Here's a project that used a passive listening device on a wave glider: http://www.fondriest.com/news/wave-glider-robots-listening-tagged-marine-animals-part-w

Here's a project that used a passive listening device on a wave glider: http://www.fondriest.com/news/wave-glider-robots-listening-tagged-marine-animals-part-wired-ocean.htm http://www.fondriest.com/news/wave-glider-robots-listening-t... The whale monitoring I'm familiar with is all passive listening as well. The navy has a long history of pissing off marine mammal experts by blowing things up underwater, so it makes sense that the Office of Naval Research wouldn't fund active sonar. So your recollection has elements of truth.