So.... turns out the Minutemen Castle is pretty cool for another reason. Artillery strikes. Once you retake the castle, get past Sarge in the tunnels, and access the armory, you gain the ability to call in artillery strikes that rain down heavy artillery from the sky. Serious boom. And then you can place artillery cannons at any settlement you have, and be able to call in airstrikes from that settlement too. Haven't figured out exactly what the range is, but it's pretty far. With enough settlements, you could blanket the map.
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