territorial principle

the criminal jurisdiction of the United States is in general based on the territorial principle, and criminal statutes of the United States are not by implication given an extraterritorial effect; but that principle has never been thought to be applicable to a merchant vessel which, for purposes of the jurisdiction of the courts of the sovereignty whose flag it flies to punish crimes committed upon it, is deemed to be a part of the territory of that sovereignty, and not to lose that character when in navigable waters within the territorial limits of another sovereignty