A U.S. Navy submarine fired a torpedo that sank an Iranian warship in the Indian Ocean on Tuesday night, Defense Secretary Pete Hegseth announced Wednesday, marking the first sinking of an enemy combatant vessel by an American submarine since World War II and dramatically widening the naval dimension of the ongoing U.S.-Israel campaign against Iran.

The ship at the launch ceremony in 2021
The ship at the launch ceremony in 2021

Hegseth, speaking at a Pentagon briefing, described the strike as targeting "an Iranian warship that thought it was safe in international waters." He said the vessel was hit with a single torpedo, resulting in a "quiet death" for the ship. "Instead, it was sunk by a torpedo," Hegseth stated, emphasizing the precision and reach of U.S. forces. The Pentagon released declassified footage showing the underwater explosion and the ship's rapid sinking, though details on the specific submarine or torpedo model remained classified.

The targeted vessel was identified as the IRIS Dena, a Moudge-class frigate of the Iranian Navy's Southern Fleet. The ship, with a crew of approximately 180, had been returning to Iran after participating in the MILAN 2026 multinational naval exercise in Visakhapatnam, India. Sri Lankan authorities reported the frigate issued a distress call early Wednesday off the southern coast near Galle. The Sri Lankan navy rescued 32 survivors, many seriously injured, and transported them to local hospitals. Reports varied on casualties: Sri Lankan officials cited around 140 missing, while Reuters and other sources reported at least 80 killed, with dozens wounded. Iranian state media has not yet confirmed the loss or casualty figures.

The incident occurred in international waters in the Indian Ocean, far from the Persian Gulf theater where most naval engagements have unfolded since the conflict began Feb. 28, 2026. U.S. officials framed the strike as part of broader efforts to neutralize Iran's naval capabilities and prevent retaliatory attacks on international shipping or allied forces. Hegseth declared the Iranian navy "ineffective, decimated, destroyed," adding that it "rests at the bottom of the Persian Gulf" after earlier U.S. strikes sank multiple vessels, including frigates like Jamaran-class ships and the drone carrier Shahid Bagheri.

The sinking represents a significant escalation. It is the first U.S. submarine torpedo kill against an enemy warship in 81 years, last occurring during World War II against Japanese and German vessels. The attack extends U.S. operations beyond the Middle East, targeting Iranian assets in distant waters amid Iran's attempts to project power and disrupt global trade routes.

The conflict, now in its sixth day, has seen intense joint U.S.-Israeli airstrikes on Iranian military infrastructure, missile sites, command centers, and symbols of regime power in Tehran and elsewhere. Iran has responded with missile and drone barrages targeting U.S. bases in Qatar, Bahrain, Kuwait, and the UAE, as well as Israel and allies. Tehran has vowed to destroy regional military and economic infrastructure, while disrupting shipping through the Strait of Hormuz with threats, drone attacks, and unmanned surface vessels.

U.S. Central Command reported sinking 17 Iranian vessels overall, including corvettes, frigates, and support ships, in the Gulf of Oman and Persian Gulf since operations began. President Donald Trump announced "major combat operations" on Feb. 28, with more than 1,000 targets struck in the opening days. The campaign aims to degrade Iran's retaliatory capabilities, including ballistic missiles and naval forces.

Sri Lanka's foreign minister confirmed the rescue operation but provided no comment on responsibility for the sinking. Maritime security sources noted the area sees regular Iranian naval transits, but the strike's location surprised analysts given its distance from primary conflict zones.

The incident has intensified global concerns over oil supply routes and shipping safety. Oil prices remained elevated Wednesday, with Brent crude near $84 per barrel amid fears of further disruptions. Markets reacted to the widening naval theater, though some analysts viewed the strike as targeted rather than a prelude to broader Indian Ocean operations.

Iran has not issued an official response to the sinking as of Wednesday afternoon, but state media focused on domestic resilience and vows of retaliation. The loss of the IRIS Dena, a relatively modern frigate equipped for anti-ship and air defense roles, further weakens Iran's surface fleet, already battered by strikes on bases like Bandar Abbas.

Hegseth's announcement underscored U.S. resolve. "The Iranian navy is no more," he said, framing the action as evidence of America's ability to project power globally. No U.S. casualties were reported in the operation.

As the war expands, focus remains on containing escalation while degrading Iran's offensive tools. Diplomatic channels, including indirect contacts, continue amid calls for de-escalation, but both sides show no immediate signs of backing down.

The sinking of the IRIS Dena highlights the conflict's naval reach and the risks to Iranian forces operating far from home waters. Rescue efforts by Sri Lanka continue, with hopes fading for additional survivors as search operations persist.