US submarine sinks IRIS Dena after a torpedo strike in international waters off Sri Lanka, a major escalation in the wider US-Iran conflict. U.S. Defence Secretary Pete Hegseth confirmed the attack during a Pentagon briefing on March 4, 2026, as the US and Israel continue military operations against Iran.
The Pentagon also released video footage showing a torpedo launched from a US submarine striking the Iranian vessel, identified in reports as IRIS Dena, while it was underway near Sri Lanka’s southern coast.
US Submarine Sinks IRIS Dena: What We Know
US officials said the submarine used an MK-48 heavyweight torpedo to sink the Iranian warship, marking the first time since World War II that a US submarine has sunk a surface vessel with a torpedo.
Reports described the ship as operating off the coast of Sri Lanka near the coastal city of Galle when it transmitted a distress call, triggering rescue efforts by Sri Lankan authorities.
IRIS Dena was sunk by a US submarine with a MK-48 torpedo.
This is the first case in 85 years, of a warship being sunk by a sub that was also captured on tape.
Air superiority is essential for anti-submarine missions, and subs are extremely dangerous against ships, which is why… pic.twitter.com/n8QKfZd4uk
— Zhao DaShuai 东北进修🇨🇳 (@zhao_dashuai) March 4, 2026Officials in Sri Lanka said around 180 crew members were believed to be aboard. Rescue teams reported 32 survivors were pulled from the sea, while recovery efforts continued for the missing and deceased.
Multiple reports said IRIS Dena had recently participated in an international naval event in the region and was returning toward Iran when it was struck.
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The sinking is being framed as a rare modern example of submarine-on-surface warfare and a significant widening of the operational theatre beyond the Middle East. Analysts noted the incident could further raise tensions across key sea lanes in the Indian Ocean region.
Iran has not issued a detailed official response in the reports cited, while international attention has focused on the humanitarian aftermath and the potential for further escalation.
