Was the United States Legally Justified in Sinking an Iranian Warship?

A Doctrinal Analysis Under the Law of Naval Warfare and International Humanitarian Law

Abstract

Naval warfare remains a central component of interstate conflict, yet it operates within a highly structured legal regime derived from the United Nations Charter, customary international law, and humanitarian law governing armed conflict at sea. The reported sinking of an Iranian naval frigate by a United States submarine—resulting in significant loss of life—has intensified debates concerning the legality of maritime hostilities and the scope of lawful military targeting at sea.

This article evaluates whether such an action can be legally justified under contemporary international law. Drawing upon treaty frameworks, the law of naval warfare, the San Remo Manual on International Law Applicable to Armed Conflicts at Sea, and jurisprudence of international courts, the article assesses the legality of attacks against enemy warships and the humanitarian obligations that follow such engagements.

It argues that while warships are generally lawful targets during armed conflict, the legal justification ultimately depends upon the existence of an armed conflict, compliance with the principles of necessity and proportionality, and adherence to humanitarian obligations toward shipwrecked personnel.

1. Introduction

Maritime conflict has historically played a decisive role in shaping international law. From the naval blockades of the Napoleonic Wars to the submarine warfare campaigns of the twentieth century, naval operations have consistently raised complex legal questions regarding the permissible use of force at sea.

The recent sinking of an Iranian naval frigate by a United States submarine has revived these longstanding legal debates. The attack reportedly resulted in the deaths of more than eighty sailors and has significantly widened the geographic scope of the ongoing confrontation between the United States, Israel, and Iran.

Beyond its geopolitical implications, the incident raises critical legal questions:

• Under what circumstances can a state lawfully attack a warship belonging to another state?
• What legal regime governs such actions?
• What humanitarian obligations arise once a naval vessel has been disabled or destroyed?

Modern international law addresses these questions through a layered legal framework combining jus ad bellum, which regulates the legality of the use of force between states, and jus in bello, which governs the conduct of hostilities once an armed conflict exists.

The interaction between these two regimes is particularly complex in the maritime domain, where military vessels operate across international waters that remain open to all states.

This article examines the legality of the sinking of an Iranian warship by analyzing the relevant international legal framework, including the United Nations Charter, the law of naval warfare, and international humanitarian law. It also evaluates historical precedents and judicial interpretations that illuminate how international law approaches maritime military engagements.

2. The Legal Architecture Governing Maritime Conflict

Naval warfare is regulated by a sophisticated network of legal instruments that has evolved over more than a century. Unlike land warfare, where the Geneva Conventions provide detailed regulations, the law of naval warfare relies on a mixture of treaties, customary law, and authoritative military manuals.

Three primary legal regimes govern maritime hostilities:

• The law governing the use of force between states (jus ad bellum)
• International humanitarian law governing the conduct of hostilities (jus in bello)
• The law of the sea governing maritime jurisdiction

These frameworks operate simultaneously and must be interpreted together when evaluating the legality of naval engagements.

3. Jus Ad Bellum: The United Nations Charter and the Use of Force

The modern legal order governing interstate force is founded upon the prohibition established in Article 2(4) of the United Nations Charter, which requires states to refrain from the threat or use of force against the territorial integrity or political independence of another state.

This rule constitutes one of the most fundamental principles of contemporary international law. However, the Charter also recognizes two limited exceptions.

3.1 Self-Defence Under Article 51

Article 51 of the Charter preserves the inherent right of states to engage in individual or collective self-defence if an armed attack occurs.

The International Court of Justice clarified the scope of this right in the landmark case Nicaragua v United States (1986). The Court held that the exercise of self-defence must satisfy two essential conditions:

• Necessity
• Proportionality

These requirements are derived from customary international law and impose strict limitations on the use of defensive force.

In the context of naval warfare, a state may lawfully attack an enemy warship if the attack forms part of an ongoing armed conflict or if it constitutes a necessary act of self-defence against an imminent threat.

3.2 Security Council Authorization

The second exception to the prohibition on the use of force arises when the United Nations Security Council authorizes military action under Chapter VII of the Charter.

