Summary: The Iranian warship Iris Dena was sunk by a US submarine in the Indian Ocean off Sri Lanka in early March, shortly after participating in a multilateral naval exercise hosted by India. The incident, resulting in significant casualties, is seen as a widening of regional conflict and presents a strategic dilemma for India, raising questions about its authority in its own maritime neighborhood.
Main Topics Covered:
1. The sinking of the Iranian warship by the US.
2. The diplomatic context of the ship's recent visit to India for a naval exercise.
3. The geopolitical implications and strategic embarrassment for India.
The final voyage of the Iranian warship sunk by the US
On 17 February, the Indian Navy posted a cheerful message on X.
"Welcome!" it wrote, greeting the Iranian warship Iris Dena as it steamed into the port of Visakhapatnam to join an international naval gathering.
Photographs showed sailors in crisp whites and a grey frigate gliding in the sea harbour on a clear day. The hashtags spoke of "Bridges of Friendship" and "United Through Oceans".
Two weeks later the ship, carrying 130 sailors, lay at the bottom of the Indian Ocean. It had been torpedoed by a US submarine off Sri Lanka's southern coast on 4 March.
Commissioned in 2021, the Dena was a relatively new vessel - a Moudge-class frigate of Iran's Southern Fleet, which patrols the Strait of Hormuz and the Gulf of Oman.
According to US Defence Secretary Pete Hegseth, the vessel "thought it was safe in international waters" but instead "died a quiet death". Rescue teams from Sri Lanka have recovered at least 87 bodies. Only 32 sailors survived.
The sinking marks a dramatic widening of the war between America, Israel and Iran. And, though it occurred in international waters of the Indian Ocean and outside India's jurisdiction, it is an awkward moment for Delhi.
"The war has come to our doorsteps. That is not a good thing," says retired Vice Admiral Arun Kumar Singh.
For some strategists, the episode carries broader implications for India's regional standing.
Indian strategic affairs expert Brahma Chellaney wrote on X that the US torpedoing of the Iranian warship in India's "maritime neighbourhood" was "more than a battlefield episode" - calling it a "strategic embarrassment" for Delhi.
"By sinking a vessel returning from an Indian-hosted multilateral exercise, Washington effectively turned India's maritime neighbourhood into a war zone, raising uncomfortable questions about India's authority in its own backyard," Chellaney wrote.
Just days before its destruction, the Dena had been a diplomatic guest of the Indian Navy.
The ship had travelled to Visakhapatnam, a sun-washed port city on India's east coast, to participate in the International Fleet Review 2026 and Exercise Milan, a large multilateral naval exercise meant to showcase India's growing maritime leadership.
Seventy-four countries and 18 warships took part in the events, which Delhi described as a demonstration of its ambition to become the Indian Ocean's "preferred security partner".
Visiting ships at such multilateral exercises usually do not carry a full combat load of live munitions, unless scheduled for a live-fire drill, according to Chellaney. Even during the sea phase, when drills and live firing take place, ships carry only tightly controlled ammunition limited to the specific exercises.
Singh, an invitee to the event, recalls seeing the warship and its Iranian sailors in Visakhapatnam just days before its fate changed.
"I saw the boys marching in front of me," he says of the Iranian naval contingent during the parade along the seafront, just 10m away. "All young people. I feel very sad."
He says on 21 February, the assembled ships - including the Iranian vessel - sailed out for the sea phase of Exercise Milan, scheduled to run until 25 February.
"What happened next is less clear: the ship may have returned to port or peeled away after exercises. Either way, the waters where it was later sunk - off Galle in Sri Lanka - lie only two to three days' sailing from India's east coast," Singh says. What the ship was doing in the 10-12 days in between is not clear.
Singh, who has commanded submarines, believes the sequence leading up to the attack was probably straightforward.
The US, he notes, tracks vessels across the world's oceans. "They would have known exactly when the ship left and where it was heading," he says. A fourth of America's submarine fleet of 65-70 is at sea at any given time, according to analysts.
According to the Indian Navy, the Iranian warship had been operating about 20 nautical miles west of Galle - roughly 23 miles (37km) - in waters that fall under Sri Lanka's designated search-and-rescue zone.
