On March 4, 2026, a United States Navy submarine launched a torpedo strike that hit the Iranian frigate IRIS Dena, causing the vessel to sink in international waters roughly forty nautical miles off the southern coast of Sri Lanka near Galle.
The incident occurred amid the broader conflict involving the United States, Israel, and Iran, which escalated after coordinated military operations began in late February 2026.
The IRIS Dena, a Moudge-class frigate belonging to the Islamic Republic of Iran Navy, was among the more modern surface warships in Iran’s fleet. Prior to the attack, the vessel had been returning to Iran after participating in the International Fleet Review 2026 naval exercises hosted by India in Visakhapatnam along the Bay of Bengal.
Sri Lankan authorities reported that the frigate issued a distress signal early on March 4 before disappearing beneath the water, prompting an immediate search and rescue effort.
During a Pentagon briefing, U.S. Defense Secretary Pete Hegseth confirmed that a U.S. submarine had fired a Mark 48 heavyweight torpedo, which struck and sank the vessel in deep waters of the Indian Ocean.
Hegseth described the engagement as the first torpedo attack of this kind against an enemy warship since World War II, highlighting how uncommon such naval combat has been in recent decades.
Sri Lanka’s navy responded quickly to the distress call, deploying both ships and aircraft to the area. However, by the time rescue teams arrived, the frigate had already gone down.
Officials reported that 87 bodies were recovered from the sea, while 32 injured sailors were rescued and transported to hospitals in Galle for medical treatment.
Many crew members remained missing in the aftermath. Estimates suggested that roughly 180 sailors were aboard the Dena, leaving a significant number unaccounted for and presumed dead.
The destruction of the Iranian frigate quickly became one of the most dramatic naval incidents of the 2026 conflict, extending the scope of military activity beyond the Middle East and into the wider Indian Ocean region.
Military experts noted that submarine torpedo attacks on surface warships are extremely rare in modern warfare, underscoring the seriousness of the confrontation.
Iran’s Foreign Minister Abbas Araghchi condemned the strike on social media, describing it as an “atrocity at sea” and accusing the United States of escalating the conflict.
Araghchi stated that the frigate had been traveling in international waters and warned that the attack could set a dangerous precedent for naval engagements.
Iranian officials also emphasized that the vessel had recently taken part in a multinational naval gathering hosted by India, where it had been present as a participant in the fleet review.
Indian authorities confirmed that the International Fleet Review 2026 included ships from more than seventy countries and was intended to promote maritime cooperation.
However, the presence of the Iranian warship at the event later became politically sensitive following the attack. India had not immediately issued a public statement regarding the sinking by U.S. forces.
Sri Lankan officials reported that another Iranian naval vessel was also present in nearby waters after the incident.
Sri Lankan President Anura Kumara Dissanayake announced that the country’s navy would assist the second Iranian ship and escort it safely to the port of Trincomalee.
Authorities said the decision reflected Sri Lanka’s neutral stance and humanitarian commitment to helping sailors in distress.
The second vessel, identified as IRIS Bushehr, was placed under Sri Lankan naval supervision as the situation continued to unfold.
The sinking of the IRIS Dena triggered concern internationally, as it demonstrated how the conflict involving Iran was expanding into broader maritime regions.
Several governments expressed worries about the safety of major shipping routes in the Indian Ocean, which are vital to global trade.
European and allied naval forces subsequently increased patrols in the region to reassure commercial shipping operators and monitor potential escalation.
The event also sparked debate among international law experts regarding the legality of attacking a warship in international waters.
Some specialists argued that the circumstances surrounding the strike would need careful examination to determine whether the action complied with established maritime conventions.
U.S. military officials defended the operation, stating that it was part of a broader effort to weaken Iran’s naval capabilities during active hostilities.
Critics, however, warned that such actions could expand the conflict further and potentially draw additional countries into the confrontation.
Iranian leaders vowed that the attack would not go unanswered, reiterating Tehran’s intention to continue military operations against U.S. and allied forces.
The wider conflict had already caused significant casualties and displacement across several regions, leading international diplomats to urge restraint.
Members of the United Nations and other neutral governments warned that continued escalation could threaten regional stability and global security.
Naval strategists suggested that incidents like the sinking of the Dena could shape future naval doctrine and influence international rules governing warfare at sea.
The situation also placed pressure on nearby nations to balance diplomatic neutrality with humanitarian responsibilities toward the affected sailors.
Sri Lanka’s rescue operations received praise from international observers for prioritizing the safety and treatment of survivors.
Medical teams in Galle worked to treat sailors suffering from burns, fractures, and severe shock after being pulled from the water.
Historians and naval analysts believe the destruction of the IRIS Dena will likely be studied for years as a rare example of a modern submarine torpedo sinking a major surface warship.
Experts say the event could influence both diplomatic negotiations and naval policy in the future.
In a conflict already marked by extensive military operations, the sinking of the frigate signaled a major expansion in the geographic scope of hostilities.
It served as a stark reminder that modern conflicts can rapidly spread beyond their original regions, affecting distant seas and nations not initially involved in the confrontation.
