What Happened
- The Iranian Navy frigate IRIS Dena was torpedoed and sunk by a United States Navy submarine on March 4, 2026, in international waters approximately 40 nautical miles off the coast of Galle, Sri Lanka, killing at least 87 crew members with over 30 rescued.
- The warship had participated in India's flagship multilateral naval exercise MILAN 2026 and the International Fleet Review (IFR) 2026, held in Visakhapatnam from February 15 to 25, 2026, and was returning home when it was struck.
- The US Department of Defense confirmed the attack was carried out using a Mark 48 torpedo, making it a direct military engagement in the Indian Ocean region and raising acute concerns about maritime security near India's strategic waters.
- Sri Lanka launched rescue operations, and a second Iranian ship was reported to be heading toward the area after the submarine attack.
- India's Navy and Defence Ministry confirmed the IRIS Dena's participation in IFR-MILAN 2026, placing India in a diplomatically sensitive position as its invited naval guest was destroyed by a US strike in waters near the subcontinent.
Static Topic Bridges
Exercise MILAN: India's Flagship Multilateral Naval Exercise
MILAN (Meeting of International Navies) is a biennial multilateral naval exercise hosted by the Indian Navy, conceived to foster interoperability, maritime cooperation, and goodwill among friendly foreign navies. First held in 1995 with just four countries, it has grown into one of the largest multilateral naval events in the Indo-Pacific.
- MILAN 2026 (13th edition) was held at Visakhapatnam from February 18-25, 2026, under the Eastern Naval Command.
- A record 74 countries participated, deploying 42 warships, submarines, and 29 aircraft, including 18 ships from partner navies — the largest iteration in the exercise's history.
- The 2026 edition was part of a naval trifecta: IFR 2026 + MILAN 2026 + 9th IONS Conclave (Indian Ocean Naval Symposium), all held simultaneously in Visakhapatnam.
- New entrants in 2026 included Germany, the Philippines, and the UAE.
Connection to this news: The IRIS Dena was one of the participating vessels at MILAN 2026 and the IFR, representing Iran. Its destruction by the US Navy just days after departing Indian waters has placed India's maritime diplomacy at the centre of a geopolitical controversy.
India-Iran Bilateral Relations and Chabahar Port
India and Iran have historically maintained strategic and economic ties centred on energy imports, the Chabahar port project, and the International North-South Transport Corridor (INSTC). Iran was India's third-largest oil supplier before US sanctions progressively curtailed imports.
- In May 2024, India and Iran signed a 10-year long-term agreement for India Ports Global Limited (IPGL) to operate the Shahid-Beheshti terminal at Chabahar port, with India committing $250 million in loans and $370 million in infrastructure investment.
- Chabahar provides India a direct maritime route to Afghanistan and Central Asia, bypassing Pakistan — a strategic counter to China's Gwadar port in Pakistan.
- In February 2025, the Trump administration revoked all sanctions waivers allowing Indian work at Chabahar, adding pressure to the bilateral relationship.
- Foreign Secretary Vikram Misri visited the Iranian Embassy in New Delhi on March 5, 2026, to condole the death of Supreme Leader Khamenei.
Connection to this news: India's invitation to an Iranian warship to participate in MILAN 2026 reflected the continuing strategic relationship; the ship's sinking by the US creates a diplomatic dilemma for India, which maintains partnerships with both Washington and Tehran.
Maritime Security in the Indian Ocean Region (IOR)
The Indian Ocean Region (IOR) is of paramount strategic importance to India given its peninsular geography, dependence on sea lanes for trade and energy, and status as a net security provider in the region. India's maritime doctrine emphasises SAGAR (Security and Growth for All in the Region).
- Over 90% of India's trade by volume and nearly 80% by value moves through sea lanes, making freedom of navigation a core national interest.
- India's Exclusive Economic Zone (EEZ) spans 2.37 million sq km; the Indian Ocean carries roughly 50% of global container traffic.
- The sinking of a naval vessel in international waters near Sri Lanka — within India's traditional sphere of maritime influence — marks a significant escalation of conflict into the IOR.
- India pursues a "net security provider" role in the IOR through bilateral exercises, hydrographic cooperation, and patrol coordination with littoral states.
Connection to this news: The IRIS Dena's destruction just off Sri Lanka's coast brings active military hostilities within India's near-abroad, testing India's SAGAR doctrine and its ability to maintain the Indian Ocean as a zone of stability.
Key Facts & Data
- IRIS Dena: Iranian Navy frigate; participated in MILAN 2026 and IFR 2026 at Visakhapatnam (Feb 15-25, 2026).
- Location of sinking: ~40 nautical miles off Galle, Sri Lanka (Indian Ocean).
- Casualties: At least 87 killed; 30+ rescued; second Iranian vessel dispatched to the area.
- Weapon used: Mark 48 torpedo, fired by a US Navy submarine (confirmed by US DoD).
- MILAN 2026 scale: 74 nations, 42 warships, 29 aircraft — largest edition in exercise history.
- Chabahar port: India signed a 10-year operational agreement with Iran in May 2024.
- India's IOR EEZ: 2.37 million sq km; over 90% of Indian trade is seaborne.