The attack, Singh says, appears to have involved a single Mark-48 torpedo, a heavyweight weapon carrying about 650 pounds of high explosive, capable of snapping a ship in two. Video footage suggests the submarine may have fired from 3-4km away, around 05:30 local time.
The aftermath was grim and swift.
The warship reportedly sank within two to three minutes, leaving little time for rescue. "It's a miracle they managed to send an SOS," Singh says, which was picked up by the Sri Lanka Maritime Rescue Coordination Centre in Colombo.
According to the Indian Navy, a distress call from the Iranian warship was picked up by Colombo in the early hours of 4 March, triggering a regional search-and-rescue effort.
The navy said in a statement that Sri Lanka's navy began rescue operations first, while India moved to assist later.
The Indian Navy deployed a long-range maritime patrol aircraft to support the search and kept another aircraft with air-droppable life rafts on standby.
A naval vessel already operating nearby reached the area by late afternoon. Another ship, which sailed from the southern Indian port city of Kochi to join the effort, continues to comb the waters for survivors and debris.
Under the Second Geneva Convention, countries at war are required to take "all possible measures" to rescue wounded or shipwrecked sailors after a naval attack. In practice, however, this duty applies only if a rescue can be attempted without putting the attacking vessel in serious danger.
Singh says submarines are rarely able to help.
"Submarines don't surface," he says. "If you surface and give up your position, someone else can sink you."
Singh suspects the speed of the sinking - and possibly sparse shipping in the area at the time - meant few nearby vessels could respond. "A ship breaking up that fast leaves almost no chance," he says.
In a shooting war, Singh says, the legal position is blunt.
Fighting between the United States and Iran had been under way since 28 February, with claims that 17 Iranian naval vessels had already been destroyed.
"When a shooting war is on, any ship of a belligerent country becomes fair game," he says.
Many questions remain. Why was the Iranian warship still in waters near Sri Lanka nearly two weeks after leaving India's naval exercise? Was it heading home, or on another mission? And how long had the US submarine been tracking it before firing?
For Delhi, the episode is diplomatically awkward.
India has drawn closer to Washington on defence while maintaining long-standing political and economic ties with Tehran - a balancing act the war has made harder.
Indian Prime Minister Narendra Modi has called broadly for "dialogue and diplomacy" to resolve conflicts, but has neither addressed the sinking of the Iranian vessel directly nor criticised the American strike.
Iran's Foreign Minister Abbas Araghchi described the attack as "an atrocity at sea" and stressed that the frigate had been "a guest of India's Navy". Meanwhile Sri Lanka has taken control of another Iranian naval vessel off its coast after an engine failure forced it to seek port, a day after the US attack.
The episode has nonetheless sparked debate within India's strategic community.
Kanwal Sibal, a veteran diplomat, argued that India's responsibility may not be legal, but it is moral.
"The Iranian ship would not have been where it was had India not invited it to the Milan exercise," he wrote on X. "A word of condolence at the loss of lives of those who were our invitees would be in order."
Others like Chellaney have framed the issue in more strategic terms.
He described the strike as a blow to India's maritime diplomacy. The torpedoing of the frigate in "India's maritime backyard", he argued, punctured Delhi's carefully cultivated image as a "preferred security partner" in the Indian Ocean.
"In one torpedo strike, American hard power has punctured India's carefully cultivated soft power," says Chellaney.
As the debate gathered pace in strategic circles, India's official response remained cautious.
External Affairs Minister S Jaishankar said on X that he had held a telephone conversation with Araghchi, and also posted a photograph of a meeting with Iran's Deputy Foreign Minister Saeed Khatibzadeh at a foreign policy summit in Delhi.
For military historian Srinath Raghavan, the legal position is clear: once the Iranian vessel left India's shores, Delhi had no formal responsibility.
The strategic message, however, is harder to ignore.
"First, the spreading geography of this war. Second, India's limited ability to manage its fallout," says Raghavan.
"Indeed, the US Navy has fired a shot across the bow aimed at all regional players, including India."
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