Attack on IRIS Dena

On the early morning of 4 March 2026, the Iranian Navy frigate IRIS Dena (F-75), a Moudge-class light frigate of the Islamic Republic of Iran Navy (IRIN) Southern Fleet, was struck by a torpedo and sank in international waters of the Indian Ocean, approximately 19 nautical miles (35 km) south of Galle, Sri Lanka. A U.S. Navy nuclear-powered fast-attack submarine fired the weapon. The sinking occurred during the 2026 U.S.–Iran war and was the first combat sinking of an enemy surface vessel by a U.S. Navy submarine since the Pacific theater of World War II.

Distress call time: 05:08 Sri Lanka Standard Time (UTC+05:30).The vessel sank within approximately 2–3 minutes of the torpedo strike.

Summary of Event

IRIS Dena was returning from the International Fleet Review 2026 and the multinational MILAN-26 exercise, both hosted by the Indian Navy at Visakhapatnam from 15 to 25 February 2026. On 26 February, the Iranian embassy in Sri Lanka requested a "goodwill visit" for Dena and two other Iranian ships starting 9 March.

On 28 February 2026, the United States and Israel initiated Operation Epic Fury — large-scale air strikes against Iranian targets. The Sri Lankan government then informed Iran, citing the Hague Conventions of 1899 and 1907 on neutral powers, that it would only allow belligerent ships to dock in cases of emergency. Iranian ships in the Indian Ocean subsequently requested docking at the Port of Kochi, India.

It is not publicly established why IRIS Dena continued toward Sri Lanka on 3 March. In the early hours of 4 March, while still in international waters, Dena was struck by a single Mk 48 heavyweight torpedo, sank within minutes, and issued a distress call reporting an explosion. The Sri Lanka Navy and Sri Lanka Air Force conducted search and rescue. By the time Sri Lankan responders reached the area, there was no ship — only an oil slick, life rafts, and sailors in the water.
Casualty figures as reported: approximately 180 crew on board, 87 bodies recovered, 32 sailors rescued. The U.S. stated it did not provide a warning prior to the strike.
A U.S. Navy Los Angeles-class nuclear attack submarine (SSN) fired two Mk 48 heavyweight torpedoes at IRIS Dena; one struck the frigate. The Pentagon publicly released infrared periscope video showing a massive detonation at the stern of Dena before the vessel sank. The video is consistent with a Mk 48 ADCAP under-keel detonation — the weapon is designed to explode beneath the ship's keel and break its back through hull whip caused by the collapsing gas bubble, rather than by direct hull penetration.

The strike took place during Operation Epic Fury, nominally a CENTCOM / U.S. 5th Fleet operation, despite the engagement happening in what is ordinarily U.S. 7th Fleet / Indo-Pacific Command battlespace. Chairman of the Joint Chiefs Gen. Dan Caine said U.S. forces had destroyed more than 20 Iranian naval vessels during Epic Fury and that the Iranian Navy was "combat ineffective" in theater.