AOB is the degree angle that the target ship sees you (if he could).
Take the protractor, click somewhere on the target course (ahead of target)
Second, click on the target (this is the anchor point)
Third, click the last point of the protractor on your sub.
The angle is shows is your AOB. If the line connecting the target to your sub is on the target's port side, then it's AOB port and vice versa.
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