What Happened
- On March 4, 2026, a US Navy submarine torpedoed and sank the Iranian Navy frigate IRIS Dena in international waters approximately 40 nautical miles (75 km) off Galle in southern Sri Lanka.
- US Defence Secretary Pete Hegseth confirmed the strike, calling it the "first such attack on an enemy since World War II" — the first time a US submarine had sunk an enemy warship since 1945.
- IRIS Dena was a Moudge-class frigate of the Southern Fleet of the Islamic Republic of Iran Navy; it was returning home after participating in India's MILAN 2026 multilateral naval exercise and the International Fleet Review in Visakhapatnam.
- The vessel sent a distress call between 6–7 AM Sri Lanka time; at least 101 sailors were reported missing and 78 wounded, including 32 seriously, according to Sri Lanka's military.
- Sri Lanka's navy and air force launched a search and rescue operation, recovering several bodies; Sri Lankan Foreign Minister Vijitha Herath confirmed no other ship or aircraft was observed near the sinking vessel.
- India's defence and security establishment expressed deep concern over the attack occurring in India's immediate maritime neighbourhood.
Static Topic Bridges
Exercise MILAN — India's Flagship Multilateral Naval Exercise
Exercise MILAN is the Indian Navy's premier multilateral biennial naval exercise, initiated in 1995 with just 4 countries and now one of the world's largest multilateral naval exercises. The 2026 edition at Visakhapatnam hosted 74 participating nations with 85 warships, including 19 foreign warships, alongside the International Fleet Review 2026 and the Indian Ocean Naval Symposium (IONS) Conclave of Chiefs. Iran's participation in MILAN reflects India's longstanding policy of engaging all regional navies as part of its SAGAR (Security and Growth for All in the Region) doctrine.
- MILAN 2026 held in Visakhapatnam in February 2026 — Iran's IRIS Dena was a participating vessel
- IRIS Dena docked at Visakhapatnam on February 20, 2026, following the Fleet Review on February 18
- Exercise includes passage exercises, anti-piracy drills, humanitarian assistance simulations, and port calls
- IONS (Indian Ocean Naval Symposium) meets alongside MILAN and includes 35 Indian Ocean littoral states
Connection to this news: The fact that IRIS Dena had just participated in India-hosted naval exercises and was attacked on its return journey creates a direct link between India's multilateral maritime engagement and the expanding West Asian conflict, raising questions about India's ability to insulate itself from the fallout.
Freedom of Navigation and UNCLOS in the Indian Ocean
The United Nations Convention on the Law of the Sea (UNCLOS), adopted in 1982 and in force since 1994, codifies freedom of navigation as a fundamental right on the high seas (Articles 87, 90) and within Exclusive Economic Zones (EEZ) (Article 58). Warships enjoy complete immunity from the jurisdiction of any state other than their flag state on the high seas under Article 95. The attack on IRIS Dena in international waters — which is within neither US nor Sri Lanka's territorial waters — raises significant questions about the legality of attacking a warship in a third state's proximate waters.
- High seas begin beyond 12 nautical miles from any coastal state's baseline
- UNCLOS Article 95 grants warships immunity from flag state jurisdiction on the high seas
- India ratified UNCLOS in 1995 and has consistently advocated for freedom of navigation
- A submarine attack on a warship in international waters is an act of war under traditional international law
- Sri Lanka's EEZ extends 200 nautical miles; 40 nautical miles off Galle falls within Sri Lankan EEZ
Connection to this news: The strike 40 nautical miles off Sri Lanka — within Sri Lanka's EEZ but on Iranian sovereign property (a warship) — places Sri Lanka in a legally and diplomatically sensitive position and underscores how the US-Iran conflict is expanding beyond the immediate Gulf theatre into the Indian Ocean, directly impinging on India's strategic backyard.
India's Indian Ocean Security Architecture — SAGAR Doctrine
India's SAGAR (Security and Growth for All in the Region) doctrine, articulated by Prime Minister Modi in 2015, positions India as a "net security provider" in the Indian Ocean Region (IOR), committed to freedom of navigation, maritime connectivity, and collective security. India's Maritime Security Strategy (2015) identifies the Indian Ocean as India's primary area of strategic interest. The sinking of a warship 40 nautical miles off Sri Lanka's southern coast directly challenges the stability of India's near-abroad.
- India maintains a naval presence across the Indian Ocean through island territories (Andaman & Nicobar, Lakshadweep) and bilateral arrangements
- India's Maritime Domain Awareness (MDA) network — including the Information Management and Analysis Centre (IMAC) — covers the IOR
- India has defence cooperation agreements with Sri Lanka, Maldives, and Mauritius for maritime surveillance
- The Indian Ocean accounts for ~90% of India's seaborne trade
Connection to this news: A US submarine operating within Sri Lanka's EEZ to sink an Iranian warship — without Sri Lanka's knowledge or consent — signals a dramatic erosion of the rules-based maritime order in India's primary strategic theatre.
Key Facts & Data
- IRIS Dena: Moudge-class frigate, Southern Fleet of the Islamic Republic of Iran Navy
- Attack location: ~40 nautical miles (75 km) off Galle, southern Sri Lanka
- Casualties: 101 sailors missing, 78 wounded (32 seriously) per Sri Lanka's military
- This is the first US submarine attack on an enemy vessel since World War II (confirmed by Pentagon)
- MILAN 2026: 74 participating nations, 85 warships, hosted in Visakhapatnam, February 2026
- IRIS Dena had docked at Visakhapatnam on February 20, 2026
- Sri Lanka launched naval and air force search-and-rescue operations; several bodies recovered
- India's defence establishment has expressed serious concern over the proximity of the conflict