The Portsmouth was a case heard by the United States Supreme Court in 1869. The case involved a dispute between the owners of the Portsmouth, a steamship, and the United States government. The government had seized the Portsmouth for alleged violations of the Neutrality Act of 1794. The owners of the Portsmouth argued that the government had no right to seize the vessel without due process of law. The Supreme Court ruled in favor of the owners of the Portsmouth. The Court held that the government had violated the Fifth Amendment of the Constitution, which guarantees due process of law. The Court also held that the government had violated the Neutrality Act of 1794, which prohibited the seizure of vessels without due process of law. The Portsmouth case was an important decision in the development of constitutional law. It established the principle that the government must provide due process of law before seizing a vessel. This principle has been applied in numerous cases since then, and it remains an important part of constitutional law today.

In the case of The Portsmouth, Justice Field wrote a dissenting opinion arguing that Congress had no authority to pass legislation allowing for the sale of public vessels. He argued that such an action was beyond their power and would be unconstitutional as it violated Article I, Section 8 of the Constitution which grants Congress exclusive control over naval forces. Furthermore, he argued that if this law were allowed to stand then it could set a dangerous precedent whereby any branch of government could dispose of its property without proper authorization from Congress or other branches. In conclusion, Justice Field believed that while there may have been good intentions behind this law they did not outweigh its potential implications and thus should not be allowed to stand.