other vessels; and rendering assistance in emergency situations. The analysis that follows shows how these requirements may be applied to maritime surface UxS and what questions still remain.

Look-out and Safety Requirements

The IMO established COLREGS to define the navigation rules to be followed by vessels at sea in order to prevent collisions. However, the regulations were designed for crewed vessels, not UxS; they depend on the presence of a crew to carry them out, so there is concern about whether COLREGS can be applied to UxS. Particular concern has been raised about Rules 2, 5, 8, and 18:[28]

Rule 2 covers the responsibility of the master, owner and crew to comply with the rules. . . .

Rule 5 requires that “every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.” . . .

Rule 8 covers action to be taken to avoid collision. . . .

Rule 18 deals with responsibilities between vessels and includes requirements for vessels which shall keep out of the way of others.[29]

There are many rules under COLREGS, including Rule 5’s look-out requirements, that “sometimes necessitate subjective deviations in accordance with the vessel’s circumstances or a captain’s experience.”[30]

The understanding of “see” and “hear” has expanded to include seeing via radar and hearing through speakers.

It is clear that COLREGS anticipates that the vessel will be crewed and will have a human look-out who can see and hear; this requirement has been, at least traditionally, met by a sailor on the bridge. The understanding of “see” and “hear,” however, has expanded to include seeing via radar and hearing through speakers. With this expansion of understanding, it is reasonable to consider that technology used on maritime surface UxS may meet this requirement with a remote operator as a look-out.

Designers and manufacturers of autonomous technology (whether vehicles, aircraft, or maritime vessels) argue that the risk of incidents with UxS is lower because of features such as advanced perception and collision avoidance technology.[31] In addition, crews already rely on autonomous systems onboard maritime vessels, not by seeing or hearing oncoming vessels from the bridge, but by receiving such information from a shoreside control station or second vessel. With this reliance on technology already in place, it may be reasonable to trust technology rather than rely on the traditional COLREGS standards that were written at a time when the only option was a human look-out.

As noted, however, the law will move more slowly than the technology and, without clear guidance to the contrary, the expectation will be that the human-centric standards will apply. In this vein, courts will rely on precedent that indicates that “overreliance on technology will not satisfy the principles of good seamanship.”[32] Thus, as a look-out, a remote operator or the actions of an autonomous or semi-autonomous vessel will be held to the same standard as a look-out on a crewed vessel.

Due Regard

Exercising certain rights in the maritime environment is not without limitations. When an uncrewed system operates in another coastal state’s Exclusive Economic Zone (EEZ), the system must abide by UNCLOS Article 58, Paragraph 3, which limits the system’s freedoms to those that maintain due regard for the sovereign coastal state. Specifically, it affirms that “States shall have due regard to the rights and duties of the coastal State and shall comply with the laws and regulations adopted by the coastal State.”[33]

Due regard has been described as allowing for the accommodation of competing interests by balancing states’ freedom of action with the necessity for self-restraint.[34] In other words, states must balance their freedom of action and claims of jurisdiction against the freedoms and claims of others. For example, if an uncrewed system is conducting military surveillance in an area, due regard requires that the surveillance will have no or little impact on the coastal state’s economic and environmental rights. Furthermore, any impact should involve an appropriate balancing of competing rights. A balance often is struck when the vessel and the coastal states have conflicting rights. Due regard applies to both UxS as well as the coastal state—i.e., the coastal state also must demonstrate due regard for UxS while they are operating in the state’s EEZ.[35]

In the context of UxS, what level of due regard can be provided? Not surprisingly, there is no clear international standard; however, there is general agreement that due regard applies whether or not a vessel is crewed.[36] Because UNCLOS does not define due regard, it is determined on a case-by-case basis. The International Tribunal for the Law of the Sea has described a similar standard, due diligence, as “a variable concept. It may change over time as measures considered sufficiently diligent at a certain moment may become insufficient in light of, for instance, new scientific or technological knowledge. It may also change in relation to the risks involved in the activity.”[37]

