Funnily enough I was watching an old episode of
Kavanaugh QC the other day and the story was about a trawler lost with her crew. The owner and other locals started a conspiracy theory that there had been a collision with a submarine, but he had sent a non seaworthy boat to sea and sabotaged her for the insurance money.. I was reminded of the
tragic loss of the Fishing Vessel Pescado.
As for submarines in deep water, see -
Why Billion Dollar Nuclear Submarines Still Run Into Things Underwater.