In the present case, there is no indication that the Security Council authorized the use of force against Iranian naval assets. Accordingly, any legal justification would need to rely upon the doctrine of self-defence or the existence of an armed conflict between the parties.

4. The Law of Armed Conflict at Sea

Once an armed conflict exists between states, the legality of military operations is governed primarily by international humanitarian law.

The law of armed conflict at sea is derived from several key treaties, including:

• The Hague Convention IX of 1907 concerning bombardment by naval forces
• The Hague Convention XIII of 1907 concerning the rights and duties of neutral powers in naval war
• The Second Geneva Convention of 1949 concerning wounded, sick, and shipwrecked members of armed forces at sea
• Additional Protocol I of 1977 concerning the protection of victims of international armed conflicts

Together, these instruments establish the fundamental humanitarian principles governing naval warfare.

5. Core Principles of International Humanitarian Law

International humanitarian law imposes several essential principles that regulate the conduct of hostilities.

5.1 Distinction

The principle of distinction requires parties to a conflict to distinguish between military objectives and civilian objects.

Warships, submarines, naval bases, and other military installations constitute legitimate military targets because they directly contribute to a state’s military operations.

Consequently, under the law of armed conflict, an enemy warship may generally be attacked without violating the principle of distinction.

5.2 Proportionality

The principle of proportionality prohibits attacks that would cause incidental civilian harm that is excessive in relation to the anticipated military advantage.

Although warships typically contain only military personnel, proportionality may still become relevant if an attack risks damage to nearby civilian vessels or infrastructure.

5.3 Military Necessity

Military necessity permits the use of force required to achieve a legitimate military objective, provided that the methods used are not otherwise prohibited by international law.

In naval warfare, military necessity often justifies attacks on enemy vessels capable of projecting military power.

6. The San Remo Manual and the Modern Law of Naval Warfare

One of the most influential contemporary sources on naval warfare is the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1994).

Although the Manual is not legally binding, it is widely regarded as an authoritative restatement of customary international law governing maritime hostilities.

The Manual was developed by a group of legal scholars and naval experts under the auspices of the International Institute of Humanitarian Law.

Several of its provisions are directly relevant to the legality of attacks on warships.

6.1 Lawful Targets

The San Remo Manual explicitly recognizes that enemy warships constitute lawful military objectives. These vessels may be attacked wherever they are encountered, provided they are located outside neutral territorial waters.

This rule reflects a long-standing principle of naval warfare that military vessels represent instruments of state power and therefore may be targeted during armed conflict.

6.2 Protection of Neutral States

The Manual also emphasizes the protection of neutral states and their territorial waters.

• Hostilities must not take place within the territorial sea of a neutral state unless that state itself becomes a party to the conflict.
• Attacks occurring in international waters, however, are generally permissible under the law of armed conflict.

7. The Protection of Shipwrecked Sailors

Even when an attack on a warship is lawful, international humanitarian law imposes important humanitarian obligations after the engagement.

The Second Geneva Convention of 1949 provides that wounded, sick, and shipwrecked members of armed forces at sea must be respected and protected.

Article 12 of the Convention requires parties to the conflict to take all possible measures to search for and collect shipwrecked personnel following naval engagements.

This obligation reflects the long-standing humanitarian tradition of assisting sailors in distress, regardless of nationality.

Failure to provide assistance where feasible may constitute a violation of international humanitarian law.

Key Humanitarian Obligations at Sea

• Respect and protection of wounded, sick, and shipwrecked sailors.
• Duty to search for and rescue survivors after naval engagements.
• Non-discriminatory humanitarian assistance regardless of nationality.
• Compliance with the Second Geneva Convention of 1949.

8. Maritime Zones and Jurisdiction

The legality of naval engagements also depends on the location of the attack.

Under the United Nations Convention on the Law of the Sea (UNCLOS), maritime space is divided into several zones.

Territorial Sea

States exercise sovereignty over their territorial sea, which extends up to twelve nautical miles from the coastline. Hostilities conducted within the territorial sea of a neutral state would violate international law.

Exclusive Economic Zone

The exclusive economic zone extends up to two hundred nautical miles from the coastline. Although coastal states enjoy certain economic rights in this zone, it remains open to navigation by foreign military vessels.

