Why was the submarine created?

The submarine was envisioned by ancients who would sail the seas in ships of their time and dream of a weapon that could ply the deep. This undersea vessel could attack and sink opposing ships from below, taking them completely by surprise and remaining largely impervious to their attacks. But technology had a long way to go to make anything like a practical submarine possible. It was not until the 17th century that anything could be constructed, and the technology still struggled to solve the issues with sealing a hull against pressure, propulsion, weapons, buoyancy, and crew survival.

So that we can explore the beauty of the sea and we could see al the living things in the sea.