The Merrimack was a case heard by the United States Supreme Court in 1814. The case involved two vessels, the Merrimack and the Eliza Ann, which were both owned by William Brown of Massachusetts. Brown had sent his vessel, the Eliza Ann to sea with instructions to trade goods for money or other merchandise. However, while at sea it encountered a French privateer called La Jeune Eugenie that seized it and took its cargo as prize. When news of this reached Brown he filed suit against La Jeune Eugenie's owners claiming damages for their seizure of his ship and cargo without just cause or provocation. In response to this claim, La Jeune Eugenie's owners argued that they acted within their rights under international law since France was then at war with Great Britain (of which Massachusetts was part). The court ultimately sided with Brown ruling that even though France may have been legally justified in seizing British ships during wartime such actions could not be taken against neutral American vessels like those belonging to William Brown who had no connection whatsoever with either belligerent nation.

In The Merrimack, the Supreme Court was tasked with deciding whether a vessel that had been captured during wartime could be considered an enemy ship and therefore subject to condemnation. Justice Johnson wrote the dissenting opinion in which he argued that Congress did not have the power to condemn vessels of neutral nations as enemies without first obtaining their consent. He further argued that if such a practice were allowed, it would lead to "the most serious consequences" for all nations involved in international trade. Furthermore, Johnson contended that since there was no evidence of any hostile intent on behalf of either nation at issue in this case, it should not be assumed they were enemies simply because one country declared war against another. In conclusion, Justice Johnson believed Congress lacked authority to condemn vessels belonging to neutral countries without their permission and thus concluded his dissent from the majority opinion.