High Seas

The high seas are open to all states and represent the traditional domain of naval warfare.

If a naval engagement occurs on the high seas, it is generally governed solely by the law of armed conflict.

Summary of Maritime Zones

9. Historical Precedents

Historical incidents provide valuable insight into how international law has been interpreted in similar situations.

The Sinking of ARA General Belgrano (1982)

During the Falklands War, a British submarine torpedoed the Argentine cruiser ARA General Belgrano, resulting in the deaths of more than three hundred sailors.

The attack generated considerable controversy because the vessel was located outside the British-declared maritime exclusion zone.

Nevertheless, many legal scholars concluded that the attack was lawful because enemy warships remain legitimate targets regardless of exclusion zones.

Operation Praying Mantis (1988)

In 1988 the United States launched Operation Praying Mantis against Iranian naval forces in the Persian Gulf after Iranian mines damaged a U.S. naval vessel.

The operation resulted in the destruction of several Iranian ships and offshore installations.

Iran later brought a case before the International Court of Justice in Oil Platforms (Iran v United States) (2003). Although the Court did not rule directly on the legality of naval engagements, it reiterated that self-defence must satisfy the requirements of necessity and proportionality.

10. Judicial Interpretation of Wartime Conduct

International courts rarely adjudicate naval warfare directly, but several cases illuminate how courts interpret the laws of war.

In Ryuichi Shimoda v The State (1963), the Tokyo District Court examined the legality of wartime bombing and referenced Hague Convention rules governing naval bombardment.

The case demonstrates that courts may rely upon historical treaties and customary law when evaluating the legality of military actions.

Similarly, the jurisprudence of the International Court of Justice consistently emphasizes the centrality of necessity and proportionality in the use of force.

11. Legal Assessment of the Incident

Applying the above legal principles, the legality of the sinking of an Iranian warship depends upon several factors.

Existence of Armed Conflict

International humanitarian law applies once hostilities between states reach the threshold of international armed conflict. If the United States and Iran were already engaged in armed hostilities, the law of armed conflict would govern the attack.

Status of the Vessel

A commissioned naval warship constitutes a legitimate military objective under the law of armed conflict at sea. Consequently, its destruction would generally be lawful.

Compliance with Humanitarian Obligations

Even if the attack itself were lawful, the attacking state must still comply with humanitarian obligations toward survivors.

12. Political Legitimacy versus Legal Permissibility

International law distinguishes between legality and political legitimacy. An action may technically comply with the rules of international humanitarian law while still generating political controversy or diplomatic consequences.

Naval warfare in particular often occurs in politically sensitive regions where the risk of escalation is significant. Consequently, the legality of an attack does not necessarily determine whether the action will be viewed as legitimate by the international community.

13. Conclusion

The sinking of an Iranian warship by a United States submarine raises complex legal questions at the intersection of the law governing the use of force and the law regulating the conduct of hostilities.

Under the traditional law of naval warfare, enemy warships are legitimate military targets during armed conflict. The San Remo Manual and customary international law both recognize this principle.

However, the legality of the attack ultimately depends upon whether the conditions for the lawful use of force were satisfied. If the attack formed part of an ongoing armed conflict or constituted a necessary act of self-defence, it may fall within the framework of lawful military operations.

At the same time, international humanitarian law imposes continuing obligations toward shipwrecked sailors and requires that parties to a conflict minimize unnecessary suffering.

The incident therefore illustrates the continuing tension between military necessity and humanitarian restraint in modern maritime conflict. As naval technology evolves and geopolitical rivalries intensify, the law of armed conflict at sea will remain a critical component of the international legal order.

References

Treaties and Legal Instruments

• United Nations Charter (1945)
• Hague Convention IX (1907)
• Hague Convention XIII (1907)
• Geneva Convention II (1949)
• Additional Protocol I to the Geneva Conventions (1977)
• United Nations Convention on the Law of the Sea (1982)
• San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1994)

Cases

Books

• Yoram Dinstein, The Conduct of Hostilities under the Law of International Armed Conflict
• Wolff Heintschel von Heinegg, The Law of Naval Warfare
• J. Ashley Roach, Naval Warfare and the Law of the Sea

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