In a 2011 case regarding the former Yugoslav Republic of Macedonia v. Greece, the Tribunal “granted the states concerned a wide margin of appreciation to comply with the due regard obligation, but at the same time, it observed that it requires in any case negotiation and cooperation between themselves.”[38] This approach was confirmed in the Bay of Bengal Maritime Arbitration in 2014 concerning due regard, explaining that “it is for the Parties to determine the measures they consider appropriate in this respect, including through the conclusion of further agreements or the creation of a cooperative arrangement.”[39]

These decisions offer a glimpse into how due regard may be applied in relation to UxS. As vessels, UxS have the same rights and obligations in maritime zones under UNCLOS as crewed vessels. Therefore, they both owe and are owed due regard. Some examples of such due regard may be clear; for instance, UxS must not inhibit navigation of other vessels or operate in such a way as to violate the rules of the coastal state. At the same time, the coastal state (or another state’s vessel) may not seize UxS in violation of UNCLOS or other international laws, whether the UxS are remotely controlled or autonomous.[40] The question remains about activities that fall between these two ends of the spectrum, but the Tribunal’s decisions indicate that the determination will be on a case-by-case basis, taking into account the circumstances of the incident and precedent related to due regard of crewed vessels.

Duty to Render Assistance

International law imposes the obligation to save people in distress at sea as evidenced by its inclusion in several international conventions: UNCLOS (Article 98),[41] the International Convention for the Safety of Life at Sea (SOLAS) 27 (Regulation V/33),[42] and the International Convention on Salvage (Article 10).[43] Such clarity exists for crewed vessels, but there is uncertainty around how UxS would comply with the duty to render assistance.

It is important to clarify what qualifies as assistance in order to understand the potential duty of UxS. Assistance can vary, ranging from informative operations, such as launching a distress signal, to more dangerous activities, such as rescues of persons. The IMO interprets the duty to render assistance as requiring the master of a vessel to “do everything possible, within the capabilities and limitations of the ship, to treat the survivors humanely and to meet their immediate needs.”[44] However, under UNCLOS, this requirement is excused if the assistance can seriously endanger the ship, the crew, or passengers.[45] SOLAS adds that the mandatory duty is excluded if circumstances make assistance unachievable, unreasonable and/or unnecessary.[46]

The position of the United States is that being uncrewed does not preclude the duty of rendering assistance.

In applying such a duty to UxS, the position of the United States is that being uncrewed does not preclude the duty of rendering assistance.[47] However, Daniele Mandrioli notes two emerging issues: whether the responsibility to render assistance applies without an on-board master, and whether the responsibility to render assistance must be given to vessels designed to be uncrewed.[48]

Not surprisingly, under international law, there is not yet a clear statement or finding that a remote operator may be considered a master of the vessel or likened to an on-board crew. If it is assumed that the remote operator of an uncrewed vessel is able to take some action to assist, a state may argue that the remote operator is the ship’s master. In that case, it would be the responsibility of the remote operator to determine the level and type of assistance to offer in a particular circumstance. With the advances in the control and communication technology related to UxS, it is possible that this burden on a remote operator will be clarified in the legal realm in the near future.

The type of assistance owed is characterized in international law by its flexibility. Circumstances that may affect the assistance owed includes environmental and weather conditions and safety of the crews of both vessels. Mandrioli notes that, even if UxS “are technically limited in providing full assistance, flag States are still complying with the international duty” if they are offering the “maximum level of assistance achievable in the light of the existing circumstances.”[49]

This position is supported by the United Kingdom’s maritime policy. The Maritime Autonomous Surface Ships (MASS) UK Industry Conduct Principles and Code of Practice states that operators of UxS shall “make best endeavours to inform the appropriate search and rescue authorities.”[50] An opposing interpretation also relies on the flexible nature of the duty to assist. Because international law makes clear that the duty to assist is flexible and dependent upon circumstances, other states argue that UxS would be considered unable to assist people at sea due to their nature of being uncrewed.[51]

This analysis aligns with current technology, as most UxS have some level of remote operability. When UxS reach a level of true autonomy, these questions will become more complex. Will the design of an autonomous maritime system always require the ability to retake control of the system? Will technology or international law advance to find a balance between full autonomy and the duty to assist at sea? Will it ever be unlawful to produce uncrewed ships that are unable to rescue people at sea? While policies evolve and technology advances, these questions remain open.

