The depths have covered them: they sank to the bottom as a stone.
All Commentaries on Exodus 15:5 Go To Exodus 15
Augustine of Hippo
AD 430
But if our enemies “went down into the depths like a stone,” the only ones the devil remains in possession of and the only ones who have the hardness of the devil are those about whom it is written, “When the sinner has come into the depths of evil, he behaves disdainfully.” They don’t believe, you see, that they can be forgiven for what they have done; and in that mood of despair they plummet to greater depths than ever.
