IRIS Dena ship sunk by US Submarine torpedo: Why was the Iranian ship in the Indian Ocean?

A US submarine torpedoed and sank Iran’s IRIS Dena in the Indian Ocean within Sri Lanka’s Exclusive Economic Zone (EEZ), about 40 km off the country’s southern coast near Galle, killing at least 87 sailors and rescuing 32 others, Sri Lankan authorities said. The incident has drawn attention not only for its military escalation as the Iran-Israel war enters its sixth day but also for the presence of the Iranian warship in waters close to India, where such deployments have been rare.

Iran’s foreign minister said the United States will “bitterly regret” the precedent it has set, adding that the frigate Dena, described as a guest of India’s navy carrying almost 130 sailors, was struck in international waters without warning by the US, Reuters reported.

Why IRIS Dena was in the Indian Ocean

The IRIS Dena had been participating in diplomatic naval engagements in India in the weeks before it was sunk. The warship took part in the International Fleet Review (IFR) and the multilateral naval exercise Milan-2026, both organised by the Indian Navy in February.


The IFR is a large-scale naval parade involving warships, submarines, aircraft and personnel from multiple countries. Milan-2026, a biennial exercise hosted by India, aims to foster professional interaction and mutual trust among maritime partners. More than 85 ships from 74 countries participated, including vessels from the United States and Iran.

Following the Fleet Review on February 18, the Iranian frigate docked at the Indian port city of Visakhapatnam on February 20. Its presence in the Indian Ocean was linked to these diplomatic and multilateral engagements rather than routine combat deployment.

About the IRIS Dena

First launched in 2015 and attached to Iran’s Southern Fleet, the IRIS Dena was tasked with operations in the Strait of Hormuz and the Gulf of Oman. It was one of the newest frigates in the Iranian navy and was equipped with surface-to-air missiles, anti-ship missiles, torpedoes, heavy guns, radar systems and a helicopter landing pad. The vessel was named after Mount Dena in southwestern Iran.

The ship had been sanctioned by the U.S. Treasury Department in February 2023, along with executives of an Iranian drone manufacturer accused of supplying weapons to Russia for use in Ukraine.

Sri Lanka’s rescue and recovery operation

Sri Lanka’s navy said it received a distress signal from the vessel, which had 180 personnel on board, and immediately deployed ships and aircraft for a rescue mission. However, by the time naval units reached the location, there was no visible sign of the ship, only oil patches and life rafts in the water.

Rescue teams found survivors floating at sea and brought 32 personnel ashore. The injured were admitted to the National Hospital in Galle, where one was reported to be in critical condition, seven were receiving emergency treatment and others were treated for minor injuries.

The navy also recovered 87 bodies, which were transported to land. At the hospital in Galle, bodies were brought in trucks and placed in a makeshift mortuary under security provided by Sri Lankan police and naval personnel.

Indian reactions

International relations analyst Zorawar Daulet Singh said the proximity of the strike to Indian waters was significant. He noted that Iranian missile activity had pushed the U.S. Navy closer to India and referred to the logistics agreement between India and the United States, cautioning that the repercussions for India of becoming even an inadvertent war party in an aggressive intervention would be dangerous. He said the Indian government must act independently and intelligently to safeguard national interests.