Defence Secretary Pete Hegseth confirmed at a Pentagon midday briefing that a US submarine sank the IRIS Dena with a torpedo 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." Sri Lankan defence officials had assessed the attack profile as consistent with a submarine strike when the sinking was first reported; the Pentagon has now confirmed the method and the weapon.
The last time the US Navy torpedoed and sank an enemy warship was in the Pacific in 1945. Operation Praying Mantis in April 1988 — the most recent US-Iran naval engagement — destroyed Iranian vessels with Harpoon anti-ship missiles and five-inch naval gunfire in the confined waters of The Persian Gulf. The distinction matters. Missiles and gunfire are surface engagements: the attacker is visible, the defender has warning, and the engagement occurs in a defined operational zone. A torpedo fired from a submarine the target cannot detect, in open ocean, against a vessel thousands of kilometres from any front line, communicates something different — that Iran's remaining naval assets are vulnerable everywhere, at any time, with no prospect of evasion or advance warning.
Hegseth's phrasing — "thought it was safe" — was pointed. The Dena was not on a combat patrol. It had participated in India's International Fleet Review 2026 and Exercise MILAN at Visakhapatnam, a biennial multilateral naval exercise with diplomatic functions running since 1995. The frigate was transiting home when the war began, at its maximum possible distance from Iranian waters, after a goodwill port call with a non-belligerent. It was sunk 40 nautical miles from Sri Lanka — a country with no part in this conflict.
International humanitarian law permits the targeting of enemy warships in international waters during armed conflict. That legal question is settled. The political question is separate and will persist longer. India hosted the Dena at Visakhapatnam; Indian warships exercised alongside it days before a US submarine destroyed it. Sri Lanka is recovering its dead. Both nations' navies operate in waters where the United States has now demonstrated it can sink vessels at will. For New Delhi in particular — which has spent decades building its own Indian Ocean naval authority — the kill establishes a fact that extends well beyond this war: American submarine power in the Indian Ocean is unchallenged and, for any surface vessel, undetectable.
