On the morning of March 4, 2026, a US Navy submarine fired a torpedo at an Iranian warship in the Indian Ocean, off the southern coast of Sri Lanka. The ship, called IRIS Dena, sank shortly after. At least 87 sailors were killed, 32 were rescued, and around 100 others were still missing as of the latest reports.

The IRIS Dena was in international waters, roughly 40 nautical miles south of Galle, a port city in southern Sri Lanka. The ship had about 180 crew members on board and was on its way back to Iran after participating in a naval event in India.

At around 5:08 AM local Sri Lanka time, the IRIS Dena sent out a distress call reporting an explosion on board. The ship sank shortly after before rescue teams could reach it.

Sri Lanka's navy responded to the distress call and launched a joint search and rescue operation with the Sri Lanka Air Force. Rescuers recovered bodies from the water and brought 32 survivors to Karapitiya Teaching Hospital in Galle for treatment of blast injuries and exhaustion. Sri Lankan authorities confirmed that no other ships or aircraft were seen in the area at the time of the incident.

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Later that day, at a press briefing at the Pentagon in Washington, US Defense Secretary Pete Hegseth confirmed that an American submarine had carried out the attack. He said the submarine fired a Mark 48 heavyweight torpedo at the Iranian frigate. Hegseth described the strike as a "quiet death" and said it was the first time the US had sunk an enemy ship with a torpedo since World War II.

The IRIS Dena is a Moudge-class frigate — Iran's most modern class of domestically built warships. The ship was commissioned in 2021 and weighs around 1,500 tonnes. It is armed with anti-ship missiles, surface-to-air missiles, heavy guns, and lightweight torpedoes. It can also carry a helicopter.


In February 2026, just days before the attack, the IRIS Dena had been in India participating in the MILAN 2026 multinational naval exercise and the International Fleet Review at Visakhapatnam, on India's eastern coast. The Indian Navy had formally welcomed the ship when it arrived in February. The IRIS Dena was returning home to Iran when it was hit.

The fact that the ship had just been involved in a peaceful international naval exercise with multiple countries — including India — and was then sunk while sailing back, makes this event even more significant.

The ongoing conflict between the US, Israel, and Iran has mostly been fought in the Middle East — in the Persian Gulf, the Strait of Hormuz, and inside Iran. The sinking of the IRIS Dena off Sri Lanka marks the first time this conflict has extended into the Indian Ocean, which falls under the jurisdiction of the US 7th Fleet.

US military officials have stated that one of the main goals of Operation Epic Fury — the name of the US-Israel military operation against Iran — is to destroy Iran's naval capabilities. CENTCOM commander Admiral Brad Cooper said the US is focused on sinking the entire Iranian Navy, and that as of the time of his statement, there was not a single Iranian ship still operating in the Arabian Gulf, the Strait of Hormuz, or the Gulf of Oman.

Chairman of the Joint Chiefs of Staff General Dan Caine told reporters that the US had destroyed more than 20 Iranian naval vessels, including one Iranian submarine, since the operation began. The IRIS Dena was the largest ship sunk in the Indian Ocean in this conflict.

The sinking of the IRIS Dena is being called a historic event by military analysts for two reasons.

First, it is the first time since World War II that an American submarine has sunk an enemy surface warship using a torpedo. The last time this happened was in the final days of World War II, when the USS Torsk fired the US Navy's last torpedoes of the war against a Japanese ship in the Sea of Japan.

Second, it is only the second time in history that a nuclear-powered submarine has sunk an enemy vessel using a guided torpedo. The first was in 1982, when the British submarine HMS Conqueror sank the Argentine warship ARA General Belgrano during the Falklands War.

The Pentagon released a video, filmed through the submarine's periscope, showing the torpedo striking the IRIS Dena at the stern. The explosion lifted the rear of the ship out of the water before it began sinking.

Sri Lanka's Foreign Minister Vijitha Herath confirmed the rescue operation in parliament and said two navy vessels and one aircraft were sent to the area. The rescued Iranian sailors were transported to hospital in Galle, and police were stationed outside to manage the situation.

The sinking of the IRIS Dena shows that the US-Iran conflict is no longer limited to the Middle East. By taking out an Iranian warship in the Indian Ocean — thousands of kilometres away from the Persian Gulf — the US has signalled that it can track and target Iranian naval assets anywhere in the world.

For the region, this raises questions about the safety of international waters and what it means for other countries that share the Indian Ocean, including India, which had just hosted the IRIS Dena days before it was sunk.

Military analysts expect the conflict to continue escalating in the days ahead. US Central Command has said it will continue striking Iranian naval and military infrastructure over the next 48 to 72 hours.

As of now, the search and rescue operation near Galle is ongoing. The full human cost of the attack — including the final number of dead and missing — is still being determined.