TNI Bureau: On 4 March 2026, the Iranian Navy frigate IRIS Dena, which had been returning from participation in naval exercises in India, sank in the Indian Ocean off the southern coast of Sri Lanka. The vessel issued a distress call in the early hours before going down in international waters about 40 nautical miles south of Galle.

According to statements by U.S. Defense Secretary Pete Hegseth, a torpedo fired from a United States Navy submarine struck the frigate during its transit, marking one of the rare modern uses of submarine-launched torpedoes against a surface warship. The U.S. has characterized the strike as part of ongoing military operations that include pressure and counter-actions involving Iranian forces.

Sri Lankan authorities coordinated a search and rescue operation after receiving the distress call. As of reports on the incident, at least 87 bodies have been recovered, and 32 sailors were rescued and taken to hospitals in Galle for treatment. Hundreds of personnel were believed to have been aboard when the frigate sank; the exact number of missing remains uncertain.

The IRIS Dena had recently taken part in the International Fleet Review 2026 and related naval events hosted by India, highlighting its role in regional maritime cooperation before the tragedy.

The sinking has drawn international attention for its strategic and humanitarian implications, as it expands the geographical scope of military conflict involving Iran and the United States beyond the Middle East and into the Indian Ocean theatre. Official reactions from Iran have condemned the attack, while diplomatic and military responses from other nations are continuing to unfold.