hydrophone.
 

has anybody been able to identify the different warships (aircraft carriers,battleships,cruisers,light cruisers) by listening to the hydrophone? Is their a identification log floating around out there?Is their a way to plot distance with the hydrophone?(to keep from pinging).Would their be a good convoy attack guide out there too?...thank you

Lots of that stuff in the "Sub Skipper's Bag of Tricks" thread that is stickied above :up:

http://www.subsim.com/radioroom/showthread.php?t=146795