Good stuff Caz
I am not sure about the ASW frequency capabilities, and the various naval assets around the world may not wish to "advertise" all their capabilities.
At least we know the passive sonar can easily detect very low freq sounds like propellors that are turning. Apparently, they can detect higher freq sounds like whale calls, which seem to be at upper range of human hearing.
Listening for "pings" that are up in the near ultrasonic range sould not be that hard for the ASW sonobouys or maybe subs. You don't need more than one ASW plane like the Orion or the new USN one to drop a dozen sonobouys in a very good pattern. The problem is revealing military capabilities. Up to me I would claim we found the beacon a hundred miles away! OTOH, if you drop a good pattern within a few clicks and don't detect the ping before the French boat does, then.........