A North Korean submarine is missing and presumed sunk, according to various reports.
The vessel was operating off the North Korean coast for several days when it disappeared, reports say that American satellites, aircraft and ships have been watching as the North Korean navy searched for the missing submarine.
North Korea reportedly operates a fleet of 70 submarines, mostly are old diesel models capable of little more than coastal defence.
This latest incident comes at a time of heightened tension in the region as South Korea and the US continue their largest-ever military exercise. North Korea has of course issued another threat of war over the drill.
According to the US Naval Institute journal, the US Navy was tracking the submarine when it suddenly disappeared.