U.S. Strikes Iranian Oil Tankers: Military Objectives and Economic Warfare Under IHL

Introduction

On September 5, 2026, the United States struck three Iranian oil tankers after the Islamic Revolutionary Guard Corps launched ballistic missiles toward two U.S. Navy warships. U.S. Central Command identified the vessels as Downy, Stark 1, and Kylo/Noxen and alleged that they formed part of a multibillion-dollar network financing the IRGC and its regional proxies. CENTCOM also presented the operation in explicitly economic terms: the response to attacks on two American ships would impose a greater “economic cost” by striking three Iranian vessels (U.S. Central Command, 2026). The US strikes on Iranian oil tankers consequently raise a question extending beyond the immediate military exchange: when can a commercial vessel that generates or transports revenue for an armed force become a lawful military objective?

International humanitarian law does not make civilian property targetable merely because destroying it would harm the enemy. Article 52(2) of Additional Protocol I defines military objectives as objects which, by their nature, location, purpose, or use, make an effective contribution to military action and whose destruction, capture, or neutralization offers a definite military advantage in the circumstances ruling at the time (Additional Protocol I, 1977, art. 52(2)). Neither the United States nor Iran is a party to Additional Protocol I, although both signed it in 1977. The core definition of military objectives is nonetheless widely recognized as reflecting customary international humanitarian law (ICRC, 2005, Rule 8).

The difficult issue is the required connection between economic activity and military action. A commercial tanker carrying fuel directly for military operations presents a different case from one whose alleged contribution consists of generating oil revenue that eventually supports military expenditure. Melzer’s account of the targeting rule distinguishes an effective contribution to military action from support for mere policy objectives or the enemy’s general war-sustaining capabilities (Melzer, 2019, p. 92). Under that approach, the economic importance of an object cannot, without more, remove its civilian protection.

U.S. doctrine adopts a broader interpretation. The Department of Defense understands “military action” to include the general prosecution of war and recognizes objects contributing effectively to an adversary’s war-fighting or war-sustaining capability as potential military objectives. Its approach can encompass certain economic objects where their function materially sustains the enemy’s ability to conduct hostilities (U.S. Department of Defense, 2023). This position is significant to the September 5 attacks, but it should not be treated as an uncontested statement of customary international law. The dispute concerns how close the relationship must be between an economic asset and actual military action before the protection ordinarily afforded to civilian objects is lost.

CENTCOM’s emphasis on economic cost also engages the second element of the military-objective definition. Economic damage may produce military effects, but economic loss is not synonymous with the definite military advantage required by IHL. The legality of attacking each tanker depends both on the contribution attributed to that particular vessel and on the military advantage reasonably anticipated from its destruction or neutralization. An asserted connection to IRGC financing may be relevant evidence, but it does not itself resolve either element of the test.

These targeting questions remain distinct from the broader law governing the resort to force. A state acting in self-defense under the jus ad bellum must still comply with the rules governing the conduct of hostilities. Retaliatory language likewise does not automatically establish a belligerent reprisal, which has a separate and restrictive legal character. The central legal issue raised by the tanker strikes is narrower and more demanding: whether the relationship between each commercial vessel and IRGC financing was sufficient to make it a military objective, and whether attacking it offered the definite military advantage required by international humanitarian law.

1. US Strikes Iranian Oil Tankers on September 5

U.S. Central Command reported that American forces struck three crude-oil tankers on September 5, 2026, after the Islamic Revolutionary Guard Corps launched ballistic missiles toward two U.S. Navy warships patrolling regional waters. According to CENTCOM, an aircraft carrier and a guided-missile destroyer evaded multiple Iranian attacks, and no American personnel were harmed (U.S. Central Command, 2026).

The American response involved three vessels in separate locations. CENTCOM stated that Downy was permanently disabled off the coast of Kharg Island and Stark 1 was permanently disabled near Jask. The third vessel, Kylo, which CENTCOM identified as also known as Noxen, was unladen in the Gulf of Oman. Its crew was directed to abandon ship before U.S. forces struck several critical locations and, according to CENTCOM, completely destroyed the tanker (U.S. Central Command, 2026).

