I always thought the best way to explain was with the flashlight: Imagine a guy standing on the bridge of the target vessel. He holds one flashlight directly in direction of the bow, i.e. the course his ship is heading. The other flashlight he points at your submarine.
The angle between those two beams of lights is the AoB.
If the ship is heading away from you (i.e. the AoB is greater than 90°), you from 180 subtract the AoB. (Effectively the guy with the flashlight would stand at the stern)
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= CRY PTO = MITSH VBHIZ OSMWG OECEY MLZTO UMDFV TKORD B
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