In short, if it's heading away, there is not much you can do except report the contact on radio. If it's heading for you, like the battleship TF I encountered awhile back, get their general course run at full speed to intercept, submerge and wait. If it's a "T" then you have to be careful of where you will intercept.
Anyways, there is no way you can catch up to a TF if it's going 19+ knots!
