We are currently on station in our assigned exercise area. An old and obsolete submarine has had its weapons and sensors removed and is approximately 10 nautical miles to your north.

Your frigate is equipped with a AN/SQS-26CX Hull Sonar; the bleeding edge of sonar technology when it was first introduced in the 1960's. The SQS-26CX is capable of operating in passive mode and active mode. Passive mode is always operating, there is no action required from the player. Active mode needs to be turned on in the sensors dialog (F9) or in the EMCON section of the right hand status bar.

Active sonar is very much like radar in that it sends out energy--in this case sound energy--and analyses the returned energy that is reflected off objects in order to make detections. Like radar, active sonar is also not generally able to determine the identity of an object--merely its presence and location. A corollary of this is that using active sonar also gives away your presence, as well as possibly your location and identity in much the same way that using radar does.

Passive sonar simply listens to sounds in the water and analyses their characteristics to detect and identify contacts. With enough sound data contacts can be identified right down to individual vessels within a class, and if the contact is held for long enough a good estimation of position can be made. Unlike active sonar, the use of passive sonar gives no outward indication that can be detected by other platforms.

Sonar in both its active and passive forms is affected by external noise, the most important factor contributing to external noise is the speed of the platform the sonar sensor is attached to. For surface ships, passive sonar is of minimal use above about 5 knots. Active sonar can still make detections at speeds up to around 20 knots but the range at which objects are detected is reduced markedly as speed increases.

Leave the sensor settings at their pre-set state for now and move north at 5kts until you make passive sonar contact.