The actual investment of a port or place by a hostile force fully competent to cut off all communication therewith, so arranged or disposed as to be able to apply its force to every point of practicable access or approach to the port or place so invested.
It is proper here to consider, 1. by what authority a blockade can be established; 2. what force is sufficient to constitute a blockade; 3. the consequences of a violation of the blockade.
Natural sovereignty confers the right of declaring war and the right which nations at war have of destroying or capturing each other's citizens, subjects or goods, imposes on neutral nations the obligation not to interfere with the exercise of this right within the rules prescribed by the law of nations. A declaration of a siege or blockade is an act of sovereignty, but a direct declaration by the sovereign authority of the besieging belligerent is not always requisite; particularly when the blockade is on a distant station; for its officers may have power, either expressly or by implication, to institute such siege or blockade.
To be sufficient the blockade must be effective and made known. By the convention of the Baltic powers of 1780, and again in 1801, and by the ordinance of congress of 1781, it is required there should be a number of vessels stationed near enough to the port to make the entry apparently dangerous. The government of the United States has uniformly insisted that the blockade should be effective by the presence of a competent force, stationed and present, at or near the entrance of the port. But 'it is not an accidental absence of the blockading force, nor the circumstance of being blown off by wind, (if the suspension and the-reason of the suspension are known,) that will be sufficient in law to remove a blockade.' But negligence or remissness on the part of the cruizers stationed to maintain the blockade, may excuse persons, under circumstances, for violating the blockade. To involve a neutral in the consequences of violating a blockade it is indispensable that he should have due notice of it: this information may be communicated to him in two ways; either actually, by a formal notice from the blockading power, or constructively by notice to his government, or by the notoriety of the fact.
In considering the consequences of the violation of a blockade it is proper to take a view of what will amount to such a violation, and, then, of its effects. As all criminal acts require an intention to commit them, the party must intend to violate the blockade or his acts will be perfectly innocent; but this intention will be judged of by the circumstances. This violation may be either by going into the place blockaded or by coming out of it with a cargo laden after the commencement of the blockade. Also placing himself so near a blockaded port as to be in a condition to slip in without observation is a violation of the blockade and raises the presumption of a criminal intent. The sailing for a blockaded port, knowing it to be blockaded, is it seems, such an act as may charge the party with a breach of the blockade. When the ship has contracted guilt by a breach of the blockade, she may be taken at any time before the end of her voyage, but the penalty travels no further than the end of her return voyage. When taken, the ship is confiscated and the cargo is always, prima facie, implicated in the guilt of the owner or master of the ship and the burden of rebutting the presumption that the vessel was going in for the benefit of the cargo, and with the direction of the owners, rests with them.