The United States v. Ship Helen was a Supreme Court case in which the government sought to recover damages from the ship's owners for violating an embargo imposed by President Thomas Jefferson in 1807. The court held that, under international law, ships are subject to forfeiture if they violate embargoes or other restrictions on trade and commerce. Furthermore, it found that such forfeitures could be enforced even when the owner of a vessel is unaware of any violation committed by their vessel; ignorance does not excuse liability for violations of this nature. Ultimately, the court ruled against Ship Helen’s owners and ordered them to pay restitution for their breach of embargo laws. This ruling established precedent regarding how governments can enforce embargoes and other restrictions on foreign trade through civil penalties levied against vessels owned by private citizens who may have been ignorant about any wrongdoing committed by their vessels while abroad.

In the case of The United States v. Ship Helen, a majority opinion was issued by Chief Justice Marshall that held the vessel and its cargo liable to forfeiture for having been used in violation of an act of Congress prohibiting trade with France. However, Justice Johnson dissented from this decision on two grounds: firstly, he argued that there was no evidence presented at trial showing any knowledge or intent on behalf of the owner or master to violate the law; secondly, he contended that even if such knowledge had been shown it would not be sufficient to justify forfeiture as punishment since it is only applicable when expressly provided for by statute. He concluded his dissent by stating that “the power which punishes without proof should never be exercised unless clearly given” and thus urged caution against allowing government agencies too much discretion in their enforcement activities.