Dunno about the actual range of WWII sonar, my only real world experience was with the AN/AQS-13A dip sonar in SH-3 Sea King helicopters. Max range setting on that was 20,000 yards, but depending on how loud the sound was and how much ambient noise interference there was (the real ocean is noisy as hell with "biologicals" and other stuff) and the thermal layers you could pick up sounds twice that far, or be unable to hear cavitating screws 2000 yards away. SOP if you thought you heard something (and there were two of us plugged into the sonar set) was to tell the pilot, who would order the hydrophone retracted, fly a couple miles in the direction of the suspected contact, go into a hover and order the sonar lowered again. Got a more firm contact in that location we'd raise the sonar and break hover again to move in the new direction and try again, repeat until we found it was merely a wreck on the bottom with the current banging something against something else.
Hunting surface ships is a lot easier, I never did find Red Oktober.
