For some reason, for two nights in a row, helicopters have circled the financial district in Boston. My hotel was directly under their flight path, so for an hour, the windows rattled every time they passed in the dark.
The porter told me it was some sort of military training, but I’m not sure about this… the closest airforce base to Boston is Hanscom Air Force Base, who don’t appear to have helicopters but do work with the Joint Base Cape Cod, a training facility for both the Coast Guard and the National Guard. This is an hour and a half away from Boston (driving).
If these came from Joint Base Cape Cod, these were likely Jayhawk helicopters. It’s hard to say because it was so dark.