If you really want the realism, just build a SACF/IS-WAS. That will let you calculate the AOB and speed you need to enter into the TDC (you'll alread have range and bearing).
It isn't that hard, it's basically just two circular slide rules back to back, and there are the original instructions on how to use it at the HNSA website.
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The U-Boat Commander of Love
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