On March 4, 2026, a United States Navy submarine fired a torpedo that sank the Iranian frigate IRIS Dena in international waters about forty nautical miles off Galle, in southern Sri Lanka. The incident marked a significant escalation in the ongoing conflict involving the United States, Israel, and Iran, which had intensified after coordinated military operations began in late February.
The Dena, a Moudge-class frigate of the Islamic Republic of Iran Navy, was among the country’s more modern surface combatants. At the time of the attack, it had been returning home after participating in the International Fleet Review 2026, a multinational naval exercise hosted by India in Visakhapatnam on the Bay of Bengal.
Sri Lankan officials reported that the vessel issued a distress call early on March 4 before sinking. The navy responded quickly, deploying ships and aircraft for search and rescue operations. However, by the time they reached the area, the frigate had already gone down.
U.S. Defense Secretary Pete Hegseth confirmed that the strike was carried out using a Mark 48 heavyweight torpedo launched from a U.S. submarine. He described the attack as the first of its kind by the United States against an enemy vessel since World War II, highlighting the rarity of such engagements in modern naval warfare.
Sri Lankan authorities recovered at least 87 bodies and rescued 32 injured sailors, who were taken to hospitals in Galle. With an estimated crew of about 180 on board, many remained missing and were presumed dead as search efforts continued.
Iran strongly condemned the attack. Foreign Minister Abbas Araghchi called it an “atrocity at sea” and accused the United States of escalating tensions without warning. He stressed that the Dena had been sailing in international waters and was not engaged in combat at the time.
India confirmed that the frigate had participated in its multinational naval exercise, which included representatives from over 70 countries. However, New Delhi did not immediately comment on the sinking, despite growing international attention.
Sri Lanka also reported the presence of a second Iranian vessel in the area. President Anura Kumara Dissanayake announced that the ship would be escorted to Trincomalee under Sri Lankan supervision to ensure the safety of its crew, reflecting the country’s neutral and humanitarian approach.
The incident raised legal and diplomatic concerns about the use of force against warships in international waters. While U.S. officials defended the strike as part of a broader military strategy, critics warned it could widen the conflict and threaten global stability.
The sinking also increased concerns over the security of vital shipping routes in the Indian Ocean. Several nations responded by boosting naval patrols to protect commercial traffic and monitor developments.
Iran has vowed retaliation, while international leaders have urged restraint. Analysts believe the sinking of the IRIS Dena could shape future naval strategy and stands as a stark reminder of how modern conflicts can quickly expand beyond their original regions.
