Exodus 15:5

Πόντῳ ἐκάλυψεν αὐτούς· κατέδυσαν εἰς βυθὸν ὡσεὶ λίθος.

With open sea he covered them; they sank into the depth like a stone.

תהמת יכסימו ירדו במצולת כמו־אבן׃

*   open sea OR ocean
*   they sank into the depth OR they went down into the bottom