U.S. Submarine Sinks Iranian Frigate IRIS Dena Amidst Rising West Asia Tensions

On March 4, 2026, a United States submarine torpedoed and sank the Iranian frigate IRIS Dena in the Indian Ocean, approximately 40 nautical miles off the coast of Galle, Sri Lanka. This marks the first instance of an American submarine sinking an enemy vessel with a torpedo since World War II . The incident occurred as the IRIS Dena was returning home after participating in India’s International Fleet Review 2026 in Visakhapatnam .

Details of the Sinking

The IRIS Dena, a domestically produced vessel and a point of pride for the Iranian Navy, was struck by a single Mark 48 heavyweight torpedo . The Pentagon released infrared footage of the event, which U.S. Secretary of Defence Pete Hegseth described as a “quiet death” . The explosion caused a fracture in the frigate’s keel, sending a large plume of water into the air .

Casualties and Rescue Efforts

The sinking resulted in the deaths of 87 Iranian sailors. However, 32 survivors were rescued . Sri Lankan authorities have confirmed the vessel was a Moudge-class frigate .

International Law and Regional Implications

The strike has raised questions regarding compliance with international law and naval warfare norms, particularly as tensions in West Asia continue to escalate . Alongside the IRIS Dena, the Iranian oiler IRIS Booshehr is currently interned in an Indian port, and the frigate IRIS Dena (75) is also stricken .

Further Developments

The United States is reportedly urging Sri Lanka not to repatriate the 32 survivors of the IRIS Dena and the crew of the IRIS Booshehr to Iran . The United Arab Emirates is also considering freezing Iranian assets amid the escalating conflict between the U.S., Israel, and Iran .