Used as a warning system in the old north church (describe it in one word)

Built in 1723 and oldest standing church in Boston.

In the Old North Church of Boston one lantern would be lit if the British were coming by land and two of them lit if they were to come by sea.
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One word I would use to describe this is "tactical" or "strategic."
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Didn't really understand what you were asking, but I hope this helped somewhat.

Idgaf answer yourselve u bum