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A US submarine has torpedoed the Iranian frigate, Islamic Republic of Iran Ship ‘Dena’, off the southern coast of Sri Lanka in the Indian Ocean, marking the first American submarine kill with a torpedo since World War II.
The frigate was reportedly heading back to Iran from an eastern Indian port after attending an Indian-organised naval exercise, Milan, in the Bay of Bengal from February 18 to 25.
Search-and-rescue operation were launched by Sri Lankan authorities with around 120 people rescued from the sinking vessel. Around 60 people were unaccounted for.
https://t.co/PiqQpVIrMu pic.twitter.com/Wc1e0B0um7
— Department of War 🇺🇸 (@DeptofWar) March 4, 2026
“In the Indian Ocean an American submarine sunk an Iranian warship that thought it was safe in international waters,” according to a statement from US Defense Secretary Pete Hegseth speaking at the Pentagon.
“Instead, it was sunk by a (Mark 48) torpedo. Quiet death.
“The first sinking of an enemy ship by a torpedo since World War 2. Like in that war, back when we were still the War Department, we are fighting to win."
.@SECWAR “In the Indian Ocean—an American submarine sunk an Iranian warship, that thought it was safe in international waters.
— DOW Rapid Response (@DOWResponse) March 4, 2026
Instead, it was sunk by a torpedo—Quiet Death.
The first sinking of an enemy ship by a torpedo since World War 2. Like in that war—back when we were… pic.twitter.com/Y97YQBxQza
Australian maritime expert, UWA Defence and Security Institute Adjunct Professor and former Royal Australian Navy officer Jennifer Parker said the attack is considered to be a significant development.
“In an war, once commenced, such vessels are lawful targets under the Law of Armed Conflict, and the United States has been clear that destroying the Iranian Navy forms part of its military objectives. (It) sends a powerful signal.”
“There should be no sympathy for the Iranian regime. But sailors are sailors. Regardless of the politics, there should always be sympathy for those lost at sea. For those recovered, I wish them a speedy recovery. Credit to Sri Lanka for the rescue effort.”
“A declaration of war is not needed for an international armed conflict to exist. The existence of an IAC, means the LONW applies. An Iranian warship under the LONW (law of naval warfare) is a belligerent and therefore a lawful target," Parker added.
“With respect to rescue, any vessel coming across survivors has a requirement to rescue them. However, a submarine does not have that capability.
“It is notable this was done near Sri Lankan territorial waters which allowed for a Sri Lankan rescue.
“Re AO (Administrative Arrangements Orders), under LONW international waters is a lawful area to engage belligerents. There is no requirement to constrain it to the ME.
