Washington/Colombo/Tehran, March 5, 2026 – A United States Navy attack submarine has sunk the Iranian Navy frigate IRIS Dena in the Indian Ocean using a single Mark 48 torpedo, U.S. Defense Secretary Pete Hegseth confirmed on Wednesday. The strike, which occurred in international waters approximately 40 nautical miles (74 km) off the southern coast of Sri Lanka near Galle, marks the first time a U.S. submarine has sunk an enemy surface vessel with a torpedo in combat since World War II.
The attack took place early on March 4, 2026, local time, as the IRIS Dena—a Moudge-class frigate assigned to Iran's Southern Fleet—was returning to Iran after participating in multinational naval exercises hosted by India in the Bay of Bengal. The vessel issued a distress call around 5:08 a.m. Sri Lanka Standard Time reporting an explosion, according to the Sri Lankan Ministry of Foreign Affairs. The ship sank rapidly before Sri Lankan Navy vessels could reach the scene.
Sri Lankan authorities reported that 32 survivors were rescued, many in critical condition, while 87 bodies were recovered by Wednesday afternoon. An estimated 61 individuals remain missing, with the frigate believed to have carried a crew of approximately 180 sailors. Sri Lankan Foreign Minister Vijitha Herath briefed parliament on the incident, confirming the identification of the vessel as IRIS Dena and noting that search and rescue operations continued in coordination with regional partners.
At a Pentagon press briefing, Secretary Hegseth described the engagement: “Yesterday, in the Indian Ocean, an American submarine sunk an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo. Quiet death.” He characterized the IRIS Dena as Iran’s “prize ship,” highlighting its advanced capabilities, including surface-to-air and anti-ship missiles, torpedoes, and helicopter operations. Chairman of the Joint Chiefs of Staff Gen. Dan Caine confirmed the strike was executed by an unspecified U.S. fast-attack submarine using a single Mk 48 heavyweight torpedo, which achieved “immediate effect” by detonating under the frigate’s stern and tearing the hull apart.
The Pentagon released declassified video footage showing the torpedo impact, with a large plume of water erupting as the warship split along its port quarter before sinking. The footage, shared publicly on March 4, depicts the dramatic “quiet death” described by Hegseth.
The sinking represents a significant escalation in the ongoing U.S.-Israeli military campaign against Iran, now in its sixth day following initial strikes on February 28, 2026, that killed Supreme Leader Ayatollah Ali Khamenei and numerous senior IRGC commanders. While previous U.S. and Israeli operations focused on airstrikes against Iranian territory, missile sites, and leadership targets, the torpedo attack on IRIS Dena marks the first direct naval engagement involving a U.S. submarine in the current conflict.
Iran has condemned the incident as an “act of state terrorism” and vowed retaliation. Tehran has already launched multiple waves of ballistic missiles and drones targeting Israeli military sites and U.S. assets in Gulf states, including deadly strikes on facilities in Kuwait, Qatar, Bahrain, and others. The loss of IRIS Dena—one of Iran’s most modern domestically produced frigates—deals a blow to the Islamic Republic of Iran Navy’s surface fleet capabilities in the Indian Ocean and beyond.
The strike occurred amid Iran’s effective closure of the Strait of Hormuz to most commercial traffic through threats and military posture, contributing to sharp rises in global energy prices (Brent crude near $82 per barrel) and widespread shipping disruptions. QatarEnergy’s force majeure on LNG exports following earlier attacks has further strained global supplies.
Sri Lanka, maintaining neutrality in the conflict, has focused on humanitarian response, with its navy and coast guard leading recovery efforts. President Anura Kumara Dissanayake expressed condolences over the loss of life and called for de-escalation to prevent further spillover into South Asian waters.
Analysts note that the use of a submarine-launched torpedo—rather than air or surface strikes—allowed for a stealthy, precise engagement in international waters, minimizing immediate risk to U.S. assets while sending a strong signal of extended reach. The Mk 48 torpedo, a heavyweight weapon capable of targeting both surface ships and submarines, remains a cornerstone of U.S. undersea warfare doctrine.
The incident has drawn international condemnation from Russia, China, and several non-aligned nations, who described it as a dangerous escalation. Gulf states hosting U.S. forces have reiterated calls for restraint, while the United Nations Security Council continues to grapple with deadlock on a ceasefire resolution.
As the broader Iran conflict shows no signs of abating—with ongoing missile exchanges, Hezbollah attacks from Lebanon, and persistent Iranian retaliation—the sinking of IRIS Dena underscores the expanding scope and lethality of operations, now reaching into the Indian Ocean far from the primary theater in the Middle East.
The U.S. maintains that the strike was a targeted response to Iranian naval threats and provocations, while emphasizing continued commitment to protecting allies and freedom of navigation. Iran has promised severe consequences, raising fears of further asymmetric responses targeting shipping lanes, energy infrastructure, or U.S. interests regionally.