Official U.S. sanctions records add important details about the vessels without resolving their status under the law of armed conflict. OFAC lists Downy as an Iran-flagged crude-oil tanker linked to the National Iranian Tanker Company and identifies it by IMO number 9218480. Stark 1, listed by OFAC as STARK I, IMO 9171450, is likewise Iran-flagged and linked to the National Iranian Tanker Company (OFAC, 2026a; OFAC, 2026b). Kylo, IMO 9189146, is listed as Comoros-flagged and linked to Kylo Shipping Inc. OFAC records Memphis as an alias for that vessel, whereas CENTCOM described Kylo as also known as Noxen (OFAC, 2026c).

CENTCOM further alleged that the three tankers formed part of a multibillion-dollar shadow network funding the IRGC and its regional proxies. That allegation is legally significant because the asserted financial relationship lies at the center of the targeting justification. It does not, however, establish by itself that any of the vessels qualified as a military objective. Sanctions designation, enemy ownership or control, participation in Iranian oil exports, and lawful targetability are distinct legal questions.

The stated purpose of the operation makes the distinction especially important. CENTCOM commander Admiral Brad Cooper described the strikes as imposing a higher “economic cost” on Iran after missiles were fired toward two American warships (U.S. Central Command, 2026). The language raises a question that cannot be answered simply by identifying the tankers as Iranian economic assets: international humanitarian law requires a legally sufficient relationship to military action and a definite military advantage from attacking the particular object.

2. Enemy Merchant Vessels in Naval Warfare

Naval warfare distinguishes enemy warships from enemy merchant shipping. Enemy warships and military aircraft are generally military objectives by their nature, subject to the specific exemptions from attack recognized by the law of naval warfare. Enemy merchant vessels occupy a different position. Their enemy character does not, without more, make them liable to direct attack.

The San Remo Manual on International Law Applicable to Armed Conflicts at Sea provides an influential modern statement of these rules. Prepared by international lawyers and naval experts convened by the International Institute of Humanitarian Law and finalized in 1994, the Manual is a non-binding expert restatement rather than a treaty. Its provisions remain significant because they synthesize established rules and identify areas in which naval warfare requires more specialized treatment than general land-warfare formulations.

Paragraph 59 provides that enemy merchant vessels may be attacked only if they meet the definition of a military objective. Paragraph 60 identifies conduct capable of producing that result, including engaging in belligerent acts, acting as an auxiliary to enemy armed forces, transporting troops, replenishing warships, participating in intelligence activity, resisting visit or search, and otherwise making an effective contribution to military action, such as by carrying military matériel (San Remo Manual, 1994, paras. 59–60). By contrast, enemy warships, military aircraft, and auxiliary vessels are military objectives unless protected by one of the Manual’s specific exemptions from attack (para. 65).

Enemy character is a related but separate inquiry. Under the San Remo framework, an enemy flag constitutes conclusive evidence of enemy character, whereas a neutral flag is prima facie evidence of neutral character. Registration, ownership, charter, control, and other criteria may also be relevant (San Remo Manual, 1994, paras. 112–117). A finding of enemy character can affect rights of interception and capture without automatically satisfying the additional conditions required for direct attack on a merchant vessel.

That distinction is particularly relevant to Kylo. OFAC lists the tanker as Comoros-flagged, so its enemy character cannot simply be inferred from CENTCOM’s collective description of the three ships as Iranian crude-oil carriers. A neutral flag is not conclusive: the law of naval warfare allows enemy character to be established through other evidence and provides mechanisms such as visit, search, and capture where appropriate. Neutral merchant vessels may also become liable to attack in specified circumstances, but the conditions are more restrictive than those governing enemy warships (San Remo Manual, 1994, paras. 67–68, 112–117).

The nature of a tanker’s activity can consequently be decisive. A merchant vessel delivering fuel directly to warships, carrying military matériel, or functioning as an auxiliary presents a conventional military-support case. An oil tanker carrying crude for commercial export, whose alleged military contribution consists instead of generating revenue for the belligerent or its armed forces, raises the more contested question of economic or war-sustaining targets.

3. The Military-Objective Test

For attacks against vessels at sea, the military-objective rule is most securely stated as a rule of customary international humanitarian law and through the specialized naval formulation in paragraph 40 of the San Remo Manual. That provision limits military objectives to objects which, by their nature, location, purpose, or use, make an effective contribution to military action and whose destruction, capture, or neutralization offers a definite military advantage in the circumstances ruling at the time (San Remo Manual, 1994, para. 40).

