The Most Chilling Detail in the U.S. Attack on an Iranian Naval Ship

The U.S. Navy’s attack on an Iranian frigate, the IRIS Dena, on Wednesday was the first time an American submarine has sunk an enemy ship since World War II. But the Dena may not have been armed because it was returning from an international exercise in the Indian Ocean, and the U.S. Navy likely knew it because it was taking part in the same exercise. 

Both the United States and Iran were taking part in the MILAN 2026 exercise, organized by the Indian Navy, on February 15–26, with the U.S. sending a maritime patrol aircraft and Iran sending the Dena. Iranian sailors from the ship paraded on land before India’s president.

Contingent from #IRISDena marching in Vishakhapatnam during #Milan-2026 naval exercise on 19th February. IRIS Dena sunk this morning near #Galle, Srilanka by USA submarine, fourth such kill after WW2. War reaches in #IndianOcean . #IranIsraelWar #IranWar #IndianNavy pic.twitter.com/skDCJlbaAp

— Krishna Mohan Mishra (@kmmishratv) March 4, 2026

The exercise in question required ships not to carry any ammunition. Normally, the Dena carries various missiles and guns, including anti-ship missiles. Because the U.S. also took part, it would have been aware that the Dena was unarmed. Former Indian Foreign Minister Kanwal Sibal accused the attack of being “premeditated as the US was aware of the Iranian ship’s presence in the exercise.” 

“The US has ignored India’s sensitivities as the ship was in these waters because of India’s invitation,” Sibal said in a post on X. The Iranian ambassador to India, Mohammad Fathali, condemned the attack and said the ship was unarmed. 

“We will respond to this assassination very strongly. This ship was unarmed and in a regular maneuver at sea. I think that the United States and the Zionist regime want to disturb and destroy all the international law and international norms,” Fathali said. 

At least 87 sailors were killed in the torpedo attack in international waters in the Indian Ocean, and the Sri Lankan navy responded to the Dena’s distress call and rescued 32 survivors, but 61 members of the crew are still missing. The U.S. didn’t respond to the call, and Secretary of Defense Pete Hegseth crowed about the attack to reporters on Wednesday. 

“An American submarine sunk an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo,” Hegseth said, calling it a “quiet death.” As a result of the attack, an Iranian supply tanker that was also near Sri Lanka, the IRIS Bushehr, has taken refuge in the island country.  

The sinking of the Dena seems to be part of Hegseth’s new policy of ignoring “stupid rules of engagement” and “punching them while they’re down,” and it raises questions of what the Trump administration would say if a country like Iran attacked an American ship it knew was unarmed.