Per M. Stradbury:
Is it true (or an urban myth) that a swimmer would be sucked
under (presumably to drown) when a capital ship sinks?

Dunno what a capital ship is but am guessing it's big.

I saw an interview clip in which Lord Louis Mountbatten told of
surviving his destroyer's sinking - along with a senior NCO who said at
the time something like "Well sir, the scum always rises to the surface"
so I am guessing that both were in the water when the ship went down
under them.

--
Pete Cresswell