1. Get target's course through your observations
2. Chose a bearing that you will fire at the target on
3. Draw a line from your sub along your chosen bearing so that it intersects with target's course
4. Measure that angle with the protractor. This will be the aob when the target reaches your firing bearing.
5. Enter AOB manually
6. When the target reaches the bearing you have chosen, fire!
If you want to target specific parts of the ship, then set your periscope for your "firing bearing" and wait until the section you want to hit enters your crosshairs.
