...can we have a clue?
...so far, it's a military installation (but not a fort) in a town nearish boston, not on an island, that is related to the civil war and didn't exist ("surprisingly"you said) during the revolutionary war. You said it has historical significance "in a sense"
...does it start with an F ? (not trying to be a smart aleck...lol...i just recall reading about a Camp Farmington or something that sounds like that where training occurred for volunteer soldiers)
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