‘Quiet death’: US submarine sinks Iranian warship IRIS Dena in Indian Ocean, first torpedo kill since WWII

A United States Navy fast-attack submarine sank the Iranian Navy frigate IRIS Dena in the Indian Ocean on Tuesday, March 3, 2026, using a single Mark 48 heavyweight torpedo fired while the Iranian warship transited international waters south of Sri Lanka. The United States Department of Defense confirmed the strike on Wednesday, March 4, 2026, during a Pentagon press briefing dedicated to Operation Epic Fury, the joint American-Israeli military campaign against Iran. United States Defense Secretary Pete Hegseth confirmed the attack alongside Chairman of the Joint Chiefs of Staff General Dan Caine, describing it as the first sinking of an enemy ship by a United States submarine since World War II, a span of more than 80 years.

The IRIS Dena, a Moudge-class frigate assigned to the Southern Fleet of the Islamic Republic of Iran Navy, was in the Indian Ocean after completing its participation in the Milan 2026 multinational naval exercise and fleet review held in Visakhapatnam, on India’s eastern coast, which concluded on February 25, 2026. The vessel was returning westward toward Iranian home waters when it was struck. The 1,500-ton warship was armed with Qader anti-ship missiles, Sayyad surface-to-air missiles, a 76 millimeter main gun, an array of lighter caliber weapons, lightweight torpedoes, and a 3D phased array radar system, and was configured to carry a helicopter. The IRIS Dena was among the most capable and modern surface combatants in the Islamic Republic of Iran Navy’s Southern Fleet, and had represented Iran on an international port call tour in 2023.

The IRIS Dena issued a distress call between 6:00 AM and 7:00 AM local Sri Lankan time on Wednesday, March 4, 2026. Within less than one hour, a Sri Lankan Navy rescue vessel reached the area approximately 40 kilometres south of the southern port city of Galle. When the rescue crew arrived on scene, the frigate had already sunk completely, leaving only an oil slick on the surface. Sri Lankan Navy spokesman Commander Buddhika Sampath stated that Sri Lanka dispatched rescue vessels and aircraft under its international maritime obligations, as the location of the sinking fell within Sri Lanka’s designated search and rescue area in the Indian Ocean.

Sri Lankan Foreign Minister Vijitha Herath informed parliament that 180 crew members were aboard the IRIS Dena at the time of the torpedo strike. Sri Lankan Navy and naval air units rescued 32 survivors, all of whom were transported under medical care to the main hospital in Galle, approximately 115 kilometres south of Colombo. Sri Lanka’s deputy foreign minister stated on local television that at least 80 Iranian sailors had been killed. With the search and rescue operation still active as of Wednesday afternoon, approximately 148 crew members remained unaccounted for. Commander Sampath confirmed that bodies believed to be those of IRIS Dena crew members had been recovered from surrounding waters during the operation. Sri Lanka’s navy and air force declined to release footage from the rescue, citing the involvement of the military of another state.

What is Operation Epic Fury and why did the United States Navy target the Iranian frigate IRIS Dena in the Indian Ocean during the joint US-Israel campaign against Iran?

Operation Epic Fury is the joint United States-Israeli military campaign launched on February 28, 2026, following a strike that killed Iranian Supreme Leader Ali Khamenei and numerous senior Iranian military and government officials. The campaign has targeted Iranian air defense infrastructure, ballistic missile systems, naval assets, and military installations. General Caine confirmed at the Pentagon briefing on March 4, 2026, that the United States military had struck more than 2,000 targets across Iran and destroyed more than 20 Iranian naval vessels, including one Iranian submarine, since the start of Operation Epic Fury.

The sinking of the IRIS Dena represented a significant geographic expansion of Operation Epic Fury. The strike was the first action of the campaign to occur in the area of responsibility of the United States 7th Fleet, extending military operations well beyond the Persian Gulf and the Gulf of Oman and into the broader Indo-Pacific. General Caine stated during the briefing that the United States military had, at that point, effectively neutralized Iran’s major naval presence in the region, and that strike operations on Iranian infrastructure and naval capability would continue over the following 24 to 48 hours. United States Central Command commander Admiral Brad Cooper stated that as of Tuesday, March 3, 2026, not a single Iranian ship remained underway in the Arabian Gulf, the Strait of Hormuz, or the Gulf of Oman.

Other Iranian naval vessels destroyed during Operation Epic Fury included the Soleimani-class missile catamaran corvette IRIS Shahid Sayyad Shirazi, the drone carrier IRIS Shahid Bagheri, and the forward base and replenishment ship IRIS Makran. Defense Secretary Hegseth also confirmed at the March 4 briefing that a vessel named the Soleimani, an Iranian warship named after the late Islamic Revolutionary Guard Corps Quds Force commander Qasem Soleimani, had been sunk on the night of March 3. Qasem Soleimani was killed in a United States drone strike at Baghdad International Airport in January 2020, during President Donald Trump’s first term.

