The Grapeshot was a Supreme Court case that dealt with the issue of whether a state could tax a federal vessel. The case was brought by the United States against the State of Louisiana. The United States argued that the state had no authority to tax a federal vessel, as it was a violation of the Supremacy Clause of the Constitution. The Supreme Court agreed with the United States, ruling that the state had no authority to tax a federal vessel. The Court reasoned that the Supremacy Clause of the Constitution gave the federal government exclusive authority over matters of national concern, such as taxation of federal vessels. The Court also noted that the state had no authority to interfere with the federal government's power to regulate commerce. The Court concluded that the state's attempt to tax a federal vessel was unconstitutional and therefore invalid. The Grapeshot case was an important decision in the development of the federal government's power to regulate commerce. It established that the federal government had exclusive authority over matters of national concern, such as taxation of federal vessels. The decision also established that the states could not interfere with the federal government's power to regulate commerce.

In The Grapeshot case, the Supreme Court was asked to decide whether a vessel that had been seized by Confederate forces during the Civil War could be considered an enemy ship. The majority opinion held that it was not an enemy ship because it had been taken over by private individuals and not by any government or military force. However, in his dissenting opinion Justice Field argued that since the vessel had been taken over for use as a warship against Union forces, it should be treated as such and thus classified as an enemy ship. He further argued that even if no formal declaration of war existed between the two sides at the time of seizure, this did not change its status as an enemy vessel since hostilities were already underway when it was captured. In conclusion, Justice Field believed that regardless of who actually took possession of the vessel after capture, its purpose remained unchanged - to fight against Union forces - and therefore should be deemed an enemy ship under international law.