Judging by the 1775 date and early US flag I'd say it's American War of Independence related item. Possibly connected to Battle of Bunker Hill 1775? What makes you think it's an "antique" rather than a recently made item?
Medal for Military Achievement: FOR MILITARY ACHIEVEMENT Medal & Blue Ribbon 1775 ARMY - FREE SHIP | eBay
It is the US Army Achievement Medal. First authorized in 1981. It's the lowest medal in precedence as I recall. The design on the obverse comes from the Department of the Army seal and emblem.