Iranian Navy frigate IRIS Dena sinks near Sri Lanka after possible submarine attack.

On March 4, 2026, the Iranian Navy frigate IRIS Dena sank south of Sri Lanka after issuing a distress call at dawn, potentially after being attacked by a submarine.

Sri Lanka's Foreign Minister Vijitha Herath says that the Iranian Navy frigate IRIS Dena sank about 40 km south of Sri Lankan coasts, near Galle, after issuing a distress call early on March 4, 2026. Sri Lankan naval and air units launched a rescue operation and recovered wounded sailors. Officials indicated a possible submarine attack while search operations continued for the missing crew.
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IRIS Dena, pennant number 75, belonged to the Iranian Navy’s Southern Fleet and was built at Iranian Navy factories in Bandar Abbas, laid down in 2012, launched in 2015, and commissioned into service in 2021. (Picture source: Iranian MoD)

On March 4, 2026, Sri Lanka's Foreign Minister Vijitha Herath announced that the Iranian Navy frigate IRIS Dena sank south of Sri Lanka after issuing a distress call at dawn, prompting a rescue operation by Sri Lankan naval and air assets that recovered 32 critically wounded sailors. Sri Lankan naval and defence officials suggested the possibility of a submarine attack to Reuters, though the origin of any such attack remained officially unclear. The vessel went down about 40 kilometres south of the island near Galle, just outside Sri Lanka’s territorial waters in the Indian Ocean.

The frigate carried a crew of about 180 sailors when the emergency unfolded, and authorities confirmed that the rescued personnel were transported to a hospital in southern Sri Lanka. Sri Lankan forces deployed two navy vessels and an aircraft to the area to assist the ship and evacuate survivors from the water. Police reinforced security around the hospital in Galle, located about 115 kilometres south of Colombo, as the injured sailors arrived. Sri Lanka’s response began after the distress call was received early in the morning as the frigate reported that it was sinking outside the island’s territorial waters. Two Sri Lankan navy ships and an aircraft were sent to the location, and the Sri Lankan Air Force also participated in the rescue effort.

The rescued sailors were transferred to the main hospital in Galle while search operations continued in the surrounding waters for the remaining members of the crew. Authorities confirmed that the response was carried out within Sri Lanka’s designated search and rescue area in the Indian Ocean and under international maritime obligations to assist vessels in distress. Officials indicated that the fate of the rest of the crew remained unknown while the search operation continued. During a parliamentary debate, an opposition legislator asked whether the vessel had been bombed in connection with ongoing US-Israeli attacks against Iran, but the government did not provide a response at the time of writing.

Before the sinking, IRIS Dena had participated in the International Fleet Review 2026 held in Visakhapatnam, India, which brought together naval forces from multiple countries for a large gathering of warships and maritime activities. The frigate arrived in the Indian port city in February 2026 to join the fleet review events and associated naval engagements. After the main fleet review ceremony on February 18, 2026, the ship docked in Visakhapatnam on February 20, 2026. Iran’s naval commander Commodore Shahram Irani was present in India during the events and met India’s Chief of the Naval Staff Admiral Dinesh K Tripathi during the visit. The Iranian naval delegation attended several activities connected to the fleet review. These engagements formed part of a wider set of naval events hosted by India during the same period.

MILAN 2026 was conducted alongside the International Fleet Review and involved multinational naval cooperation activities that combined harbor events with a sea phase of joint exercises. IRIS Dena participated in the exercise as part of the Iranian naval presence in Visakhapatnam during February 2026. The activities included exchanges between naval personnel and coordinated maritime drills involving participating navies. Iran’s naval commander traveled to India to attend the exercise, the fleet review, and the Indian Ocean Naval Symposium. A US Navy destroyer, USS Pinckney, had been scheduled to participate in the fleet review and MILAN exercise, but did not attend because of emergent operational requirements. A US Navy P-8 maritime patrol aircraft instead took part in the engagements, and USS Pinckney had departed Singapore on February 11, 2026 after undergoing repairs.

