Defeating a trailing submarine is easy.
Spray the wake with a biodegradable oil dyed green.
Submarine pops up attack scope for a quick shufti. Oil coats scope with oil so all the skipper sees is green.
Skipper smacks ship control officer round the back of the head and demands periscope depth
Ship control officer knows better than to argue and brings the boat up a bit more.
Skipper has another peek, still green, smack round head, repeat.
Eventually the submarine gets high enough for the trailed ship to shoot it down with a/a fire or missile.
I leave the details to you, my cut is 50%.