The language substantially reproduces Article 52(2) of Additional Protocol I, but the treaty provision requires a jurisdictional qualification in a naval case. Article 49(3) provides that the relevant Section of Additional Protocol I applies to warfare affecting civilians or civilian objects on land and to attacks from the sea or air against objectives on land, while otherwise leaving the international rules governing armed conflict at sea unaffected (Additional Protocol I, 1977, art. 49(3)). Article 52(2) is thus significant here as the familiar treaty formulation of the test, not as a treaty provision directly regulating every sea-to-sea attack.

There is a further treaty-status limitation. The United States and Iran both signed Additional Protocol I in 1977, but neither has become a party to it (ICRC Treaty Database, 2026). Article 52(2) consequently cannot be applied to either state merely as a conventional obligation arising from treaty participation. The substantially corresponding two-part definition of military objectives is, however, widely regarded as customary international humanitarian law (ICRC, 2005, Rule 8).

Both elements of the definition are cumulative. The first asks whether the object, through its nature, location, purpose, or use, effectively contributes to military action. The second concerns the advantage expected from its destruction, capture, or neutralization. Economic importance, enemy ownership, or some relationship with the armed forces cannot substitute for either requirement. A military connection alone is insufficient if neutralizing the object offers no definite military advantage, just as economic damage to the enemy cannot independently establish an effective contribution to military action.

Classification also depends on the circumstances existing when the targeting decision is made. Merchant vessels can change cargo, charter arrangements, routes, customers, ownership structures, and functions. A tanker used on one voyage to supply armed forces may qualify as a military objective during that operation without acquiring permanent targetable status. Historical association or sanctions designation may provide relevant intelligence, but the legal inquiry remains directed to the contribution and anticipated advantage attributable to the particular vessel at the relevant time.

4. Financing the IRGC and Effective Contribution

Direct military logistics provide the clearest cases. A tanker delivering fuel earmarked for warships or combat aircraft, transporting military equipment, carrying troops, or otherwise serving the armed forces can make an effective contribution to military action through its use or purpose. The San Remo Manual’s treatment of merchant vessels reflects precisely this type of operational nexus (San Remo Manual, 1994, para. 60).

Revenue generation presents a more difficult problem. Commercial oil exports produce income that may eventually pay for weapons, military salaries, procurement networks, infrastructure, or support to allied armed groups. Yet the eventual use of money for military purposes does not by itself determine whether the vessel generating or transporting the commodity is sufficiently connected to “military action” within the meaning of the targeting rule.

Melzer’s account of the customary targeting framework adopts a restrictive understanding of that connection. It distinguishes an effective contribution to military action from support for policy objectives or the enemy’s general war-sustaining capabilities (Melzer, 2019, p. 92). On that interpretation, the economic importance of oil exports to a belligerent cannot transform every refinery, terminal, tanker, or commercial transaction associated with those exports into a military objective.

Ownership can strengthen the evidentiary case without replacing the legal test. Direct ownership or control by the IRGC could be highly relevant to enemy character and might also support conclusions about a tanker’s purpose, use, or status as an auxiliary. Ownership alone, however, does not establish that a merchant tanker makes an effective contribution to military action and that its neutralization offers a definite military advantage.

The nexus becomes materially stronger when a particular commercial transaction is integrated into military procurement. Revenue from an ordinary export entering general state accounts is more remote from hostilities than proceeds earmarked for weapons purchases or routed through a financial mechanism dedicated to military acquisition. A shipment conducted as part of an organized system exchanging petroleum revenue for armaments would provide stronger evidence of effective contribution than participation in the national oil economy alone.

Recent U.S. Treasury actions provide context for CENTCOM’s allegation. In April 2026, Treasury stated that Iranian shadow-banking networks allowed the IRGC and other armed forces to receive payments for oil sales, purchase components for missiles and other weapons systems, and transfer funds to Iranian-backed groups (U.S. Department of the Treasury, 2026a). In May, Treasury separately alleged that front companies facilitating IRGC oil sales to China were channeling revenue toward weapons development and proxy support (U.S. Department of the Treasury, 2026b). These are official U.S. government findings and allegations; they do not establish that every vessel participating in Iranian petroleum exports performs the same military-financing function.

CENTCOM’s September statement is more specific in one respect: it places Downy, Stark 1, and Kylo/Noxen within a network allegedly funding the IRGC and its proxies. What remains less clear from the public account is the precise role attributed to each tanker. A vessel transporting oil through a financing arrangement directly supporting procurement or operations presents a different legal case from one that merely increases Iran’s general export earnings.

