The sinking of the Iranian frigate IRIS Dena by a United States Navy submarine on March 4, 2026, approximately 40 nautical miles off the coast of Sri Lanka, has raised questions about the legality of the action and the obligations surrounding the rescue of survivors. The incident, occurring amidst the broader 2026 Iran war, marks a significant escalation and highlights the complex legal framework governing naval warfare.
The attack, which resulted in the deaths of 87 sailors and the rescue of 32 others, according to Sri Lankan officials, underscores the rarely understood rules of engagement at sea. Was the sinking of the IRIS Dena permissible under international law? And what responsibilities did the US Navy have to those onboard?
Understanding the answers requires delving into the law of naval warfare, a subset of the broader law of armed conflict. This body of law establishes permissions and protections for combatants, civilians and neutral parties involved in maritime conflict. Critically, these rules apply regardless of the initial legal justification for resorting to force, meaning adherence to the law of the sea is expected even if the war itself is considered unlawful under international law.
The law of naval warfare governs operations at sea whether or not a formal declaration of war has been made, and it takes precedence over the United Nations Convention on the Law of the Sea when the two conflict, adhering to the principle of lex specialis – the more specific law applies. These regulations have evolved over centuries as nations sought to balance effective naval operations with humanitarian considerations.
Was the Attack on IRIS Dena Legal?
Under the law of naval warfare, warships of a state engaged in an international armed conflict are considered legitimate military objectives. The rules permit targeting such vessels on the high seas or within the 12 nautical mile territorial waters of states directly involved in the conflict. An attack outside the 12 nautical mile territorial waters of neutral states, like Sri Lanka, is generally considered lawful. Reports indicate the IRIS Dena was operating outside Sri Lankan territorial waters at the time of the attack, making it a lawful target, according to these standards.
A U.S. Submarine sank an Iranian warship in the Indian Ocean, as Washington and Israel intensified their bombardment Wednesday of Iran’s security forces and other symbols of power. (AP Photo)
Obligations Regarding Rescue of Survivors
The Second Geneva Convention of 1949 outlines obligations regarding the rescue of shipwrecked, wounded, and sick individuals following any engagement. These rules extend to naval warfare, requiring belligerents to assist survivors at sea “so far as military circumstances permit.” However, submarines face unique challenges in fulfilling this obligation. Surfacing to conduct a rescue operation can expose the submarine to significant risk, and the limited space onboard makes accommodating a large number of survivors impractical.
Instead, submarines may facilitate rescue by relaying the location of survivors to other vessels or authorities. This practice is recognized in legal commentary on submarine warfare. The swift response of the Sri Lankan navy, which rescued 32 sailors and recovered 87 bodies from the IRIS Dena, suggests that authorities were promptly informed of the incident. It is likely the US Navy transmitted the location of the survivors, as the damaged state of the Iranian vessel would have prevented the crew from sending a distress signal themselves.
