The Federation Naval Patrol is basically Starfleet for oceans so as a (sub)surface force what kind of equipment does it need? At first I thought it could get away with sensors and transporters only, but if it's doing serious oceanographic research it probably needs vessels. Also transporters are never used all that much in a surface to surface role given flying cars and trains still exist, which is another point toward have vessels of some sort. If they have ships would they just be buoyant hulls with a small power source running a prop for maximum efficiency, or would they make purpose designed submersible shuttles and large ships with full flight capability? Would they fully optimize it for sea movement, or is Trek tech so easy to make and versatile would they just use normal systems like impulse engines and warp cores? Would they go so far as to make a warp capable sea vessel given they are a Federation wide organization, or is that excessive?