U.S. Submarine Sinks Iranian Warship IRIS Dena Off Sri Lanka, Another Vessel Taken into Custody

A United States submarine has sunk the Iranian warship IRIS Dena in international waters off the coast of Sri Lanka, resulting in significant casualties. Separately, Sri Lanka took custody of another Iranian naval vessel, the IRIS Bushehr, after it reported an engine failure and sought assistance near Sri Lankan waters. These events have drawn international attention and reactions from various states, including Iran, the U.S., Sri Lanka, India, and Australia.

Sinking of the IRIS Dena

The Iranian warship, identified as the frigate IRIS Dena, was torpedoed by a U.S. submarine on March 4. The incident occurred in international waters, approximately 20 to 44 nautical miles off Sri Lanka's southern coast, near the city of Galle. The IRIS Dena was reportedly returning to Iran after participating in the "International Fleet Review" and "MILAN 2026" multilateral naval exercises, hosted by India in Visakhapatnam from February 15 to February 25. These exercises involved at least 74 countries, including the U.S. Navy.

The U.S. Department of Defense released a video showing the torpedo attack. U.S. Defense Secretary Pete Hegseth stated the sinking demonstrated the extension of U.S.-Israeli military operations against Iran beyond its borders.

U.S. Defense Secretary Pete Hegseth described the sinking as a "major blow" to Iran's navy.

U.S. President Donald Trump has indicated that disabling Iran's navy is a key objective, citing concerns about Iran's alleged attempts to close the Strait of Hormuz. Hegseth's claim that this was the first submarine sinking of a warship since World War II has been contested by historical accounts.

The IRIS Dena was characterized as one of Iran's newer warships. It was equipped with heavy guns, surface-to-air missiles, anti-ship missiles, and torpedoes, with the capability to carry a helicopter.

Casualties and Rescue Efforts

Reports on the IRIS Dena's crew size ranged from approximately 130 to 180 members. Sri Lankan authorities rescued 32 sailors and recovered 87 bodies from the incident site. An estimated 60 to over 100 sailors remain unaccounted for.

The Sri Lankan navy received a distress call between 6 a.m. and 7 a.m. (00:30 to 01:30 GMT) on March 4 and dispatched ships and air force planes for rescue operations. Rescuers found oil patches and sailors in the water, but no sign of the ship itself. The rescued mariners were transported to a hospital in Galle.

India's navy also received a distress signal, noting that Sri Lankan rescue efforts were already in progress. Iranian embassy officials have since sent two officers to Galle to gather information from the survivors.

Custody of the IRIS Bushehr

On March 8, Sri Lanka initiated the transfer of over 200 sailors from another Iranian naval vessel, the IRIS Bushehr, to shore. The IRIS Bushehr, identified as a navy logistics ship with a helicopter pad, had requested assistance while anchored outside Sri Lankan waters due to a reported engine failure.

Approximately 204 to 208 sailors were transported to Welisara Naval Base near Colombo for border control procedures and medical tests, with no health issues detected. About 15 crew members remained aboard the ship with Sri Lankan naval personnel to assist with operational instructions and manuals. The IRIS Bushehr is slated for transfer to the port of Trincomalee in eastern Sri Lanka and will remain in Sri Lankan custody until further notice.

Sri Lankan President Anura Kumara Dissanayake stated that the decision to take control of the IRIS Bushehr was made after discussions with Iranian officials and the ship's captain, citing the engine failure.

President Dissanayake affirmed that Sri Lanka's actions were conducted under international treaties and conventions, emphasizing the country's neutrality and humanitarian principles.

A former Sri Lankan foreign secretary supported these actions, citing adherence to the Law of the Sea and The Hague Convention.

International Reactions and Implications

Iran

Iranian Foreign Minister Abbas Araghchi described the sinking of the IRIS Dena as an "atrocity at sea" and stated that the U.S. "will come to bitterly regret" the attack. He also highlighted that the frigate had been a "guest of India's navy."

India

The incident generated discussion in India due to the IRIS Dena's participation in Indian-hosted naval exercises. While the Indian government initially maintained a reserved stance, Foreign Minister S Jaishankar later commented that the sinking was part of the "reality of the Indian Ocean."

Indian Foreign Minister S Jaishankar stated the Iranian sailors were "caught on the wrong side of events."

India has also provided emergency docking to three other Iranian vessels and housed their crew in Indian naval facilities. Opposition leaders in India criticized the government's initial silence and called for a more direct response. Analysts have raised questions about whether India was aware of the impending U.S. attack, which could have implications for U.S.-India strategic relations.

Australia

Australia's government confirmed that three Australians were aboard the U.S. submarine involved in the IRIS Dena incident. Their presence was part of a trilateral U.S., Australian, and British training program under the AUKUS security pact. The Australian government maintained that it was not informed in advance of any U.S. and Israeli plans to attack Iran, but supports the objective of preventing Iran from acquiring nuclear weapons. It also clarified that an Australian would not have been responsible for firing the torpedo.

International Law

A professor of International Law stated that the U.S. likely had the right to target the vessel under existing rules of engagement.

The professor noted that torpedoing a vessel far from Iran's territorial waters represents a significant expansion of the conflict's operational area into the Indian Ocean.

Regarding the IRIS Bushehr, an expert suggested that as a neutral state, Sri Lanka can grant port entry permission, and the vessel would then fall under Iranian jurisdiction, precluding Sri Lankan authorities from inspection unless Colombo aligned with the U.S.

The sinking of the IRIS Dena occurs amidst ongoing air strikes by the United States and Israel on Iran, following an attack that reportedly killed Supreme Leader Ali Khamenei. Tehran has responded with drone and missile attacks on Israel and U.S.-linked assets in Gulf countries.