IRIS Dena, an Iranian Moudge-class frigate, was sunk by a United States submarine in the Indian Ocean off the coast of Sri Lanka on 4 March 2026. The vessel had recently participated in the Indian Navy’s International Fleet Review and the Milan multilateral maritime exercise in Visakhapatnam. The incident resulted in significant loss of life, with ongoing search and rescue operations for missing crew members.According to Deccan Herald, IRIS Dena was present in India as part of the Indian Navy’s premier multilateral exercise Milan, which included participation from 42 warships and submarines representing 18 foreign countries. The warship also featured in the International Fleet Review hosted by the Indian Navy in Visakhapatnam in February 2026, before departing for its return journey to Iran.As reported by Financial Express, the IRIS Dena was among 19 foreign naval ships at the International Fleet Review and was attacked in international waters while heading back to Iran. The Ministry of External Affairs of India has categorically denied claims that Indian ports were used by the US Navy for launching attacks on Iran, labelling such allegations as false and misleading.India’s 'Strategic' Silence on Israel–US War Against Iran May Prove CostlyRegional security concerns have intensified following statements from Sri Lankan Member of Parliament Namal Rajapaksa, who highlighted the implications for both Sri Lanka and India. He called for greater transparency from the Sri Lankan government regarding prior knowledge of the US military operation and urged regional dialogue on Indian Ocean security.The Sri Lankan Navy responded to a distress call from IRIS Dena and conducted rescue operations, recovering 87 bodies and rescuing 32 sailors, as detailed by officials. The incident occurred approximately 40 nautical miles south of Galle, within Sri Lanka’s search and rescue zone. The vessel was returning from its official engagement in India at the time of the attack.“An American submarine sank an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo,” stated US Defence Secretary Pete Hegseth at a Pentagon briefing, as cited in multiple official statements.Footage released by the US Department of Defense showed the moment the torpedo struck IRIS Dena, resulting in the vessel breaking apart and sinking rapidly. The video, as seen in coverage, confirmed the scale of the attack and the immediate aftermath, with Sri Lankan rescue teams finding only oil patches and life rafts upon arrival.Diplomatic and strategic implications for India have been noted amid ongoing tensions in the region. Analysts have pointed out that India, while not a party to the conflict, faces increased pressure to balance its relationships with both the United States and Iran, especially after hosting the Iranian vessel as an official guest.Further context on the broader conflict was provided in recent updates, which noted that the Iran-Israel-US conflict has led to disruptions in global energy trade and heightened security risks in the Indian Ocean, a region traditionally considered within India’s strategic sphere of influence.“This is about the national security of the Indian Ocean and about Sri Lanka, India, Bangladesh, the regional part of the world, Pakistan,” said Namal Rajapaksa, emphasising the need for regional cooperation.Analysis showed that the IRIS Dena was a modern warship equipped with advanced weaponry and had previously visited ports in Brazil and South Africa before its stop in India. The vessel’s participation in Indian Navy events was part of routine international naval cooperation, and its sinking marks a rare instance of a submarine-launched torpedo attack in recent decades.Reporting indicated that the Indian Navy continues to face its own challenges, including a significant shortfall in officer and sailor strength, which impacts its operational capacity and ability to respond to regional crises as highlighted in recent defence analyses.“The relatively lower number of sanctioned posts in the Indian Navy is structurally linked to fleet size, platform requirements, and government approvals rather than arbitrary limitation,” stated a senior Indian Navy official.Iran War Crisis: Repatriation Efforts On Amid Reports of Indians Killed, MissingNote: This article is produced using AI-assisted tools and is based on publicly available information. It has been reviewed by The Quint's editorial team before publishing.