The dispute consequently turns on the degree of integration rather than the economic value of petroleum in the abstract. If the voyages were organized to produce or transfer funds specifically sustaining IRGC military operations, the argument for effective contribution becomes appreciably stronger. If the connection consists only of generating commercial revenue available to the Iranian state or economy generally, the case is considerably weaker under the narrower interpretation of the military-objective rule.

5. The U.S. War-Sustaining Interpretation

U.S. doctrine takes a broader approach to effective contribution than the restrictive interpretation described above. The Department of Defense Law of War Manual explains that “military action” is not confined to a specific battle or operation and may encompass the general prosecution of war. On this view, an object may effectively contribute to an opposing force’s war-fighting or war-sustaining capability even when the contribution is not immediate or tied to a particular tactical operation (U.S. Department of Defense, 2023, § 5.6.6.2).

That approach extends to certain economic objects. The DoD Manual records that economic assets associated with military operations or with war-supporting or war-sustaining industries have been regarded as military objectives. Among its examples are oil refining and distribution facilities and objects associated with petroleum, oil, and lubricant production, transportation, storage, and distribution (U.S. Department of Defense, 2023, § 5.6.8.5). The formulation can encompass petroleum transportation assets, but it does not establish a rule that oil tankers are targetable as a class.

War-sustaining terminology also appears in U.S. federal legislation. Title 10 defines a “military objective,” for purposes of the military-commissions subchapter, to include objects that effectively contribute to an opposing force’s “war-fighting or war-sustaining capability,” provided their destruction, capture, or neutralization would constitute a definite military advantage under the circumstances at the time of attack (10 U.S.C. § 950p(a)(1)). Because the provision expressly defines terms for that statutory subchapter, it is better understood here as a domestic parallel demonstrating the incorporation of war-sustaining terminology into U.S. law, not as an independent source governing CENTCOM targeting decisions.

The American interpretation remains contested internationally. The 2025 second edition of the Newport Manual on the Law of Naval Warfare records divided state practice and reports that a majority of states do not regard a war-sustaining contribution, standing alone, as falling within the definition of military objectives (Newport Manual Expert Group, 2025). The ICRC approach similarly requires a closer relationship to military action than support for the adversary’s general war-sustaining capacity (Melzer, 2019).

This disagreement has direct consequences for Iranian petroleum exports. Under the U.S. interpretation, a tanker whose commercial activity materially produces funds sustaining IRGC war-fighting capacity may satisfy the effective-contribution requirement even if it is not carrying weapons, troops, or fuel directly to military units. Under the narrower approach, revenue production may remain too remote unless the vessel is more specifically integrated into military procurement, logistics, financing, or operations.

Even the broader U.S. position does not make CENTCOM’s description legally conclusive. The ordinary two-part test remains: the particular object must effectively contribute to military action as the United States understands that concept, and destroying, capturing, or neutralizing it must offer a definite military advantage in the circumstances ruling at the time. The central legal dispute is consequently not whether Iranian oil revenues can support the IRGC. It is whether the military-financing relationship attributed to each of these tankers was sufficiently concrete to cross the boundary between economic activity and a lawful military objective.

6. Economic Cost and Military Advantage

An effective contribution to military action is only the first part of the military-objective test. The second requires the destruction, capture, or neutralization of the object to offer a definite military advantage in the circumstances ruling at the time. Paragraph 40 of the San Remo Manual adopts this cumulative formulation for naval warfare. An object cannot qualify merely because it assists the enemy in some way; the anticipated consequence of attacking it must also be military in character (San Remo Manual, 1994, para. 40).

The required advantage need not be immediate or confined to a single tactical engagement. U.S. doctrine permits military advantage to be considered in relation to the broader operation or strategy and describes the required benefit as concrete and perceptible rather than hypothetical or speculative (U.S. Department of Defense, 2023). Disrupting an adversary’s ability to procure weapons, replenish forces, finance military operations, or maintain a military supply system may accordingly produce an advantage even when the effect develops over time.

CENTCOM’s statement that the tanker strikes were intended to impose a higher “economic cost” on Iran makes the distinction between economic loss and military advantage particularly important. Destruction of commercial property may reduce an enemy’s wealth without impairing its armed forces in any definite way. Financial damage becomes legally relevant to the second limb only insofar as it is reasonably expected to yield an identifiable military benefit rather than simply punish the adversary or diminish its general economic resources.

