Military sonar on submarines has killed a lot of blue whales.
Do you have any idea how terrible an idea using active sonar on a submarine is?
Anything out there will detect you at twice the range you can detect them. It totally blows any stealth ability you have and stealth, of course, is the only thing that makes submarines a useful weapons system.
Yes, the military tests active sonar, and submarines are equipped with it. However, the idea that the tree huggers have that all submarines go tearing around the oceans at high speed blasting their active sonar all the time...good grief. No.