[John Pancoast]

Also the game's escorts, etc. have two states; non-alert and alert. The alert status gets brought on by various things. I.e., torpedo a ship, get seen visually, heard/found submerged, etc.
Once in alert status they are more likely though not guaranteed to find you again, even if they briefly lose you. It can also and usually does cause other escorts to come join in the hunt many times without you even knowing they're there.