Sea Lanes and Communications

From the above discussion, it is clear that UxS must comply with coastal state requirements just as a vessel would, including requirements for passage through designated sea lanes and communications with shore facilities.

UNCLOS Article 17 states that “ships of all states, whether coastal or land-locked, enjoy the right of innocent passage through the territorial sea.”[52] Article 19 defines the right of innocent passage, specifying limitations on certain activities.[53] If a state sets restrictions, they must be reasonable and necessary, not deny or impair the right of innocent passage, and not discriminate against the ships of any state.[54] If UxS are designated as ships, they retain the right of innocent passage and freedom from discrimination under UNCLOS, as long as they comply with the treaty and any state restrictions. In addition, if an uncrewed vessel is a vessel with sovereign immunity, it is not required to abide by designated sea lanes and traffic separation schemes but may do so voluntarily where practicable and compatible with the military mission and navigational safety dictates.[55]

In addition, US policy is that “properly flagged UxS enjoy the right of innocent passage in the territorial sea and archipelagic waters of other States, transit passage in international straits, and archipelagic sea lanes passage in archipelagic sea lanes.”[56] UxS that are not flagged as US ships may still be “deployed by larger vessels engaged in innocent passage, transit passage, or archipelagic sea lanes passage as long as their employment complies with the navigational regime of innocent passage, transit passage, or archipelagic sea lanes passage.”[57]

In addition, UxS can help crewed vessels to meet transit and communications requirements; for example, the US Coast Guard is currently using cutters and a growing network of uncrewed systems to detect and respond in the maritime environment.[58]

In terms of maritime domain awareness, UxS would benefit from having technology similar to that of crewed vessels and, at least in remotely controlled or semi-autonomous systems, a human-in-the-loop. UxS pose challenges when communications are lost or the system fails in some way and the craft becomes a navigational hazard, but likely no more so than a crewed vessel suffering the same failures. While technology is advancing, the law cannot keep pace; therefore, in the case of communications or navigation failures, international maritime law would apply to the UxS in the same way it would apply to a crewed vessel.

Sovereign Immunity of UxS

US Navy policy states that under customary international law, both “manned and unmanned vessels and aircraft owned or operated by a State, and used, for the time being, only for government non-commercial service are entitled to sovereign immunity.”[59] This position is affirmed in The Commander’s Handbook on the Law of Naval Operations, which states:

In all cases, U.S. Navy [UxS] are the sovereign property of the United States and immune from foreign jurisdiction. When flagged as a ship, [a UxS] may exercise the navigational rights and freedoms and other internationally lawful uses of the seas related to those freedoms. Unmanned systems may be designated as [a United States Ship] if they are under the command of a commissioned officer and manned by a crew under regular armed forces discipline, by remote or other means.[60]

This position was also affirmed by the State Department in a statement following the 2016 seizure of a US Navy uncrewed underwater vehicle (UUV) by China. The statement referred to the UUV as “a sovereign immune vessel of the United States” and called on China “to return our UUV immediately, and to comply with all of [China’s] obligations under international law.”[61]

This US position is consistent with UNCLOS’s interpretation and customary international law. As long as UxS qualify as ships and are operated by governments for exclusively non-commercial purposes, they will enjoy effectively the same sovereign immunity under UNCLOS that warships enjoy. Accordingly, UxS are immune from arrest, search, and inspection by foreign authorities; exempt from certain foreign taxes, duties, or fees; and officers, commanders, and masters (and, arguably, remote operators) retain the right to protect property aboard these vessels.

UxS and ISR

Maritime UxS have so proven their worth in the area of ISR that many are designed specifically for this purpose.

UxS may be used to exercise any internationally lawful use of the seas including intelligence, surveillance, and reconnaissance (ISR).[62] Maritime UxS have so proven their worth in the area of ISR that many are designed specifically for this purpose.[63] These technologies also are used in the area of port surveillance and security and offshore research applications.

Current research is also focused on enhancing autonomy and team/swarm mission capabilities by improving interoperability among UxS and supporting communication networks among UxS and crewed vessels, which is often a challenge in the maritime environment.[64] Figure 1 shows a conceptual scenario of underwater surveillance based on UxS being part of a team of vessels and other crafts. The scenario depicts a network of UxS with different missions, but within the same communications network and connected digitally to a support ship. The systems in these communication networks can be from one state or multiple states.

