> The ocean is very, very deep. The Titanic is "relatively" shallow, only 3800 feet below sea level

It's 3800 meters, 13000 feet as you wrote in the first paragraph.

Nothing shallow about 3800m deep, that's abyssal plains level, it's basically the bottom of the "normal" ocean (the abnormal ocean being the hadal zone of the trenches). It's a land of no light, little to no oxygen, and literally freezing cold.