NEW DELHI – Eight days after the conclusion of India’s biennial MILAN naval exercise off the coast of Visakhapatnam, one of the participating vessels was sunk in the Indian Ocean.
On March 4, 2026, IRIS Dena, a Mowj-class Iranian frigate, was torpedoed and sunk by a U.S. submarine approximately 40 nautical miles off the southern coast of Sri Lanka. Eighty-seven of the estimated 180 personnel on board were killed, while thirty-two survivors were recovered and transported to Karapitiya Teaching Hospital in Galle. U.S. Defense Secretary Pete Hegseth subsequently confirmed the attack, describing it as the first American submarine sinking of an enemy vessel since World War II.
The incident has prompted diplomatic discussions involving India. Indian defense officials and naval veterans have disputed any suggestion of Indian responsibility.
The sequence of events leading up to the incident is central to India’s position. IRIS Dena departed Visakhapatnam on February 25, with its last recorded port of call at Hambantota, Sri Lanka. The vessel was subsequently tracked operating in international waters, within Sri Lanka’s exclusive economic zone, for over eight days. The U.S.-Israeli military campaign against Iran, Operation Epic Fury, began three days after the conclusion of MILAN, with initial strikes recorded on February 28.
Regarding the immediate aftermath, the attack occurred within the jurisdiction of the Maritime Rescue Coordination Centre Colombo. Sri Lankan maritime authorities led the response operation. Upon notification, the Indian Navy activated search and rescue assets.
Indian officials have emphasized the vessel’s movements between its departure from India and the subsequent attack. They state that IRIS Dena’s eight-day presence in international waters reflects the nation’s operational choices rather than any association with the MILAN exercise. The United States, being in conflict with Iran, is likely to have considered any Iranian naval vessel a potential military target regardless of its location or port history.
The broader context of the conflict shapes this interpretation. The scale of U.S. naval action against Iran has been noted. Reports indicate that more than twenty Iranian or Iran-linked vessels have been struck since the conflict began. According to officials, IRIS Dena’s prominence in international commentary is due to its recent presence in Indian waters, not a substantive difference in India’s culpability.
The issue of legal jurisdiction has also been raised. Under established international maritime law, a host nation’s responsibility for a visiting foreign vessel extends only to its territorial waters. Once a vessel departs, it falls under the jurisdiction of the waters it subsequently enters.
India has not issued a formal statement. Defense and diplomatic circles consistently emphasize that MILAN was a multilateral exercise with many nations and that the subsequent bilateral conflict occurred in international waters beyond India’s involvement.
Ashu Mann
Ashu Mann is an Associate Fellow at the Centre for Land Warfare Studies. He was awarded the Vice Chief of the Army Staff Commendation card on Army Day 2025. He is pursuing a PhD in Defence and Strategic Studies. His research focuses include India-China territorial dispute, great power rivalry, and Chinese foreign policy.