Why is the torpedo sinking of IRIS Dena a historically significant milestone for United States Navy submarine operations and global naval warfare?

The destruction of the IRIS Dena by a Mark 48 torpedo is the first confirmed sinking of an enemy surface warship by a United States Navy submarine since the conclusion of World War II in 1945. The last comparable event involving any nation’s submarine took place on May 2, 1982, when the Royal Navy nuclear-powered attack submarine HMS Conqueror sank the Argentine Navy light cruiser ARA General Belgrano during the Falklands War in the South Atlantic. That attack, and the loss of the IRIS Dena, are now the only two instances of submarine torpedo kills against surface warships since the end of World War II.

The Mark 48 is a heavyweight, guided anti-ship and anti-submarine torpedo whose warhead is designed to detonate beneath a target vessel’s hull, generating a pressure wave strong enough to lift and buckle the ship’s keel, causing rapid and catastrophic structural failure. Pentagon-released infrared periscope footage recorded through the attacking submarine’s optronics mast showed the detonation occurring beneath the stern of the IRIS Dena, visibly lifting the vessel before it began to sink. The identity of the United States Navy fast-attack submarine that fired the torpedo was not disclosed, consistent with standard operational security protocols for submarine operations.

General Caine characterized the strike as a demonstration of the United States military’s unique global reach. The IRIS Dena was operating far beyond its home region in the Indian Ocean at the time of the attack, having most recently participated in naval exercises off the eastern coast of India. The ability to locate, track, and destroy an Iranian naval vessel deployed thousands of kilometres from the Persian Gulf underscored the extended operational range of United States Navy submarine forces.

How did Iran’s threatened closure of the Strait of Hormuz contribute to the United States military campaign targeting the Islamic Republic of Iran Navy during Operation Epic Fury?

Iran announced the effective closure of the Strait of Hormuz to international shipping as a retaliatory measure against the United States-Israeli military campaign. The Strait of Hormuz is the world’s most strategically critical maritime chokepoint for energy transit, with approximately 21 million barrels of petroleum products passing through it daily, representing roughly one-fifth of total global oil supply. Iran stated it would attack and destroy any vessel attempting to transit the strait, generating immediate concern across global energy markets, shipping companies, and oil-importing nations.

In direct response to the Iranian Strait of Hormuz closure threat, President Trump directed the United States International Development Finance Corporation to immediately provide war risk insurance to shipping companies for energy cargoes transiting the Persian Gulf at commercially accessible rates. President Trump also stated publicly that the United States Navy would escort oil tankers through the Strait of Hormuz as required to ensure uninterrupted energy transit. The systematic targeting and destruction of the Islamic Republic of Iran Navy, including vessels in the Arabian Gulf, the Gulf of Oman, and, as demonstrated by the IRIS Dena strike, the wider Indian Ocean, was directly linked to the objective of denying Iran the naval capability to enforce its Strait of Hormuz closure declaration.

Hegseth told reporters at the March 4 Pentagon briefing that the Islamic Republic of Iran Navy was “combat ineffective, decimated, destroyed, defeated,” and that Iran’s navy was, in his characterization, “no more.” The destruction of the IRIS Dena, the furthest-range strike against an Iranian naval asset since the start of Operation Epic Fury, reinforced the United States position that Iranian naval forces would not be permitted to operate anywhere in the region without risk of engagement.

What does the sinking of the Iranian frigate IRIS Dena mean for Iran, the United States, Sri Lanka, and global naval and maritime security?

• A United States Navy fast-attack submarine sank the Iranian Navy Moudge-class frigate IRIS Dena approximately 40 kilometres south of Galle, Sri Lanka, on March 3, 2026, using a single Mark 48 heavyweight torpedo fired in international waters during Operation Epic Fury.
• The strike marked the first confirmed sinking of an enemy warship by a United States Navy submarine since World War II, and the first submarine torpedo kill of a surface vessel anywhere in the world since HMS Conqueror sank ARA General Belgrano during the 1982 Falklands War.
• The Islamic Republic of Iran Navy frigate IRIS Dena carried 180 crew members at the time of the attack. Sri Lanka rescued 32 survivors. At least 80 Iranian sailors were reported dead, and approximately 148 crew members remained missing as search and rescue operations continued.
• General Caine stated that the United States military had destroyed more than 20 Iranian naval vessels and an Iranian submarine since Operation Epic Fury began on February 28, 2026, and that Iran’s major naval presence in the region had been effectively neutralized.
• The sinking of the IRIS Dena extended Operation Epic Fury geographically into the United States 7th Fleet area of responsibility for the first time, demonstrating United States Navy submarine capability to locate and engage Iranian naval assets operating far outside the Persian Gulf region.