After a U.S. submarine sank Iran’s IRIS Dena with a Mk 48 torpedo, attention turned to the Navy’s primary undersea weapon that first entered operational service in 1972.

A single Mk-48 torpedo achieved "immediate effect" on an Iranian frigate, which was operating in the Indian Ocean, the Pentagon confirmed.

The U.S. Navy will occasionally sink its own old, unwanted ships, but it's an expensive business, so why would it want to do a thing like that?

Since 1991, Navy subs have launched scores of cruise missiles in combat, but the torpedo attack off Sri Lanka is a return to form after 80 years.