North American submarine launched torpedo against IRIS Dena ship in the Indian Ocean; expert debates legality of action
The news that a United States submarine had torpedoed and sunk the Iranian warship IRIS Dena about 40 nautical miles –74 km– off Sri Lanka on Wednesday (March 4, 2026) took many observers by surprise. An attack like this, so far from the Persian Gulf — and on a key trade route linking China to the Middle East — suggests that the arena for this war may be widening.
But the incident also highlights something that is rarely well understood outside military and legal circles: the law of naval warfare. Many wonder: was this attack legal? And who had the obligation to rescue the survivors?
When does the law of naval war apply?
The law of naval war is a subset of the . It establishes permissions and protections for combatants, civilians and neutral actors involved in conflicts at sea.
It is important to emphasize that it applies regardless of whether the use of force was legal. In other words, you must follow the law of the sea even if your entire justification for war is not legal under international law.
Furthermore, the conduct of operations at sea is regulated by the law of naval warfare, regardless of whether war has been formally declared or not. It also takes precedence over the United Nations Convention on the Law of the Sea.
This reflects the principle of lex specialis in international law, meaning that the most specific body of law applies.
These rules developed over the centuries as states sought to regulate the conduct of conflicts at sea while at the same time allowing navies to operate effectively.
So was it legal for the US to sink the Iranian warship?
Yes, he was a legal target.
According to the law, warships belonging to a State involved in an international armed conflict are military objectives in nature. The rules say they can be legal targets.
These attacks can be carried out on the high seas or within the territorial waters of 12 nautical miles –22 km– of States that are party to the international armed conflict. This effectively means that this attack can take place anywhere outside the territorial waters of neutral states.
If the Iranian warship had been in Sri Lankan waters (i.e. within 12 nautical miles of the Sri Lankan coast) at the time, the attack would not have been legal.
But in this case, the IRIS Dena was operating outside Sri Lankan territorial waters and therefore constitutes a legal military target.
What does the law say about rescuing survivors?
The law of naval warfare also establishes obligations regarding the rescue of survivors.
According to , the parties to a conflict must –after each engagement– take all possible measures to search for and collect the shipwrecked, wounded and sick.
These rules apply to naval warfare and require belligerents, as far as military circumstances permit, to assist survivors at sea.
In practice, however, submarines face specific challenges in fulfilling this obligation. Rising to the surface to rescue survivors can expose them to significant risks. Furthermore, it is not normally possible to accommodate a large number of survivors on a submarine.
If a submarine cannot safely surface to rescue survivors, it can facilitate the rescue by reporting its location to other vessels or authorities. The rapid response of the Sri Lankan navy, which rescued 32 sailors from the IRIS Dena, suggests that authorities were quickly informed about the incident.
It is not yet clear how Sri Lankan authorities were informed, but it seems likely that the US Navy relayed the location of the survivors. Considering the damage sustained by the IRIS Dena and the reported casualties, it is unlikely that the ship’s crew were able to transmit its location on their own.
This may also explain why early reports suggested a submarine had sunk the ship, before the US confirmed its involvement.
It is also unlikely that the crew of the IRIS Dena knew immediately that they had been hit by a submarine-launched torpedo. This torpedo would normally be fired from far away, beyond the detection range of a ship’s hull-mounted sonar.
A legal military target
Although debate continues over the legal justification for the US entering into conflict with Iran, the conduct of hostilities at sea is nevertheless governed by the law of naval war.
Under this framework, IRIS Dena therefore constitutes a lawful military target, and efforts to facilitate the rescue of survivors are consistent with these obligations.
This text is republished from The Conversation under a Creative Commons license. Read the original.
