“For a submarine’s crew to be provided with collision-warning, its active sonar has to be operating. While this can be activated to see if there any obstacles in the submarine’s path, in many operational scenarios the active sonar is not an option since it emits signals that other submarines and ships can detect.”
Utter BS.
Why?
I would imaging that passive sonar would have noticed the not-particularly-stealthy cargo ship if anybody had really been listening.