The Sinking of the IRIS Dena: Escalation at Sea, Human Cost, and the Erosion of Humanitarian Restraint

On March 18, in Tehran, thousands gathered for funeral processions honoring victims of the ongoing war, including the sailors of the IRIS Dena, whose deaths have become a symbol of the widening scope and human cost of the conflict. The ceremonies, beginning at Enghelab Square and continuing toward Meraj al-Shohada, reflect a moment of national mourning that underscores how deeply this war is affecting the Iranian public.

Among those mourned were the sailors of the IRIS Dena, an Iranian naval vessel sunk on March 4, 2026 in the Indian Ocean by a U.S. submarine torpedo attack. At least 87 sailors were killed, with only 32 survivors from a crew of approximately 130. Many of the victims were young personnel who had just days earlier participated in the MILAN 2026 multinational naval exercise in India, an event centered on maritime cooperation and international engagement. Iran has claimed that the Dena was unarmed, amplifying concerns that the vessel may have been illegally targeted.

The transformation of these sailors, from participants in an international naval gathering to victims of a sudden and devastating attack, highlights a troubling dynamic: the line between spaces of cooperation and zones of conflict is rapidly eroding. This concern is further intensified by public rhetoric surrounding the war. President Trump recounted a debate he had with military commanders in public, during which he suggested that Iranian vessels could have been captured rather than sunk. However, the President said he was told ‘It’s more fun to sink them,’ with the President stating “They like sinking them better.” This underscores that the use of lethal force against Iranian targets is being treated with insufficient gravity. In the context of an ongoing armed conflict, such language can undermine confidence in the careful application of international humanitarian law and the principle of restraint, which also amplifies risks against U.S. servicemembers who could be illegitimately targeted.

From a human rights perspective, the sinking of the Dena raises serious concerns not only regarding the scale of loss of life, but because it reflects a broadening geographic scope of hostilities. The attack reportedly occurred near Sri Lanka, in an area widely used for international maritime transit and outside the immediate core of active hostilities. This expansion increases risks for civilian shipping, regional stability, and neutral states, while reinforcing the perception that large areas of international waters are becoming zones of active conflict.

Under international humanitarian law (IHL), the legal framework governing naval warfare is complex but relatively well established. As a general matter, enemy warships are considered lawful military targets in war, provided they are not in neutral territorial waters and have not been rendered hors de combat. Here, there are indications that the Dena should not have been considered a lawful target, given it was not yet in an area of active hostilities and may have been unarmed. Moreover, given that the Iran war was launched without UN authorization, targets that might otherwise be considered permissible under the law of war - such as naval vessels at sea - might otherwise be considered an illegitimate target for the use of force.

Compliance with IHL requires more than identifying a lawful target. It also requires adherence to the principles of military necessity, proportionality, and precautions in attack. Even when a target is lawful, an attack must be intended to achieve a concrete and direct military advantage, and the expected harm must not be excessive in relation to that advantage. The reported use of a heavy torpedo, which caused the vessel to sink within minutes, resulted in rapid and widespread loss of life, leaving limited opportunity for evacuation. This underscores the importance of the obligation to take all feasible precautions to minimize harm, particularly when the foreseeable consequences of an attack include high casualties.

In addition, international humanitarian law imposes obligations after an attack has taken place. Under the Second Geneva Convention, parties to a conflict must, without delay and as far as feasible, take steps to search for, collect, and care for the shipwrecked. While submarine operations present operational constraints that may limit immediate rescue capabilities, these constraints do not eliminate the obligation itself. Available information indicates that regional actors, including Sri Lanka and India, played a central role in rescue operations, which raises reasonable questions about whether all feasible measures were taken by the attacking party to facilitate or support those efforts.

The broader implications of the incident extend beyond the immediate tragedy. The expansion of naval warfare into areas such as the Indian Ocean - far from traditional theaters of combat - places increased pressure on neutral states, complicates regional security dynamics, and raises the risk of miscalculation or unintended escalation. It also challenges long-standing expectations about the geographic limits of armed conflict and the protection afforded to areas not directly engaged in hostilities.

Questions regarding the assessment of military necessity, the proportionality of the attack, the precautions taken, and the fulfillment of post-strike obligations warrant careful and independent examination. Ultimately, the sinking of the IRIS Dena - and the funerals taking place - serve as a powerful reminder that armed conflict is not only a legal framework, but a human reality. Sailors who recently stood in formation in a setting of international cooperation are now being laid to rest. Without continued emphasis on restraint, accountability, and the protection of human life, the gap between what is legally permissible and what is morally sustainable risks growing wider—undermining both the law itself and the stability it is meant to protect.