Coagie has pointed out that most of the naval ASW gear is not optimized for the high freq beacon we are looking for.
One current sonobouy system only goes up to 2400 Hz or so with any good sensitivity. I would imagine the subs to have much larger bandwidth, but just try to get the specs for those!!!!
As Lonewolf said, "dipping" by ASW choppers ain't gonna work. The gear is not real good when passive and needs to "ping". It is not designed for deep work, as most operational subs won't be down there at a thousand meters or more, ya think?
I would place my bets on a sub, but they can't down to the depths we are looking at, but might get a "ping" if the acoustics are right.