The final voyage of the Iranian warship sunk by the US

On 17 February, the Indian Navy welcomed the Iranian warship IRIS Dena to the port of Visakhapatnam for an international naval gathering. 

Photographs shared on social media showed the grey frigate entering harbour as sailors in white uniforms stood on deck.

The message celebrated cooperation at sea, using hashtags such as "Bridges of Friendship" and "United Through Oceans."

Just over two weeks later, the same vessel lay at the bottom of the Indian Ocean.

According to the BBC, the Dena was torpedoed by a United States submarine on 4 March near Sri Lanka's southern coast, killing most of the crew and sharply escalating tensions between Washington and Tehran.

US Defence Secretary Pete Hegseth later said the ship had believed it was safe in international waters but ultimately "died a quiet death," the BBC reports.

Commissioned in 2021, the Dena was a relatively new Moudge-class frigate belonging to Iran's Southern Fleet. These ships are typically used to patrol strategic waterways such as the Strait of Hormuz and the Gulf of Oman.

At the time of the attack, the warship carried about 130 sailors. The BBC reports that Sri Lankan rescue teams have recovered at least 87 bodies, while only 32 sailors survived.

Although the strike took place in international waters outside India's jurisdiction, it has created an uncomfortable diplomatic moment for New Delhi.

Retired Vice Admiral Arun Kumar Singh told the BBC that the expansion of the conflict into nearby waters was worrying. "The war has come to our doorsteps. That is not a good thing," he said.

Strategic affairs expert Brahma Chellaney also raised concerns about the broader implications.

According to the BBC, he described the US strike in India's maritime neighbourhood as a "strategic embarrassment" that effectively turned waters near India into a potential war zone.

The situation is particularly sensitive because the Dena had recently been a diplomatic guest of the Indian Navy.

The warship had travelled to Visakhapatnam to take part in the International Fleet Review 2026 and Exercise Milan, a large multinational naval exercise designed to showcase India's maritime partnerships.

The BBC reports that the event brought together representatives from 74 countries and 18 naval vessels, reflecting India's ambition to become the Indian Ocean's "preferred security partner."

Ships participating in multinational exercises usually do not carry full combat loads of live ammunition unless specific drills require them. 

Even during live-fire exercises, vessels typically carry only limited ammunition designated for training purposes, the BBC notes.

Vice Admiral Singh, who attended the event, told the BBC he had seen the Iranian sailors marching during a parade along the Visakhapatnam seafront only days before the ship's destruction.

"All young people," he said. "I feel very sad."

The participating vessels left port on 21 February for the sea phase of Exercise Milan, which ran until 25 February. What happened to the Dena afterwards remains unclear.

According to the BBC, the frigate may have either returned briefly to port or separated from the group after the drills ended.

The warship was later attacked about 20 nautical miles west of Galle, in Sri Lankan waters designated for search-and-rescue operations.

Singh told the BBC that the United States likely tracked the vessel's movements. The US Navy monitors maritime traffic worldwide, and analysts say a significant portion of its submarine fleet remains deployed at sea at any given time.

Experts believe the submarine used a Mark-48 torpedo, a powerful weapon capable of carrying roughly 650 pounds of explosives. The BBC reports that the torpedo may have been fired from a distance of three to four kilometres in the early hours of the morning.

The explosion was devastating. According to the BBC, the warship sank within two to three minutes, leaving little time for the crew to escape. 

Despite the speed of the disaster, the sailors managed to send an SOS signal that was received by Sri Lanka's Maritime Rescue Coordination Centre in Colombo.

Sri Lanka's navy launched the initial rescue operation, while India later deployed surveillance aircraft and naval vessels to assist the search effort, the BBC reports.

Under international law, countries at war are expected to attempt rescues of shipwrecked sailors when possible.

However, the BBC notes that submarines rarely surface after attacks because doing so would reveal their position.

For India, the diplomatic implications remain complicated. The country has strengthened defence ties with the United States in recent years while also maintaining long-standing political and economic relations with Iran.

Prime Minister Narendra Modi has called broadly for "dialogue and diplomacy" to resolve global conflicts but has not directly commented on the sinking.

Iran, meanwhile, has condemned the attack as an "atrocity at sea," emphasising that the destroyed frigate had recently been "a guest of India's Navy," according to the BBC.

Analysts say the incident highlights both the widening reach of the US-Iran confrontation and the limits of India's ability to control its strategic environment in the Indian Ocean region.