Watch: Iranian warship strike near Sri Lanka raises questions for India

What Happened

On March 4, 2026, a US Navy fast-attack submarine torpedoed and sank the Iranian Navy frigate IRIS Dena in international waters approximately 25 miles south of Sri Lanka.
The IRIS Dena had participated in India's MILAN 2026 multilateral naval exercise at Visakhapatnam (February 18-25, 2026) and was sailing home to Iran when it was struck.
The attack killed at least 87 crew members; at least 61 others remained missing. Thirty-two survivors were rescued by the Sri Lankan Navy and taken to Galle National Hospital.
The US Secretary of Defense Pete Hegseth confirmed the US submarine had fired the torpedo.
The event is historically significant: it is the first time a nuclear-powered submarine has sunk an enemy surface vessel since the Royal Navy's HMS Conqueror sank ARA General Belgrano during the Falklands War (1982), and the first such action by a US submarine since World War II.
For India, the sinking raises acute strategic questions: an Iranian warship that had just participated in a friendly Indian naval exercise was attacked by India's strategic partner (the US) in waters close to Indian shores — creating a difficult diplomatic and strategic position.
The incident occurred in the context of the broader Iran-US-Israel conflict that had erupted in late February 2026 and which prompted the closure of the Strait of Hormuz.

Static Topic Bridges

MILAN Naval Exercise: India as an Indo-Pacific Maritime Hub

MILAN is India's flagship biennial multilateral naval exercise, first launched in 1995 from the Andaman and Nicobar Command. It has grown from a four-nation exercise to one of the world's largest multilateral naval events.

MILAN 2026 (13th edition): Held at Visakhapatnam, February 18-25, under the theme "Camaraderie, Cooperation, Collaboration."
Participation: 74 nations, 85 warships (including 19 from foreign navies), 29 aircraft — the largest edition in MILAN's history.
New participants in 2026: Germany, Philippines, UAE (with military assets for the first time).
The exercise included the International Fleet Review (IFR) aboard INS Vikrant, India's domestically built aircraft carrier.
Iran's IRIS Dena was among the participating warships — reflecting India's policy of maintaining defence engagement with all major regional powers.

Connection to this news: Iran's participation in MILAN was an expression of India-Iran defence ties. The sinking of IRIS Dena just days after it left India's naval exercise put India in the position of having extended hospitality to a vessel that the US then destroyed — a profound diplomatic complication.

India's Strategic Autonomy in the Indian Ocean Region

India's foreign policy doctrine in the maritime domain is captured in the concept of SAGAR (Security and Growth for All in the Region), articulated by Prime Minister Modi in 2015. It envisions India as the preferred security partner for Indian Ocean littoral states — a net security provider.

The Indian Ocean Region (IOR) is central to India's strategic calculus: 90% of India's trade and over 80% of its energy imports transit through IOR sea lanes.
India has signed Logistics Exchange Memoranda of Agreement (LEMOAs) and related agreements with the US, France, Australia, Japan, and other partners for access to military facilities, reflecting defence alignment without formal alliance.
India maintains simultaneous defence ties with the US (via Quad, bilateral defence agreements), Russia (historical partner, supplier of defence platforms), and Iran (through the Chabahar port agreement and historical ties).
The principle of "strategic autonomy" — non-alignment with any single power bloc — underpins India's resistance to choosing sides in great power conflicts.

Connection to this news: The IRIS Dena sinking directly tests India's strategic autonomy framework: India must respond diplomatically to a US military action in its near neighbourhood that killed guests of an Indian naval exercise, without alienating either Washington or Tehran.

India-Iran Relations: Chabahar and Regional Connectivity

India and Iran share a multi-dimensional relationship rooted in civilisational ties, energy trade, and strategic geography. The relationship gained renewed economic significance through the Chabahar Port project.

Chabahar Port (Shahid Beheshti terminal) in Iran's Sistan-Baluchestan province: India has invested in developing and operating this port, which provides an alternative route to Afghanistan and Central Asia bypassing Pakistan.
In May 2024, India signed a 10-year contract with Iran for operating the Shahid Beheshti terminal at Chabahar — its first overseas port operation contract.
Chabahar is part of the International North-South Transport Corridor (INSTC), connecting India to Russia and Central Asia through Iran.
Iran was a major crude oil supplier to India before US sanctions under the Trump administration (2018) forced Indian refiners to halt purchases.
India's relations with Iran are consistently balanced against US pressure — making the IRIS Dena episode another chapter in this complex triangular equation.

Connection to this news: The sinking of an Iranian naval vessel in India's maritime neighbourhood, after participation in an Indian exercise, will inevitably strain India-Iran relations if India is perceived as having facilitated — through intelligence or indifference — an attack on a guest nation's warship.

The attack on IRIS Dena in international waters raises questions under international law, particularly the United Nations Convention on the Law of the Sea (UNCLOS) and the rules governing use of force at sea.

UNCLOS (1982), to which India is a signatory, defines international waters (high seas) as beyond Exclusive Economic Zones (200 nautical miles from baseline); warships of all states enjoy freedom of navigation on the high seas.
Under international law, attacking a warship on the high seas constitutes an act of war unless it is in self-defence or authorised by a UN Security Council resolution.
The US justified the attack within the context of the ongoing Iran conflict; the legality has been contested internationally.
The incident has been compared to the Falklands War sinking of ARA General Belgrano (May 2, 1982) — also a vessel on the high seas — which remains controversial in international law scholarship.
Sri Lanka, whose Navy rescued survivors, took custody of at least one Iranian vessel in the aftermath, placing a non-aligned country at the centre of a major-power confrontation.

Connection to this news: India, as an Indian Ocean power and a coastal state in whose near waters the attack occurred, has a stake in how these international law questions are resolved — particularly since India's own maritime interests depend on established norms of freedom of navigation.

Key Facts & Data

Vessel attacked: IRIS Dena (Iranian Navy frigate)
Date of attack: March 4, 2026
Location: International waters, approximately 25 miles south of Sri Lanka
Method: US Navy fast-attack submarine, single Mark 48 torpedo
Casualties: at least 87 killed; at least 61 missing; 32 survivors (rescued by Sri Lankan Navy)
Historical significance: first nuclear submarine sinking of a surface vessel since Falklands War (1982)
MILAN 2026: February 18-25, Visakhapatnam; 74 nations, 85 warships, 29 aircraft
IRIS Dena had attended MILAN 2026 and was en route home to Iran when struck
India's Chabahar contract: 10-year operational contract signed May 2024
SAGAR doctrine: articulated 2015, frames India as net security provider in IOR
India's IOR stakes: 90% of trade, 80%+ energy imports transit Indian Ocean sea lanes