[LukeFF]

Originally Posted by Frederf

Correct me if I'm wrong but the normal sound frequency stuff is the two "balls" below the hull and is responsible for passive listening. The complete sonar/hydrophone set includes the "T-bar" fore deck device which allows ultra-sonic (higher than human hearing frequency range) operations such as pinging.

You got it in reverse:

http://www.hnsa.org/doc/fleetsub/sonar/chap1.htm#1A