Noise in a hull generated by flowing water depends on the bow shape and from apertures in the flooded parts of the hull, both of which contributes to create vortexes. Classic WW2 submarines like the type VII or IX had myriads of slots in the outer skin to allow water passage and reduce diving time by quickly flooding the space below the deck and avoid bubbles of gas to be trapped between the skin and the hull. In a later type XXI (or in a similar post war submarine) the number of slots was reduced and their placement and shape became extremely important.
Another critical area is the sail and, of course, anything sticking out of the hull itself, ie a rudder, a plane or -in past times- a deck cannon. Everything that can create local vortexes is a potential source of unwanted sounds and drag.
Back on shape and hydrodynamic efficiency...
If we have to observe fishes and marine animals, Mother Nature solution for a perfect underwater craft, there are several different shapes that appear to be optimized for speed and fuel (err... food) economy.
Sperm whales, for example, don't adopt a teardrop shape, yet they are among the biggest marine animals that ever traveled oceans and they are capable and fast swimmers (up to about 40km/h - 22 kts). Interestingly, the hull shape and the bow of several post war German submarines resembles more the shape of a sperm whale than that of a blimp. (Type 206-209, TR1700)
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