On March 4, 2026, a United States Navy submarine sank the Iranian frigate IRIS Dena with a torpedo strike in international waters roughly 40 nautical miles off the southern coast of Sri Lanka near Galle. The attack occurred amid the escalating conflict involving the United States, Israel, and Iran that intensified following coordinated military operations launched in late February.The Dena, a Moudge-class frigate in the Islamic Republic of Iran Navy, had recently participated in India’s International Fleet Review 2026 naval exercises in Visakhapatnam and was believed to be returning home when it was struck. Sri Lankan authorities reported that the ship transmitted a distress call early on March 4 before sinking in the deep waters of the Indian Ocean.
At a Pentagon briefing, U.S. Defense Secretary Pete Hegseth confirmed that an American submarine fired a Mark 48 heavyweight torpedo that destroyed the vessel. He described the strike as the first torpedo attack on an enemy warship since World War II, emphasizing how rare such engagements have become in modern naval warfare.Sri Lanka’s navy responded quickly with aircraft and ships after receiving the distress signal. By the time rescuers arrived, however, the frigate had already sunk. Officials recovered at least 87 bodies and rescued 32 injured sailors from the water, transporting them to hospitals in Galle. With an estimated crew of around 180 aboard the vessel, many sailors remain missing and are presumed dead.
The incident dramatically widened the geographic scope of the conflict, shifting attention to the Indian Ocean. Iranian Foreign Minister Abbas Araghchi condemned the strike, calling it an “atrocity at sea” and accusing the United States of attacking a ship sailing in international waters without warning.Sri Lanka also reported a second Iranian vessel in the area following the sinking. President Anura Kumara Dissanayake announced that Sri Lanka’s navy would escort the ship to the port of Trincomalee and temporarily take custody of it to ensure safety.International concern has grown following the attack, particularly over the security of vital Indian Ocean shipping routes. Several countries have increased naval patrols in the region while diplomats and legal experts debate the implications of targeting a warship in international waters.As tensions continue to rise, the sinking of the IRIS Dena is already being viewed as one of the most significant naval incidents of the 2026 Iran conflict and a potential turning point in how the war could expand beyond the Middle East.
