Stealth factor of your U-boat.

It depends on the following factors:

Speed – The faster you run, the more noise you make, so the player will be detected easier with the hydrophone.

Distance – The closer you are to an escort, the more efficient their sensors are - hydrophone, sonar and look out (visual).

Aspect – Your profile exposed to an escort will make harder (front or back) or easier (side) to be detected.

Height – The higher the U-boat silhouette above water (including raised periscope), the easier will it be spotted (or detected with radar).