IRIS Dena, pennant number 75, belonged to the Iranian Navy’s Southern Fleet and was named after Mount Dena. The ship was built at Iranian Navy factories in Bandar Abbas, laid down in 2012, launched in 2015, and commissioned into service in 2021. The frigate measured about 95 metres in length with a beam of about 11.1 metres and an estimated draught of 3.25 metres. Displacement reached about 1,500 tonnes. The propulsion system included four diesel engines rated at 5,000 horsepower each, supported by diesel generators, enabling a maximum speed of about 30 knots. Aviation facilities included a helipad capable of operating a Bell 212 anti-submarine warfare helicopter.

The frigate carried an Asr three-dimensional PESA radar and electronic warfare equipment. Its armament included a 76 mm dual-purpose rapid fire naval gun and a Fath 40 mm anti-aircraft cannon derived from the Bofors design. Additional weapons included crew-served 20 mm Oerlikon cannons and launchers for anti-ship missiles such as the C-802 or Noor series. Surface-to-air missiles identified as Sayad-2 were installed for air defense. Anti-submarine warfare capabilities included two triple 324 mm light torpedo launchers. Defensive countermeasures included chaff dispensers. The radar system could track multiple targets and engage several simultaneously with a coverage range extending to about 300 kilometres.

The Moudge-class is a series of domestically produced Iranian frigates developed for the Iranian Navy. Ships in the class typically displace about 1,500 tonnes and measure about 95 metres in length with a beam of about 11.1 metres and a draught of about 3.25 metres. The propulsion arrangement includes engines delivering about 20,000 horsepower combined with diesel generators and a top speed of about 30 knots. Sensors include the Asr three-dimensional long-range radar. The class also integrates electronic warfare systems and decoy launchers. Aviation facilities include a landing pad capable of supporting a Bell 214 anti-submarine warfare helicopter.

Weapons fitted to Moudge class frigates include a 76 mm Fajr-27 naval gun and either a 40 mm Fath-40 anti-aircraft cannon or a 30 mm Kamand close-in weapon system. Additional weapons include 20 mm cannons and 12.7 mm heavy machine guns. Surface-to-air missiles such as Mehrab and Sayyad variants are installed for air defense. Anti-ship missile armament includes Noor or Qader missiles, sometimes in sets of four or eight launchers, depending on the ship. Anti-submarine warfare capability is provided by triple 324 mm torpedo tubes. Chaff launchers and electronic warfare systems support defensive countermeasures. These ships were developed to replace older vessels such as the Alvand class in Iranian service.

The first ships of the Moudge class began construction in the early 2000s, and several vessels were subsequently launched including Jamaran, Damavand, Sahand, and Dena. Jamaran entered service at Bandar Abbas while other ships were built at facilities associated with the Iranian Navy and the Marine Industries Organization. The frigate Damavand ran aground on a concrete breakwater near Bandar-Anzali on January 10, 2018, during severe weather conditions. The class has continued to expand as part of Iran’s domestic naval construction program. These ships form a component of the Iranian surface fleet operating in the Persian Gulf, the Arabian Sea, and the Indian Ocean.

Iran has employed Moudge class frigates for maritime patrols, escort missions, and long-distance naval deployments beyond its immediate region. The frigate IRIS Dena and the support vessel IRIS Makran completed a long-distance mission between 2022 and 2023 that circumnavigated the globe and covered more than 65,000 kilometres of sea routes. The voyage included port visits in locations such as Jakarta, Rio de Janeiro, and Cape Town before the ships returned to Bandar Abbas after about eight months at sea. Participation in international naval gatherings such as the International Fleet Review 2026 and the MILAN exercise illustrated the use of these frigates for operational presence and diplomatic naval engagement. The sinking of IRIS Dena occurred shortly after the ship had completed these activities and departed India during its return voyage.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.