80 feared dead after US submarine sinks Iranian warship near Sri Lanka

At least 80 people are feared dead after a United States submarine sank an Iranian naval warship in the Indian Ocean, according to reports citing officials and defence sources, marking one of the most dramatic naval engagements in the escalating US-Iran conflict.

The vessel, IRIS Dena, a Moudge-class frigate of the Iranian navy, reportedly went down near Sri Lanka after being struck by a torpedo fired from a US submarine. The warship had recently participated in MILAN 2026, a major multinational naval exercise hosted by India, before beginning its return journey when the attack occurred.

Sri Lankan authorities said rescue teams had recovered 32 injured crew members from the sea, while 148 sailors remained missing, raising fears that the death toll could rise further.

The United States has not confirmed casualty figures but acknowledged carrying out the strike. US defence secretary Pete Hegseth confirmed that an American submarine had targeted and sunk the Iranian vessel.

“An American submarine sunk an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo,” Hegseth told reporters, describing the attack as evidence of Washington’s global military reach.

He characterised the strike as a “quiet death” and said it marked the first time since World War II that a US submarine had sunk an enemy warship using a torpedo.

The US Department of Defense also released a short black-and-white video purportedly showing footage from a submarine periscope, with a distant explosion visible in the frame. Military analysts said the release of what appeared to be near real-time visuals of a submarine attack is extremely rare, underscoring how the conduct of modern warfare — and the communication surrounding it — has evolved.

According to defence observers, the Iranian frigate likely did not detect the American submarine before the strike, even if the US vessel had been operating at periscope depth. Analysts say this suggests a significant tactical advantage in stealth and tracking capabilities.

IRIS Dena had earlier taken part in MILAN 2026, one of the largest multilateral naval exercises in the Indo-Pacific region. In a statement issued ahead of the exercise in February, the Indian Navy said the drills were aimed at strengthening maritime cooperation, interoperability and collective response capabilities among participating navies.

The exercise included both harbour and sea phases and involved complex maritime operations such as anti-submarine warfare, air defence, search-and-rescue missions and coordinated naval manoeuvres.

It remains unclear whether the US submarine had been monitoring the Iranian warship during its journey to and from India. However, defence analysts said it is common practice for naval forces to passively track foreign warships for intelligence gathering and operational awareness.

Some experts have speculated that the US submarine may have been shadowing the Iranian vessel throughout its voyage from Iran to India for the naval drills.

The sinking comes amid intensifying hostilities between Washington and Tehran. According to the Pentagon, a central objective of the ongoing US-Israeli military campaign against Iran — launched earlier this week — is to significantly degrade Iran’s naval capabilities.

With agency inputs