In a dramatic escalation of the 2026 Iran-US conflict, the Iranian Navy frigate IRIS Dena was torpedoed and sunk by an American submarine in the Indian Ocean on March 4, 2026 — marking a historic moment in modern naval warfare.
The IRIS Dena was struck approximately 40 nautical miles off the coast of Galle, Sri Lanka, while returning home after participating in India’s International Fleet Review 2026 naval exercises.
The US submarine launched a Mark 48 heavyweight torpedo, confirmed by Chairman of the Joint Chiefs Gen. Dan Caine at a Pentagon briefing. This marks the first time since the end of World War II that a US Navy submarine has torpedoed and sunk an enemy combatant vessel.
US Defense Secretary Pete Hegseth described IRIS Dena as a “prize ship,” stating the sinking demonstrates the US-Israeli military operation against Iran stretching beyond its borders.
US officials confirmed that American forces have sunk more than 20 Iranian naval vessels since the conflict began, effectively dismantling Iran’s conventional surface fleet.
At the time of the incident, approximately 180 people were on board. The Sri Lankan Navy responded to a distress call and rescued 32 survivors, recovering 87 bodies, while over 60 crew members remain missing.
When Sri Lanka’s navy arrived at the location, there was no sign of the ship — only patches of oil and sailors floating in the water.
The Iranian Ambassador to India stated the vessel was “unarmed and in a regular maneuver at sea,” as Milan exercises required ships to operate under “peace protocol.”
India, which hosted IRIS Dena at its naval exercises just days prior, has yet to publicly criticise the attack, raising questions about its role as a self-declared “guardian of the Indian Ocean.”
Sri Lanka reaffirmed its neutrality in the conflict, while a second Iranian vessel, tanker IRIS Bushehr, sought refuge in Sri Lankan waters, with its 208 crew members evacuated to Colombo.
