Pete Hegseth called it ‘quiet death’—the first time a U.S. sub fired a torpedo and hit an enemy ship since the 1940s

A U.S. submarine sank the Iranian frigate IRIS Dena off the southern coast of Sri Lanka on Wednesday, killing 87 people.

The submarine struck the ship with a torpedo, U.S. Defense Secretary Pete Hegseth said, resulting in “quiet death”.

The event marks the first time a U.S. submarine has launched a torpedo in combat or engaged and destroyed a ship since the second world war.

Why is this old weapon reappearing now? And for that matter, what are torpedoes? Can ships defend against them, or even see them coming?