In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Submarine
If you are travelling inside a submarine then you will have much distress, while if you see a submarine from afar then someone close to you will act in an underhand manner in order to harm you.