[Aktungbby]

http://americanhistory.si.edu/subs/anglesdangles/taming6.html

The tactical speed of a submarine is that speed at which the submarine is quiet enough to remain undetected while tracking enemy submarines effectively, with sources of self-noise reduced to the point that other submarines and ships can be detected using onboard passive sonar sensors. The the maximum burst speed of a submarine is the highest speed that can be achieved by the submarine's propulsion system, regardless of the self-noise created in the process. In the past, the tactical speed of a submarine was typically significantly less than its burst speed, though in the case of the SSN-21 Seawolf it is said that the tactical speed of 25 knots is a significant fraction of the burst speed of the boat.

https://fas.org/man/dod-101/sys/ship/deep.htm Shrouded propulsors are good; Depth is better! The Best Depth for a submarine to avoid detection by a hull-mounted sonar is conventionally regarded as the Sonic Layer Depth plus 100 meters