There are much, much better ways of doing that than a surface ship that makes creaks, engine noises, crew sounds, waves hitting the hull, etc.

"FLIP has no engines or other means of propulsion. It must be towed to open water, where it drifts freely or is anchored. http://en.wikipedia.org/wiki/RP_FLIP

It likely has a diesel generator for electrical power, though. Either way, it has nothing on the alternatives for detecting subs.

Marine Physics Lab was part of Scripts Institute of Oceanography - scientists there from around the world - doesn't seem like the kind of place where classified work would be done.

> doesn't seem like the kind of place where classified work would be done.

They get a lot of money from the Office of Naval Research, and some of the projects are certainly classified. I dont know for sure, but it's quite possible that FLIP was used at some point for studies of acoustics, which were paid for by people fundamentally interested in finding submarines.

We already have a way to do this with hydrophones. http://en.wikipedia.org/wiki/SOSUS