Figure 1. Conceptual scenario of underwater surveillance using UxS.[65]

It is well-settled law that intrusive ISR is legal in certain maritime zones but not in others. Specifically, ISR within a coastal state’s internal waters would be treated the same as intelligence collection is treated on land: within a coastal state’s territorial sea, intelligence collection by transiting ships would be considered inconsistent with that maritime zone’s innocent passage regime and, thus, illegal. However, beyond the territorial sea, ISR “is considered an internationally lawful use of the sea that is not subject to coastal State jurisdiction or interference.”[66]

Two significant challenges to the right to ISR beyond the territorial sea have arisen. Some states, notably China, claim that intrusive ISR is “inconsistent with the ‘peaceful purposes’ provisions of UNCLOS,” which generally prohibit ships in innocent passage from engaging in armed aggression.[67] However, state practice and Security Council deliberations affirm that the peaceful purposes clauses “do not prohibit all military activities on the high seas and in EEZs, but only those that threaten or use force in a manner inconsistent with the UN Charter.”[68] In the 1960s, the Soviet Union challenged the United States’ right to ISR in air and by sea by asking the UN Security Council to designate a US surveillance flight as an act of aggression; the effort failed by a vote of 9 to 2.[69]

While there likely will continue to be challenges to the use of UxS for ISR, it appears that, as long as the sole purpose of the UxS is ISR and not aggressive actions, international law allows for the design and operation of UxS for these purposes.

 

Recommendations

The authors recommend the following considerations for the US Navy as it moves forward with use of UxS as part of the force structure.

Recommendation 1. Solidify the assertion that UxS are considered vessels under UNCLOS and customary international law. To the extent that coastal states do not recognize UxS as vessels under international law, the UxS no longer benefit from navigation and other rights in the maritime environment. How a state defines UxS—as a vessel or not—can affect what level of due regard is owed to UxS as well as whether a state can assert sovereign immunity over such a system.

Recommendation 2. Integrate legal and policy considerations into the design and operation of UxS. Consideration of how a system may be treated under international law will yield a better-designed system that can more easily withstand legal challenges. Operators who understand what is well-settled under international law and what is not may be able to respond to circumstances in ways that would withstand legal scrutiny and better protect their state’s use of the systems.

Recommendation 3. Strengthen ally and partner collaboration on UxS design, use, and policy. Given the increase in use of UxS and their interactions with other vessels, the United States should prioritize collaboration with allies on the design and operation of UxS and the development of policies that can contribute to the establishment of customary international law or UxS-specific conventions in the future. By including policy considerations alongside technological advancements, the United States and its allies can mitigate the discrepencies between rapidly changing technology and slow-to-adapt laws.

The ambiguity surrounding the status of UxS can be taken advantage of to commit legally questionable actions.

Recommendation 4. Conduct additional research on how non-FVEY countries, especially US adversaries, define UxS. The ambiguity surrounding the status of UxS can be taken advantage of to commit legally questionable actions. Without the protections given to crewed vessels and ships under UNCLOS provisions, UxS are subject to legal uncertainty and possible unfair treatment by hostile nations. Two countries (China and Iran) have seized UxS belonging to the United States, and claimed their actions were legal and justified. If these nations, and other adversaries, do not consider UxS to be ships or vessels, they can make the case that UNCLOS does not apply. If states that seized the UxS do recognize the crafts as vessels, then their actions can be considered illegal seizures.

A better understanding of these issues can help to establish US and allies’ policies and enable leaders and operators to make legally informed decisions in-theater, while also contributing to effectively designed UxS in the future.

_______________________

About the Authors

Kristen Fletcher is Faculty Associate-Research in the Energy Academic Group at the US Naval Postgraduate School (NPS).

Marina Lesse is Faculty Associate-Research in the Energy Academic Group at the US Naval Postgraduate School.

Theresa Milio is a submarine officer serving in the US Navy.

This is a work of the US federal government and is not subject to copyright protection in the United States. Foreign copyrights may apply.

Image Credits

1. Photo by: NPS
2. Photo by: U.S. Navy photo by Mass Communication Specialist 2nd Class Jesse Monford, Public domain, via Wikimedia Commons

Endnotes