The Iranian frigate IRIS Dena became the focus of international attention after sinking on March 4, 2026, in the Indian Ocean, approximately 40 nautical miles off the southern coast of Sri Lanka. Hours after the incident, U.S. Officials confirmed that the ship had been attacked and sunk by a U.S. Navy submarine, amid a regional conflict involving Iran.
The vessel, officially identified as IRIS Dena 75, was part of the Southern Fleet of the Islamic Republic of Iran Navy and was named after Mount Dena.
The Dena belonged to the Moudge class, a series of frigates developed by Iran based on previous designs, though it has been described as both a frigate and a destroyer in English-language media. In Persian, the term used is “navshekan,” which translates to destroyer.
Estimated to displace between 1,300 and 1,500 tons, the ship measured 94 meters in length and 11 meters in beam. It featured a helicopter platform, expanding its operational capabilities for surveillance and deployment missions.
One of its distinguishing features was its propulsion system: it was the first Iranian destroyer equipped with four domestically produced “Bonyan 4” engines, each with a power of 5,000 horsepower, giving it a total power of 20,000 hp. It also had a transverse thruster system in the bow to improve maneuverability in complex operations.
According to Iranian naval authorities, the Dena incorporated significant improvements over other units in its class. It was equipped with a vertical launch system (VLS), a strategically important capability that allowed it to fire missiles more quickly and versatilely.
Its arsenal included Qader anti-ship missiles, surface-to-air missiles, a 76 mm Fajr-27 naval gun, a 40 mm Fath-40 anti-aircraft system, two 20 mm Oerlikon guns, heavy 12.7 mm machine guns, and triple 533 mm torpedo launchers.
For detection, it incorporated an Asr radar with 360-degree coverage and an approximate range of 300 kilometers. Its fire control system, according to official information, could track up to 40 targets and engage five simultaneously.
Prior to its sinking, the Dena had participated in long-range missions. Along with the logistics ship IRIS Makran, it was part of the 86th Iranian naval flotilla that carried out a “360 degrees” global circumnavigation mission considered historic by Tehran.
During the voyage, it visited Brazil, which caused concern from the U.S. Government.
U.S. Ambassador Elizabeth Bagley previously urged Brazil not to allow the ships to dock. “In the past, these ships have facilitated illegal trade and terrorist activities, and have also been sanctioned by the United States. Brazil is a sovereign nation, but we firmly believe that these ships should not dock anywhere,” she stated.
“We continue to monitor Iran’s attempts to have a military presence in the Western Hemisphere,” a Department of State spokesperson told Fox News in January.
In February 2026, the Dena participated in the International Naval Review held in Visakhapatnam, India, where it also participated in the Indian Ocean Naval Symposium and MILAN 2026 exercise. Following the event, the commander of the Iranian Navy held official meetings with Indian naval authorities.
On March 4th, amid escalating conflict with Iran, the Dena issued a distress signal when it was approximately 40 nautical miles off the port of Galle, in southern Sri Lanka. The Sri Lankan Navy deployed two vessels and an aircraft to assist the crew, fulfilling its international search and rescue obligations in its area of responsibility.
At least 180 crew members were on board at the time of the incident. Dozens of sailors were rescued and transported to Karapitiya University Hospital, while more than a hundred remained missing in the hours following the sinking. Local authorities also confirmed the recovery of some bodies and indicated that crew members had reported an explosion before the ship went down.
That same day, U.S. Officials confirmed that the ship had been sunk by a U.S. Navy submarine in international waters.
Frequently Asked Questions
What type of ship was the IRIS Dena?
The IRIS Dena was a Moudge-class frigate, though it has also been described as a destroyer. It was part of the Southern Fleet of the Islamic Republic of Iran Navy.
Where did the sinking of the IRIS Dena occur?
The IRIS Dena sank in the Indian Ocean, approximately 40 nautical miles off the southern coast of Sri Lanka.
How many crew members were on board the IRIS Dena at the time of the incident?
At least 180 crew members were on board the IRIS Dena when it sank. Dozens were rescued, but more than a hundred remained missing in the hours following the incident.
As the situation unfolds, what impact might this event have on regional stability and international relations?
