Iran conflict 2026: US announces submarine torpedo strike on Iranian warship

Iranian Navy frigate IRIS Dena is shown during the Indian Navy International Fleet Review on 18 February 2026 near Visakhapatnam, India. (Michael Nitz, Naval Press Service)

A US fast attack submarine (SSN) struck an Iranian surface warship with a Mk 48 heavyweight torpedo during the first 100 hours of the combined US and Israeli forces attack on Iran, US military officials confirmed on 4 March.

The attack would mark the first time since 1945 that an SSN has sunk an enemy combatant ship with a torpedo, Pentagon officials said.

The surface ship, shown in the Pentagon's released video of the submarine's torpedo strike in the Indian Ocean, is highly likely to be Iranian Navy frigate IRIS Dena (75).

Dena participated in the Indian Navy's International Fleet Review 2026, and was photographed on 18 February 2026 during the event near Visakhapatnam, India.

“In the Indian Ocean … an American submarine sunk an Iranian warship that thought it was safe in international waters,” US Secretary of Defense Pete Hegseth said on 4 March during a press conference at the Pentagon.

“We've destroyed more than 20 Iranian naval vessels and effectively neutralised at this point in time Iran's major naval presence in theatre,” General Dan Caine, Chairman of the Joint Chiefs of Staff, said during the press conference. The Iranian ship (identified by Janes as highly likely to be Dena ) was sunk with a single Mk 48 torpedo, Gen Caine said.