Admiral William T. Sampson, who commanded the blockade, justified the seizures by stating that most fishing vessels flying under the Spanish banner were manned by well trained seamen with prior naval experience who could be called up to fight for Spain.

[3] The Court cited lengthy legal precedents in support of this conclusion, which it described as an "ancient usage among civilized nations, beginning centuries ago, and gradually ripening into a rule of international law.

Similarly, in 1521, a treaty between Emperor Charles V of the Holy Roman Empire and Francis I of France exempted fishing vessels from capture, on the basis that both nations would face widespread hunger if fishermen did not feel safe to set sail.

Justice Gray also relied on the theories and opinions of contemporary jurists and commentators from across the world to buttress the Court's reasoning, decades before such scholarly legal work would be codified as a primary source of international law:[A]t the present day, by the general consent of the civilized nations of the world, and independently of any express treaty or other public act, it is an established rule of international law, founded on considerations of humanity... and of the mutual convenience of belligerent states, that coast fishing vessels, with their implements and supplies, cargoes and crews, unarmed and honestly pursuing their peaceful calling of catching and bringing in fresh fish, are exempt from capture as prize of war.

For this purpose, where there is no treaty and no controlling executive or legislative act or judicial decision, resort must be had to the customs and usages of civilized nations, and, as evidence of these, to the works of jurists and commentators who by years of labor, research, and experience have made themselves peculiarly well acquainted with the subjects of which they treat.

[7] Fuller essentially agreed with the federal government's position and argued that the capture of fishing vessels as prizes had been in accordance with both customary international law and militarily necessary and that any exemption is under the discretion of the President as the nation's executive.