[LukeFF]

Originally Posted by WernerSobe

I disagree. If you read the manual carefully you will see that in case of the fleet boat only ultrasonic sonar was working on surface. The game doesnt differ you only have passive sonar but in reality there were two different passive sonars. The normal hydrophone and the ultrasonic high frequency sonar.

The hydrophone head is mounted on deck (above the water) and is for listening for ships.

The ultrasonic dome is mounted underneath the hull. The heads look like two bubbles. This device is however not capable to catch ship sounds at far distances. Its primary role was to catch enemy high frequency pinging and minefield navigation. Theoreticaly you can catch ship sounds or actualy only their very high frequencies, but since the ultrasonic sound is not traveling far by nature - you may catch a sound of a ship that is 500 yards away but not much further.

So it is not realistic, you cannot catch sound contacts that are 20 km away when surfaced.

What he said. Otherwise, the only correction that needs to be made is that American ultrasonic sonar could pick up ship sounds up to 7,000 yards away, for a single ship contact - not much when you consider sonic sonar could pick up single contacts 10,000 yards away.

Here's a nice chart that gives a good idea of American sensor capabilites at the peak of their development, as published in Submarine Warfare Instructions:

Average Detection Ranges for Submarine Sensors, 1945 (x1000 yards, 50 percent detections)

Independent merchant ship: QB/JK: 7..JP: 10..Enemy Sonar: 17..Periscope: 12.5..SJ-1: 17
Convoy: QB/JK: 10..JP: 15..Enemy Sonar: 17..Periscope: 17..SJ-1: 19
Independent Combatant: QB/JK: 7..JP: 10..Enemy Sonar: 17..Periscope: 10..SJ-1: 10.5
Escorted Combatant: QB/JK: 15..JP: 20..Enemy Sonar: 17..Periscope: 17..SJ-1: 25

QB/JK is ultrasonic sonar. JP is sonic sonar. RFB uses an average of the 4 values for JP sonar (13,750 yards)