You do know we can detect those right? Almost everytime Subs were never in play. Because Sonar exists for a reason.
Active can give a ship away just as well as a visual look. So passive is used when no need.
We are also limited in our capabilities during training.
I can assure you, in actual war we won't be so nice in what we use, and the enemy can not hide.
People always go "You see, a diesel sub can sneak up on a carrier fleet!" And they fire a torpedo that doesn't kill the ship, give them selves away and die a horrible death.
In a real combat situation, of a sub gets close enough to launcha torpedo, it will be the last thing it ever does, as well as what ever the country did to do that.
@Sailor.X you were in the Navy. How true are these claims?