The strongest argument would link the loss of a particular tanker to a concrete disruption in IRGC military capacity. Preventing revenue from reaching a procurement mechanism, interrupting payment for weapons or missile components, disabling a vessel integral to military logistics, or degrading a financial network used to sustain ongoing operations could satisfy that requirement if the expected effect were sufficiently definite. The scale of the monetary loss alone would not establish the necessary advantage.

Force protection may also be relevant. Reducing an identified capability used to threaten U.S. forces can provide military advantage, including where the effect improves the security of those forces. Broader deterrence is harder to characterize. A reasonably anticipated operational reduction in future attacks is different from imposing punishment to demonstrate resolve or to create generalized political deterrence. The latter cannot simply be assumed to satisfy the military-advantage requirement because it may operate principally at the level of signaling rather than military capability.

CENTCOM has not publicly disclosed the targeting intelligence or operational assessments underlying its selection of Downy, Stark 1, and Kylo/Noxen. The public emphasis on economic cost does not establish that economic punishment was the only anticipated benefit, but undisclosed possibilities cannot resolve the legal question either. On the available record, legality under the second limb depends on whether the loss of each tanker was reasonably expected to weaken an identifiable element of Iran’s military capacity rather than merely inflict economic damage.

7. Retaliation and Belligerent Reprisals

The chronology of the September 5 operation makes retaliation an understandable political description. Iran launched missiles toward two U.S. warships, and American forces subsequently attacked three tankers. International law, however, assigns different consequences to self-defense, ordinary military retaliation, and belligerent reprisals. The sequence of attacks does not determine which legal category applies.

Article 51 of the UN Charter recognizes the inherent right of individual or collective self-defense if an armed attack occurs. That rule belongs to the jus ad bellum. International humanitarian law separately regulates the conduct of hostilities once an armed conflict exists. Even force used lawfully in self-defense remains subject to distinction, targeting, proportionality, and precautions, while an attack that violates the prohibition on the use of force is not automatically unlawful under every rule of IHL.

This separation is significant for the Iranian missile launches. Enemy warships are generally military objectives under naval warfare law, subject to the specific exemptions applicable to protected vessels (San Remo Manual, 1994, para. 65). If Iran directed its missiles at U.S. warships during an international armed conflict and otherwise complied with the rules governing attacks, the strike would not become an IHL violation merely because the United States regarded Iran’s resort to force as unlawful or unprovoked. A jus ad bellum violation and an IHL violation are analytically distinct.

Belligerent reprisals occupy a narrower category. In traditional law-of-war doctrine, a reprisal is conduct that would otherwise be unlawful but is undertaken in response to an adversary’s prior violation of IHL for the purpose of inducing future compliance. U.S. doctrine treats reprisals as exceptional, requiring consideration of the prior violation, attempts to secure compliance through other reasonably available means, proportionality, and appropriate authorization; authority to order them is generally retained at the national level (U.S. Department of Defense, 2023).

Additional Protocol I prohibits reprisals against civilian objects in Article 52(1), but its application to warfare at sea requires care. Article 49(3) limits the direct application of the relevant Section of the Protocol in naval warfare, principally preserving the pre-existing international rules applicable to armed conflict at sea except where attacks affect civilians or civilian objects on land. Neither the United States nor Iran is a party to the Protocol in any event. The customary position is also not entirely uniform: the ICRC records extensive state support for prohibiting reprisals against civilian objects but acknowledges contrary practice sufficient to leave the universal customary status of such a prohibition contested (ICRC, 2005, Rule 147).

That controversy does not provide an easy legal basis for the September 5 strikes. A belligerent reprisal still requires a prior violation of IHL. If the Iranian missiles were lawfully directed against U.S. warships under the conduct-of-hostilities rules, those attacks could not themselves supply the antecedent IHL breach necessary to justify an otherwise unlawful reprisal against civilian property.

CENTCOM did not publicly identify a prior law-of-war violation or characterize the tanker strikes as belligerent reprisals. Its explanation is more consistent with treating the vessels as military objectives and using retaliatory or deterrent language to explain the timing and scale of the response. That remains an inference from the public record rather than a formal statement of the legal theory relied upon by the United States.

8. Proportionality and Precautions at Sea

Military-objective status does not eliminate the remaining constraints on attack. Customary IHL requires feasible precautions to verify that intended targets are military objectives, to select means and methods that reduce incidental harm, and to cancel or suspend an attack where the legal conditions for proceeding are no longer satisfied. The San Remo Manual reflects corresponding precautionary rules for naval warfare (San Remo Manual, 1994, para. 46; ICRC, 2005, Rules 15–19).

