A modern submarine, designed to spend most of its time submerged, is shaped like a teardrop, the most aerodynamically "slippery" shape, designed to go as fast as possible in a fluid by minimizing friction. It will be round, blunt and wide up forward, tapering to a point aft.

A vessel designed to operate on the surface has sharp bows to cut through the air/water interface, but rounder below the waterline. Narrow bows mean loss of buoyancy, so bows are long and thin to give them enough buoyancy to stay afloat. The stern is usually rounded and short aft, to keep the ship from being "pooped" by a wave coming from behind and to provide buoyancy without having to be long. Of course, the ship's design is greatly dictated by its mission.

Older warships, particularly battleships, usually had their weight concentrated amidships, with armored, heavy gunmounts and barbettes near the superstructure and long thin bows and sterns to provide the needed buoyancy fore and aft. Nowadays, when stealth requirements force ships to have weird shapes to avoid radar detection, and gun platform stability is less important for guided weapons, you are starting to see some more extreme looking surface vessels.

Just for fun, here are three small warships (destroyers) for comparison.
All were named USS Dewey

World War II

Vietnam Era (my old ship)

The latest Dewey, just recently commissioned