In order to better understand the sentence, let’s dissect it.
“Carcasses of many a tall ship.”
What are many a tall ship? Many tall ships.
What are carcasses? Skeletons.
What do you think of when you hear “skeletons of many ships”? A dark or bright place?
Where are skeletons of HUMANS kept?
Carcasses of many tall ships lie in an underwater ________.
Carcasses of many humans lie in a ________.
(HINT: starts with the letter G).
Both of these answers are the same, and should explain what the sentence means.