Proportionality is a separate inquiry. An attack on a lawful military objective is prohibited where the expected incidental harm would be excessive in relation to the concrete and direct military advantage anticipated (ICRC, 2005, Rule 14). The classification of a tanker and the consequences of attacking it must consequently be analyzed independently: precautions cannot transform a civilian object into a military objective, while lawful targetability does not remove all restraints on the manner of attack.

The position of civilians aboard targetable vessels is more difficult in naval warfare than an ordinary land-targeting formulation suggests. Merchant mariners do not lose civilian status merely because the vessel on which they serve becomes a military objective. Yet naval warfare has traditionally taken a more platform-centered approach to persons embarked on military objectives, and contemporary expert analysis remains divided over precisely how civilian crew members aboard a targetable merchant vessel are to be treated in the proportionality calculation. Their personal civilian status and the legal consequences of their presence aboard the vessel are distinct questions.

Kylo presents an additional issue because OFAC identified it as Comoros-flagged. If it retained neutral merchant-vessel status under naval warfare law, paragraph 67 of the San Remo Manual becomes particularly relevant. Where a neutral merchant vessel otherwise makes an effective contribution to enemy military action, attack is subject to additional safeguards, including the requirement, where applicable, that it not be feasible first to place passengers and crew in a place of safety (San Remo Manual, 1994, para. 67). The Manual also contemplates warning in circumstances where warning is practicable.

CENTCOM reported that Kylo was unladen and that its crew was directed to abandon ship before U.S. forces attacked several critical locations (U.S. Central Command, 2026). If the vessel was legally neutral, rather than merely sailing under a neutral flag, that evacuation could be relevant not only as general evidence of precautions but also to the specialized naval rule protecting passengers and crew before attack. The public record does not establish enough about the circumstances to determine whether all elements of that rule were engaged or satisfied.

Comparable information has not been publicly disclosed for Downy and Stark 1. Their crew arrangements, cargo condition at the time of attack, surrounding traffic, and the precise means used against them are relevant to a complete precautionary assessment. The absence of public information does not imply that precautions were not taken; it limits the conclusions that can be drawn from open sources.

Environmental risks also form part of the legal analysis. Customary IHL requires methods and means of warfare to be employed with due regard for protection of the natural environment and requires feasible precautions against incidental environmental damage (ICRC, 2005, Rules 43–44). Foreseeable damage to the marine environment can itself be relevant to proportionality rather than only when environmental harm produces additional injury to civilians or civilian property.

CENTCOM’s statement that Kylo was unladen reduces one obvious concern but does not eliminate environmental risk. An empty crude carrier may still contain bunker fuel, residues, lubricants, or other hazardous substances. No comparable public information establishes the cargo status of the other two vessels. A legally sound assessment cannot infer either a major oil spill or the absence of environmental danger without evidence concerning the condition of each tanker when attacked.

9. What the Evidence Shows for Each Tanker

The legal position cannot be determined collectively merely because CENTCOM grouped all three vessels within the same alleged financing network. Public records establish significant differences in flag, corporate links, sanctions history, and known operational circumstances. Those differences affect enemy character and may also bear on the military-objective analysis.

Downy, IMO 9218480, appears in OFAC records as an Iran-flagged crude-oil tanker associated with the National Iranian Tanker Company. CENTCOM reported that American forces permanently disabled it off Kharg Island (OFAC, 2026a; U.S. Central Command, 2026). Under the San Remo Manual, an enemy flag constitutes conclusive evidence of enemy character. That resolves one classification question within the Manual’s framework, but it does not establish that an enemy merchant vessel may be attacked. The separate military-objective test still applies.

Stark 1, identified by OFAC as STARK I, IMO 9171450, has a similar profile. It is recorded as Iran-flagged and associated with NITC, while CENTCOM stated that it was permanently disabled near Jask (OFAC, 2026b; U.S. Central Command, 2026). Its enemy character is accordingly easier to establish than its targetability. Publicly disclosed official information does not demonstrate that it was carrying military supplies, functioning as an auxiliary, delivering fuel to armed forces, or otherwise performing one of the conventional military-support functions recognized in naval warfare law at the time of attack.

