Sinking of IRIS Dena

During the 2026 Iran war, the Iranian Navy frigate IRIS Dena was torpedoed and sunk by the United States Navy's Los Angeles-class submarine USS Charlotte in the Indian Ocean. A week prior to the attack Dena concluded it's participation in the International Fleet Review 2026, a naval exercise hosted by India, and was returning to home when it was attacked and sunk in international waters approximately 19 nautical miles (35 km; 22 mi) off the coast of Sri Lanka. On 4 March, Charlotte fired two Mark 48 torpedoes at Dena, which struck the frigate and caused its sinking. According to some reports, the vessel, owing to its participation in the international exercise, was not carrying operational armaments at the time. Also, the vessel's Bell 212 helicopter was not present during the incident. At the time of the attack Dena had a crew of 136 personnel; 104 were reported killed and 32 survived. It was further reported that the remains of 20 of the deceased were not recovered.

The sinking occurred amid heightened hostilities involving 2026 Iran war. It has been described as the only instance since the Pacific War of World War II in which a United States Navy submarine sank a surface vessel using torpedoes, and the first ever known torpedo kill on an enemy vessel by an American nuclear submarine. More broadly, it was the first sinking of an enemy surface ship by a nuclear-powered submarine since the sinking of ARA General Belgrano by the Royal Navy submarine HMS Conqueror during the Falklands War.

The attack is the subject of controversy and claims that it constituted a war crime related to whether an unarmed warship is a lawful target, the legality of the war in general, and whether or to what extent the submarine had an obligation to assist or ensure assistance to the shipwrecked crew under the Second Geneva Convention.