Ex parte Atocha was a United States Supreme Court case that dealt with the issue of whether a foreign vessel could be seized by a U.S. court for a debt owed by its owners. The case involved the Spanish vessel Atocha, which was owned by a Spanish company. The company had defaulted on a loan from a U.S. citizen, and the creditor sought to have the vessel seized in order to satisfy the debt. The Supreme Court held that the vessel could not be seized, as it was a foreign vessel and the U.S. court did not have jurisdiction over it. The Court reasoned that the vessel was not subject to the jurisdiction of the U.S. court, and that the creditor could not use the court to enforce a foreign debt. The Court also noted that the vessel was not within the territorial jurisdiction of the U.S. court, and that the creditor could not use the court to enforce a foreign debt. The Court's decision was based on the principle of comity, which is the recognition of the laws and judicial decisions of foreign nations. The Court held that the U.S. court could not interfere with the rights of a foreign nation, and that the creditor could not use the court to enforce a foreign debt.

In Ex Parte Atocha, the Supreme Court was asked to decide whether a Spanish vessel that had been abandoned by its crew during the Civil War could be considered an enemy ship. The majority opinion held that it could not because there was no evidence of any hostile act or intent on behalf of Spain towards the United States. However, in his dissenting opinion Justice Field argued that even if there were no direct acts of hostility from Spain against the United States, this did not mean that they should be exempt from being classified as an enemy ship. He reasoned that since Spain had declared war on both sides in the conflict and provided aid to one side over another, their neutrality should not protect them from being labeled as enemies under international law. Furthermore, he stated that even though there may have been some ambiguity surrounding which nation owned and operated the vessel at issue here, such uncertainty should never excuse a belligerent party from having their ships treated as enemies when captured by opposing forces.