Kylo is more complicated. OFAC lists IMO 9189146 as a Comoros-flagged tanker connected to Kylo Shipping Inc. and sanctioned under Iran-related authorities. Treasury had previously linked the vessel and its associated company to the Mohammad Hossein Shamkhani shipping network, which U.S. authorities have described as facilitating large-scale Iranian petroleum exports and sanctions evasion (U.S. Department of the Treasury, 2025; OFAC, 2026c). CENTCOM referred to the vessel as Kylo/Noxen, whereas OFAC lists Memphis as an alias. The shared IMO number is the strongest basis for identifying the records as concerning the same ship.

A Comoros flag constitutes prima facie evidence of neutral character under the San Remo Manual, not conclusive proof. Registration, ownership, control, charter arrangements, and other evidence may rebut that presumption (San Remo Manual, 1994, paras. 112–117). If Kylo remained a neutral merchant vessel for the purposes of naval warfare law, the stricter conditions governing attacks on neutral merchant vessels would become relevant in addition to the ordinary military-objective test.

CENTCOM’s statement that Kylo was unladen also narrows the factual basis for treating its immediate cargo as a military contribution. Its legal status would instead have to depend on some other relevant feature of its nature, location, purpose, or use. Purpose may encompass an intended future use, but such an assessment requires reasonably grounded information about that intended employment; sanctions history or previous commercial activity does not automatically establish future military use.

Economic-sanctions law performs a different function from targeting law. OFAC designation can establish that the United States has blocked a vessel or associated entity under particular sanctions authorities and can provide evidence of relationships with sanctioned networks. It does not constitute a determination that the vessel is a military objective under IHL. Conversely, absence from a sanctions list would not prevent a merchant vessel from becoming a military objective through its actual use or purpose during hostilities.

The publicly disclosed evidence is consequently stronger on economic and institutional connections than on the elements needed for definitive IHL classification. Downy and Stark 1 are demonstrably linked to NITC and bear an Iranian flag; Kylo is documented within a U.S.-sanctioned Iranian petroleum-shipping network. CENTCOM alleged that all three belonged to a network funding the IRGC and its proxies. What has not been publicly disclosed is the ship-specific targeting intelligence showing how each vessel contributed to military action, what revenues or transactions were tied to military procurement or operations, and what definite military advantage was expected from neutralizing each tanker.

That evidentiary limit precludes a categorical conclusion based solely on publicly available information. It does not establish that CENTCOM lacked additional intelligence. It means only that the legality of each attack cannot be demonstrated from official labels, sanctions records, or the general economic importance of Iranian petroleum exports alone.

Also read

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Conclusion

The legality of attacking an oil tanker cannot be determined merely by showing that its trade benefits an adversary or that revenues ultimately support state military expenditure. Under the narrower approach to the military-objective definition, general economic or war-sustaining contribution is insufficient without a closer connection to military action. U.S. doctrine adopts a broader position, permitting certain objects that effectively sustain an adversary’s war-fighting capacity to qualify, but it still requires both an effective contribution and a definite military advantage.

The September 5 tanker strikes place that disagreement in a concrete naval setting. The 2025 Newport Manual records divided state practice on war-sustaining objects and identifies rejection of war-sustaining contribution alone as the majority position among states. The U.S. interpretation consequently provides a broader route to treating revenue-producing petroleum assets as military objectives than the approach reflected in the ICRC’s analysis and the position attributed to the majority of states.

CENTCOM’s emphasis on imposing a higher economic cost does not resolve the dispute. Economic degradation can produce a military advantage when it disrupts procurement, logistics, financing, or another identifiable military capability. Economic punishment, general revenue loss, and strategic signaling cannot simply be equated with the definite military advantage required by the targeting rule.

The public evidence establishes substantial connections between the vessels and Iranian petroleum networks but reveals considerably less about their individual military functions. If U.S. targeting intelligence showed that particular voyages, revenues, or transactions directly sustained IRGC procurement or operations, the argument for targetability would be materially stronger, especially under the American war-sustaining interpretation. No equivalent ship-specific evidentiary record has been publicly disclosed.

A definitive legal judgment on all three strikes would consequently go beyond the information currently available. Downy, Stark 1, and Kylo/Noxen must each be assessed according to their own enemy or neutral character, nature, location, purpose and use, the military advantage anticipated from their neutralization, and the precautions required in the circumstances. The September 5 operation demonstrates how sharply the law can turn on the boundary between weakening an enemy economically and attacking an object because of its effective contribution to military action.

References

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