Thomas Barclay

“ This became gradually the recognized view, and when in 1856 the powers represented at the congress of Paris inserted in the declaration there adopted that “blockades in order to be binding must be effective, that is to say, maintained by a force sufficient really to prevent access to the coast of an enemy,” they were merely enunciating a rule which neutral states had already become too powerful to allow belligerents to disregard.
Blockade is universally admitted to be a belligerent right to which under international law neutrals are obliged to submit. ”

“ It is now also universally admitted that the above-quoted rule of the Declaration of Paris forms part of international law, independently of the declaration. Being, however, exclusively a belligerent right, it cannot be exercised except by a belligerent force. Even a de facto belligerent has the right to institute a blockade binding on neutrals if it has the means of making it effective, though the force opposed to it may treat the de facto belligerent as rebels. ”

“ With the employment in warfare of larger vessels in the place of the more numerous small ones of an earlier age, notice, moreover, would tend to take the place of de facto investment, and at a time when communication between governments was still slow and precarious, such notice would sometimes be given as a possible measure of belligerent tactics before the blockade could be actually carried out. ”