An Iranian naval vessel was sunk in the Indian Ocean after being struck by a torpedo launched from a US submarine, an incident that reportedly killed at least 80 sailors, according to reports cited by Reuters.

The ship, identified as IRIS Dena, belonged to Iran’s navy and had recently participated in a multinational naval drill hosted by India. The frigate had earlier sailed to India for the MILAN 2026, where several global navies conducted joint maritime training and operational exercises.

The vessel had also taken part in a previous edition of the same drill in 2024 before departing the region shortly before the attack occurred.

US officials have not publicly confirmed the exact casualty figure, but the strike itself was acknowledged by Pete Hegseth. Speaking to reporters, he described the attack as proof of the United States’ operational reach during the ongoing conflict with Iran.

According to him, the Iranian ship believed it was operating safely in international waters before being destroyed by a torpedo fired from the American submarine.

The United States Department of Defense also released monochrome footage that appeared to show a submarine periscope view followed by an explosion at sea. Military analysts noted that releasing near real-time visuals of a submarine strike is extremely rare, highlighting how modern conflicts increasingly involve rapid information sharing alongside battlefield operations.

Experts believe the Iranian vessel may not have detected the approaching submarine, even when it was operating near periscope depth, suggesting a significant tactical advantage for the attacking vessel.

The Indian Navy had earlier stated that MILAN 2026—one of the largest naval drills in the Indo-Pacific—brought together numerous countries to improve coordination, maritime surveillance and joint operational capabilities. The exercise included harbour and sea phases focusing on complex missions such as anti-submarine warfare, air defence and search-and-rescue operations.

It remains unclear whether the US submarine had been monitoring the Iranian frigate during its journey to and from the exercise. Some defence observers speculate that the vessel could have been under surveillance for intelligence purposes throughout its deployment.

Authorities in Sri Lanka said rescue teams recovered 32 crew members from the water following the incident, while 148 sailors remain unaccounted for, raising fears that the death toll could climb further.

Hegseth described the attack as a “quiet death,” noting it was the first time since World War II that the United States had destroyed an enemy warship using a torpedo launched from a submarine.

The Pentagon has indicated that weakening Iran’s naval capabilities is one of the objectives of the ongoing US-Israel military campaign against Tehran.