The following are Congressional Research Service Legal Sidebar reports, Letters of Marque and Reprisal: Introduction and Historical Context and Drafting History and U.S. Practice.
From the report
Letters of marque and reprisal were once common tools for countries with small naval forces to augment their militaries by drawing upon the strength of their private merchant vessels. As a young country, the United States used the instruments with success in several early conflicts, including the Revolutionary War and the War of 1812. Over the course of the 19th century, however, commissioning private parties to use armed force fell out of favor in domestic and international practice, and Congress has not authorized a President to issue the instruments since the Civil War. (See CRS Legal Sidebar LSB11273, Letters of Marque and Reprisal (Part 2): Drafting History and U.S. Practice.)
During the era when the United States used letters of marque and reprisal, Congress historically authorized the President to issue the instruments, subject to statutorily defined requirements and conditions, rather than issue instruments directly from the legislative branch. Individual states, by contrast, are prohibited from issuing the instruments under Article I, Section 10 of the Constitution.
The Framers of the Constitution placed the Marque and Reprisal Clause between provisions that authorize Congress to declare war and to “make Rules concerning Captures on Land and Water.” These three authorities are interrelated and can function together. For instance, in conjunction with declaring war, Congress might authorize letters of marque and reprisal allowing private ship-owners to assist the war effort by targeting enemy vessels, as it did in the War of 1812. Holders of those letters could then capture enemy vessels and bring them into port to be condemned and sold as prizes of war. Using its authority to:
“make Rules concerning Captures[,]” Congress could define the legal framework governing how the condemnation proceedings would operate and how the proceeds of the sale would be distributed.
The Supreme Court has mentioned the Marque and Reprisal Clause most frequently when listing Congress’s war powers and authorities over foreign affairs. The Court has described the power to issue letters of marque and reprisal as an inherent feature of sovereignty that is national in nature. The Court has further observed that the Constitution expressly grants Congress the power to issue the instruments and that “no restrictions are imposed” upon that authority. Finally, in an opinion for the Court in Barron v. City of Baltimore, Chief Justice John Marshall observed that the Constitution grants power over the instruments to the federal government while denying states the ability to issue them because, “[t]o grant letters of marque and reprisal, would lead directly to war; the power of declaring which is expressly given to congress.”
