Can a high-speed submarine simply run as fast as its engines can propel it underwater?
Short answerNo. Safe speed is limited by underwater navigation and topography, while high speed also increases noise and reduces the time available to avoid hazards.
NotesA nuclear boat's low-speed quiet setting differs sharply from its much noisier high-speed case. The faster the submarine moves, the less time it has to recognize and avoid seabed features or other hazards, so underwater topography becomes the practical limit. Historical collisions with the seabed reinforce that the danger is operational rather than theoretical. Even in deep water, a submarine running at 40 knots only about 100 meters down may disturb the surface enough to leave a detectable wake.