On 16 February 2026,[11] the vessel sailed to India to participate in the International Fleet Review 2026 and the multinational naval exercise Milan held at Visakhapatnam.[12][13] Prior to the exercise, the Crew members had also embarked on a cultural visit of India, visiting the Taj Mahal and Kailashgiri as well as participating in a city parade.[14] The ship left Indian waters on 25 February.[11]
In late February 2026, there was a significant escalation in the conflict between a coalition led by Israel and the United States, and Iran, which included U.S.–Israeli airstrikes on targets within Iran from 28 February, and subsequent Iranian retaliation attacks on various countries in the Middle East.[15][16]
Naval action
Footage of IRIS Dena being struck (left) and sinking later (right), as released by the US Department of Defense
Dena was sunk in the early morning of 4 March 2026.[17] One media report indicates American forces warned Dena twice to abandon the ship before it was sunk.[18] According to the Sri Lankan Ministry of Foreign Affairs, Dena issued a distress call at 05:08 SLST, reporting an explosion, prompting an immediate search and rescue operation by the Sri Lanka Navy and Sri Lanka Air Force. The ship was returning to Iran from India, and was about 19 nautical miles (35km; 22mi) off the coast from Galle, Sri Lanka, in international waters, when the attack occurred.[19][20] The ship sank within 2-3 minutes of the attack.[21]
Hegseth states: "...[Dena] thought it was safe in international waters. Instead, it was sunk by a torpedo. Quiet death."[22][23]
During a briefing at The Pentagon, U.S. Secretary of Defense Pete Hegseth confirmed that Dena had been sunk by a US Navy submarine.[24][25] Other government officials specified that the submarine was USSCharlotte, which fired two Mark 48 torpedoes and hit Dena with one of them.[26] Hegseth, commenting on the engagement, stated: "[Dena] thought it was safe in international waters. Instead, it was sunk by a torpedo. Quiet death."[22][23] Australian Prime Minister Anthony Albanese later confirmed that three Royal Australian Navy personnel were on board the submarine.[27][28]
At the time of the incident, there were approximately 180 people on board the frigate,[29] including members of the Iranian Navy band.[30] Reports indicate that at least 87 individuals were killed in the attack, while at least 61 others remained missing. Thirty-two survivors were rescued by the Sri Lanka Navy and transported to the Galle National Hospital, where they received medical treatment for exhaustion and injuries related to the blast.[31][29]
According to an official press release by the Indian Navy, they were notified in the early hours by the Sri Lanka Navy of the distress call to the Maritime Rescue and Coordination Centre (MRCC) Colombo. India thereafter deployed INSTarangini and INSIkshak from Kochi as well as its P-8I Neptune long-range maritime patrol aircraft to search for survivors that evening. The P-8I was launched at 10:00 IST along with another aircraft equipped with air-droppable life rafts to support the search operations being led by the Sri Lankan authorities. Tarangini reached the designated search area by 16:00 IST but the Sri Lanka Navy and agencies had already begun operations. Ikshak remains deployed to assist in search operations in the region as of 5 March.[32][33][34]
The Sri Lanka Navy ended search operations on 8 March.[35]
Aftermath
Crew
The Sri Lanka Navy recovered 87 bodies of Iranian sailors. They were taken to Galle Hospital. The Iranian authorities have requested Sri Lanka to hand over all the bodies of the sailors who died in the attack on board IRIS Dena so they can be repatriated for final rites. Until arrangements are made, the remains will be stored in the hospital's cold rooms.[36][37] The residents of the city of Visakhapatnam who had hosted the crew during MILAN-26 also expressed their anguish and concern for the well-being of the Crew.[14]
Iran
The government of Iran has called the attack "an atrocity at sea."[38]
After the sinking of IRISDena, a second Iranian ship, IRISBushehr of the Bandar Abbas class, was requested to enter Colombo port. The Sri Lankan government stated that Sri Lanka will act under international conventions, including the 1982 UN Convention on the Law of the Sea to take custodianship of IRISBushehr. The ship was later interned by the Sri Lanka Navy with its crew of 208. This is the first instance of a warship being interned in a neutral country since World War II. The crew members of IRIS Bushehr, consisting of 53 officers, 84 cadet officers, 48 senior sailors and 23 sailors, were transferred to Colombo and the ship was moved to Trincomalee Harbour by the Sri Lanka Navy.[20][39][40]
It was also reported that the landing ship IRISLavan with a crew of 183 sailors had sought refuge and been interned at Kochi, India late evening on 4 March, following the attack on Dena.[41][42][43] The United States had urged Sri Lanka not to repatriate IRIS Dena survivors and IRIS Bushehr crew back to Iran so that Iran could not use them for propaganda. It also asked Sri Lanka if there were any attempts made to encourage defection among crew members.[44] The ship also emerged as a public curiosity in Kochi.[45] On 7 March, the Indian government said it had allowed IRIS Lavan to dock at Kochi on humanitarian grounds.[46]
United States
The incident has sparked a debate regarding potential violations of international law by the United States, specifically the Second Geneva Convention, amid allegations that U.S. forces left the scene without attempting to rescue survivors.[30][47] Academics who believe the submarine's actions were legal, argue that due to the lack of space within a submarine and risks of surfacing, submarines have been regarded as generally not having an obligation to engage in rescue operations, and that the attack was permitted due to the ongoing military conflict between Iran and the United States.[21][48] Academics who believe the submarine's actions were illegal, argue that the submarine had an obligation to do what it could to save the crews' lives,[30][47] and that the attack raises questions about the broader conflict's legality due to an expansion outside of imminent threats to the US.[49][50]
Australia
On 6 March, Australian Prime Minister Anthony Albanese acknowledged that three Australian Defence Force personnel were aboard the US submarine that sank IRIS Dena. He said that the Australian personnel were on board the submarine as part of a training rotation for the AUKUS security partnership, under which the United States will supply nuclear submarines to Australia. Albanese stated that Australian personnel did not participate in any "offensive action" against Iran.[51]
India
On 4 March 2026, Indian strategic affairs analyst Brahma Chellaney stated that the U.S. Navy's sinking of the Iranian frigate IRIS Dena in India's "maritime neighbourhood" was "more than a battlefield event; it is a strategic embarrassment for New Delhi."[52] Chellaney argued that by attacking a vessel returning from an Indian-hosted exercise, Washington transformed India's maritime neighbourhood into a "war zone," thereby challenging India's authority and its reputation as the preferred security partner in the Indian Ocean.[53]
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