The underwater mountain was actually a dastardly CCP plot. You see in the DPRK they have Juche necromancy, much less well known is China's Marxist superpower of quickly constructing anything they want, including a whole mountain under the ocean that didn't exist on the US navy's charts.

One day they're cruising happily around underwater, the next that mountain that wasn't there 48 hours ago is in their patrol path and bam, coyote on painted tunnel type damage. Meanwhile Xi Jinping is snickering in the background.