The Sinking of the Iranian Frigate Dena: Submarine Warfare and the Duty to Rescue Under the Geneva Conventions

The sinking of the Iranian naval frigate Dena off the southern coast of Sri Lanka has raised a narrow but important legal question under the law of armed conflict at sea: when a submarine destroys an enemy warship in waters where no hostile forces are present, does Article 18 of the Second Geneva Convention require that the attacking vessel attempt to rescue survivors?

Introduction

The destruction of the Iranian naval frigate Dena in March 2026 in the Indian Ocean off the southern coast of Sri Lanka has prompted legal scrutiny of the humanitarian obligations imposed by international law following naval engagements.

Article 18 of the Second Geneva Convention requires parties to a conflict to search for and collect shipwrecked personnel after engagements at sea. The rule appears straightforward. Yet the realities of modern naval warfare, particularly submarine warfare, complicate the application of this humanitarian duty.

The legal question is therefore not whether a duty exists, but whether the circumstances of the engagement made rescue operations feasible. In international humanitarian law, feasibility is often the decisive factor in determining whether a commander was required to undertake rescue measures following an attack.

Factual Background

The Iranian frigate Dena sank in the Indian Ocean several dozen nautical miles south of Sri Lanka within Sri Lanka’s maritime search and rescue region. The vessel was struck by a torpedo fired by a nuclear powered United States attack submarine.

The engagement occurred in waters off Sri Lanka where no hostile forces were present. The principal theatre of hostilities between Iran and Western forces lay thousands of miles away around the waters and airspace of Iran and the Persian Gulf.

Following the sinking of the vessel, Sri Lankan naval authorities conducted search and rescue operations and recovered survivors and bodies from the sea.

The legal issue arising from the incident therefore concerns the obligations of the attacking submarine in circumstances where the engagement occurred in waters far removed from the active theatre of war.

Applicable Law

The principal treaty governing humanitarian obligations during naval warfare is the Second Geneva Convention of 1949.

The crucial words within the provision are “all possible measures” and “whenever circumstances permit.” The obligation is therefore conditional rather than absolute. Commanders must undertake rescue operations only where doing so is operationally feasible.

This same principle appears within customary international humanitarian law.

Submarine Warfare and Operational Reality

Submarines occupy a distinctive position within naval warfare. Unlike surface vessels, submarines rely almost entirely upon stealth and concealment for their survival. When a submarine surfaces it becomes vulnerable to detection by aircraft, radar and anti submarine vessels.

Submarines also possess extremely limited deck space and cannot accommodate large numbers of survivors without compromising their ability to submerge.

For these reasons naval practice since the Second World War has generally treated the rescue obligation for submarines as conditional rather than absolute.

Where surfacing would expose the submarine to immediate military danger, the obligation to rescue survivors may be considered impracticable.

Historical Precedent

The tension between humanitarian law and submarine warfare first became apparent during the Second World War. After sinking the British troopship RMS Laconia in 1942, a German submarine surfaced and began rescuing survivors. While conducting rescue operations the submarine was attacked by an American aircraft.

The episode led German naval commander Karl Donitz to prohibit further rescue operations by submarines.

Following the war the legality of submarine warfare practices was examined at the Nuremberg proceedings. Evidence submitted during the trials indicated that American submarines had followed similar operational practices during the Pacific war.

The tribunal did not treat the failure of submarines to rescue survivors as a prosecutable war crime under those circumstances.

Jurisdictional Context

The sinking occurred outside Sri Lanka’s territorial waters but within its Exclusive Economic Zone and maritime rescue region.

Under the United Nations Convention on the Law of the Sea, coastal states exercise resource rights within the Exclusive Economic Zone but do not possess full sovereign jurisdiction over military operations conducted by foreign states in those waters.

Sri Lanka’s legal role therefore concerned the conduct of maritime search and rescue operations rather than the legality of the naval engagement itself.

Legal Assessment

Three observations arise from the circumstances of the incident.

First, an Iranian naval frigate engaged in hostilities constitutes a lawful military objective under the law of naval warfare.

Second, the duty imposed by Article 18 of the Second Geneva Convention is conditional rather than absolute. Commanders are required to undertake rescue operations only where operational circumstances permit.

Third, the particular circumstances of this engagement raise the question of feasible rescue. The attacking vessel was a nuclear powered submarine operating in waters where no hostile forces were present and far removed from the principal theatre of hostilities around Iran.

In international humanitarian law the concept frequently applied in such circumstances is that of feasible rescue. Commanders must take all measures that are practicable under the conditions prevailing at the time of the engagement.

Where operational risk is minimal, the scope of what constitutes feasible rescue may correspondingly expand. In such circumstances a tribunal examining the incident could ask whether reasonable rescue measures were available to the attacking submarine following the torpedo strike.

Conclusion

The sinking of the Iranian frigate Dena off Sri Lanka highlights a long standing tension within the law of armed conflict at sea. Humanitarian rules developed during an era dominated by surface fleets continue to govern modern naval warfare conducted by stealth platforms.

Article 18 of the Second Geneva Convention imposes a humanitarian obligation that is expressly conditioned by operational feasibility.

Where a submarine operates in contested waters, the obligation to rescue survivors may be limited by the need to preserve the safety of the vessel and its crew.

Where, however, the engagement occurs in uncontested waters far removed from the active theatre of conflict, the feasibility of rescue becomes a more demanding legal question.

Ultimately the legal issue raised by the sinking of Dena is therefore not whether the submarine was entitled to attack the vessel. Rather it is whether, once the engagement had concluded, the circumstances permitted humanitarian measures that international law requires belligerents to take whenever feasible.