The Sea Lion was a case heard by the United States Supreme Court in 1866. The case revolved around the question of whether or not an American citizen could be held liable for damages caused by their vessel while navigating foreign waters. At issue was whether or not a shipowner, who had been sued in California state court for damages to another vessel that occurred during navigation off the coast of Mexico, could be held liable under US law. In its decision, the Supreme Court ruled that although it is generally accepted that vessels are subject to local laws when operating on foreign seas and oceans, this does not extend to civil liability claims brought against them in US courts. As such, they found that no actionable claim existed against the owner of The Sea Lion and dismissed all charges against him.

In The Sea Lion, the Supreme Court was asked to decide whether a foreign vessel that had been seized by U.S. authorities for violating neutrality laws could be held in custody until the end of hostilities between two other countries. In a dissenting opinion, Justice Field argued that such an action would violate international law and deprive the owner of his property without due process of law. He noted that while Congress has broad powers over matters concerning war and peace, it does not have authority to seize private vessels or interfere with neutral commerce during peacetime unless authorized by treaty or statute. Furthermore, he argued that even if Congress did possess this power under certain circumstances, it should not be exercised here because there is no evidence showing any danger posed by allowing the vessel to remain at sea during wartime hostilities between two other nations.