The world being composed of distinct sovereignties, possessing equal rights and equal independence, whose mutual benefit is promoted by intercourse … have consented to a relaxation in practice, in cases under certain peculiar circumstances, of that absolute and complete jurisdiction
One sovereign being in no respect amenable to another, and being bound by obligations of the highest character not to degrade the dignity 1 [bases of immunity] of his nation, by placing himself or his sovereign rights within the jurisdiction of another, can be supposed to enter a foreign territory only under an express licence or in the confidence that the immunities belonging to his independent sovereign station, though not expressly stipulated, are reserved by implication, an will be extended to him.
This perfect equality 2 and absolute independence 3 of sovereigns, and this common interest impelling them to mutual intercourse, and an interchange of good offices with each other, [comity and reciprocity 4], have given rise to a class of cases in which every sovereign is understood to waive [of local sovereign 5] the exercise of a part of that complete exclusive territorial jurisdiction, which has been stated to be the attribute of every nation.
Why has the whole civilizes world concurred in this constructions? The answer cannot be a mistaken. A foreign sovereign is not understood as intending to subject himself to a jurisdiction incompatible with its dignity
‘it is impossible to conceive,’ says Vattel, ‘that a Prince who sends an ambassador or any other minister can have any intention of subjecting him to the authority of a foreign power … the latter, in receiving the minister, consents to admit him on the footing of independency’
As a public armed shipped acts under the immediate and direct command of a sovereign, the vessel was exempt from US jurisdiction.