I've been wondering myself why they were not using active sonar.
Is that common practice during peacetime? If so, why? Who are we hiding from?
/stupid questions
"Who are we hiding from?"
You can't hide a nuke sub that is doing 30 kts. Subs do not run silent at that speed. So why no active sonar? A very good question. Next question: At 30 kts, would active sonar have given them warning soon enough to avoid the "mountain"?
Active sonar frequency range is designed to localize discrete metal objects --AKA "targets".
Regardless of what you see on "Voyage to the bottom of the Sea" and Hollywood movies, it is very poor for general navigation.
Everybody.
Finally, a question I can answer!