U.S. Submarine Sinks Iranian IRIS Dena in International Waters

A submarine of the United States attacked the Iranian warship IRIS Dena, which subsequently sank in the Indian Ocean, around 40 nautical miles off the southern coast of Sri Lanka near Galle.

• The attack took place on March 4, 2026, when a Virginia-class submarine of the United States Navy reportedly fired a torpedo at the vessel. At least 83 personnel were killed, while the Sri Lanka Navy rescued 32 injured sailors, who are currently receiving treatment at a public hospital in the Galle district.

Warship Returning from International Fleet Review

• The Iranian frigate IRIS Dena was returning to Iran after participating in the International Fleet Review 2026, a global maritime exercise held in Visakhapatnam in India.

• After departing the exercise on February 25, the vessel had moved into international waters, meaning it was outside the territorial jurisdiction of any country at the time of the attack.

Rare Use of Submarine-Launched Torpedoes

• The sinking of IRIS Dena represents the fourth instance since the end of World War II in which a ship has been sunk by a submarine-launched torpedo. It is also reported to be the first time the United States has torpedoed an enemy vessel since World War II, marking a significant development in modern naval warfare.

Understanding International Waters

• International waters, commonly referred to as the “high seas,” are parts of the ocean that do not fall under the jurisdiction of any single country. Their legal framework is governed by the United Nations Convention on the Law of the Sea (UNCLOS).

Under UNCLOS:

• A country’s Exclusive Economic Zone (EEZ) extends up to 200 nautical miles from its coastline.
• Within this zone, a coastal state has special rights over exploration and use of marine resources, including fishing and energy extraction.
• Beyond the EEZ lie international waters, where no country exercises sovereignty.

Territorial Waters vs EEZ
International maritime law distinguishes between territorial waters and the EEZ:

• Territorial waters extend up to 12 nautical miles from a nation’s coastline and are treated as an extension of the country’s land territory.
• The Exclusive Economic Zone grants economic and environmental rights, but not full sovereignty.