In case of a private vessel the flag is a common evidence, but in case of doubt the vessel must show to proper authorities its papers which certify its nationality.
(c) The general exercise of jurisdiction over vessels is as follows:—
(1) Upon the high seas and within its own waters the jurisdiction of a state over its public and private vessels is exclusive for all cases.
(2) Over public vessels in foreign waters, the jurisdiction of the state to which a public vessel belongs is exclusive for all matters of internal economy. The vessels are subject to port regulations in matters of anchorage, public safety, etc. As Dana says in his note to Wheaton, "It may be considered as established law, now, that the public vessels of a foreign state coming within the jurisdiction of a friendly state, are exempt from all forms of process in private suits."[150] In general practice the waters of all states are open to the vessels of war of all other states with which they are at peace. This is a matter of courtesy and not of right, and is in fact sometimes denied, as by the provision of the Treaty of Berlin, 1878, "The port of Antivari and all the waters of Montenegro shall remain closed to the ships of war of all nations."[151] Various regulations may require, without offence, notice of arrival, probable duration of stay, rank of commander, etc.
The boats, rafts, etc., attached to a vessel of war are regarded as a part of the ship while engaged in the public service.
While there is some difference of opinion as to the immunities of the persons belonging to a ship of war in a foreign harbor, a generally admitted rule seems to be that while the persons of a ship of war are engaged in any public service that is not prohibited by the local authorities, such persons are exempt from local jurisdiction. The ship's crew would not be arrested and detained by local authorities for minor breaches of local regulations, though they might be sent on board their vessel with statement of reasons for such action. If the action of the crew constitutes a violation of the law of the country to which they belong, the commander of the ship may punish them, and report his action to the local authorities. In case of crimes of serious nature the commander may turn the offenders over to the local authorities, but must assure them a fair trial.
The commander of a vessel is, of course, always responsible to his home government, and his action may become the subject of diplomatic negotiations.
The question of right of asylum on board a ship of war has been much discussed. First, Most civilized states now afford asylum on board their ships of war to those who, in the less civilized regions, flee from slavery.[152] Second, In cases of revolution ships of war sometimes afford refuge to members of the defeated party, though the ship of war may not be used as a safe point from which further hostilities may be undertaken. Third, A commander may afford asylum to political refugees under circumstances which he thinks advisable. Fourth, In cases where asylum is granted to offenders whether political, or (in case of treaty right) criminal, if the request of the local authorities for the release of the criminal is refused by the commander of the ship, there is no recourse except to the diplomatic channels through extradition.
The immunities granted to vessels of war are also generally conceded to other vessels strictly upon public service, e.g. carrying an ambassador to his post. The largest possible exemption is given to a vessel conveying the sovereign of a state. Vessels transporting military forces in command of regularly commissioned government officers are usually granted immunities accorded to men-of-war.