Heave to, and Prepare to be Boarded!

“If you want to learn a new idea, read an old book.” —Attributed to Ivan Pavlov

Recent maritime interdiction operations have been conducted primarily as part of antipiracy efforts or enforcement of U.N. Security Council resolutions. But during interstate armed conflict—declared or existing in fact—belligerents are entitled to capture civilian enemy vessels (and neutral vessels that support the adversary) for the use and benefit of the captor nation. This right, known as taking of prize, has lain dormant in U.S. practice for more than a century. While other authors have thoughtfully opined on the utility of disrupting an adversary’s economy as a tactic of war, the legal and material practicalities of exercising this belligerent right have not been robustly examined or updated.¹ Nonetheless, its exercise remains legal, and as the Navy prepares all available tools for competition and possible conflict, it is worth dusting off writings on prize law’s history and application to reconsider it for contemporary use.

During armed conflict, civilian ships of enemy nationality and neutral vessels carrying contraband—as distinguished from enemy warships or neutral ships engaged in hostilities—are subject to lawful seizure through a formal legal process under prize law. Both international law and the domestic law of many nations, including the United States, provide for adjudication of prize cases to transfer title of captured ships and their cargoes to the capturing state. The vessel and its cargo may be judicially “condemned” as a prize only once that process is complete. This ensures the lawful transfer of prizes by providing for a standardized and legitimate process to consider evidence that vessels were appropriate subjects of seizure and protect the rights of all parties. The prize court process also distinguishes lawful belligerent seizure from piracy, an international crime defined as illegal depredation committed for private ends by private ships or aircraft against other ships or aircraft.²

A Brief History of Prize Law

Prize law evolved over centuries, with progressive formalization of the customary practice of capturing enemy property, including ships, cargo, and neutral ships supporting the adversary.³ The concept traces back to medieval maritime customs, when capturing enemy vessels and their cargoes was understood first as a form of equitable relief between states below the level of war, and later as a legitimate means of weakening an adversary during conflict. In the early 17th century, Hugo Grotius, a legal scholar famous for his early contributions to the field of international law, wrote extensively on the law of war. One of his first works, De Jure Praedae (On the Law of Prize and Booty), laid the foundation for formally recognizing the legality of capturing enemy prizes.⁴

In the mid-19th century, nations began to codify and regulate the law of maritime warfare. The Paris Declaration Respecting Maritime Law of 1856, signed by major powers including the United Kingdom, France, and Russia, sought to abolish privateering, the practice of giving private individuals or ships letters of marque that authorized them to seize enemy vessels for profit during armed conflict. While the United States did not sign this treaty, it has adhered to many of its principles since the early 1900s, including the prohibition on privateering. The Hague Conventions of the late 19th and early 20th centuries included provisions on the treatment of captured prizes during naval warfare to ensure procedural agreement among states and attempted to set up an international prize court.⁵

Although the practice of taking prizes decreased after World War I, the right continues to exist in international law, and many states continue to maintain the legal infrastructure required to execute the practice. After World War II, many states comprehensively reevaluated the balance of belligerent rights with protection of neutrals and humanitarian considerations. The resulting legal framework—including the United Nations Charter, the 1949 Geneva Conventions, the 1958 Geneva Conventions on the High Seas, and the United Nations Convention on the Law of the Sea—changed many elements of customary naval operations, but prize law remained intact. To this day, scholars of international humanitarian law and the Law of Armed Conflict acknowledge its lawfulness and availability as a tool of war.⁶

U.S. Prize Law

From its very beginnings, the United States has recognized and codified the right to take prizes in war. Throughout American history, prize courts have been established and operated as necessary during armed conflict. As early as 1775, the Colony of Massachusetts established prize courts to adjudicate captures at sea. In 1780, the Continental Congress established the first American prize courts to consider appeals from the Courts of Admiralty in cases of capture.⁷ These courts were tasked with adjudicating the legality of captured prizes, ensuring those captures adhered to the rules of war, and providing nonbelligerents with recourse if their property was captured or destroyed illegally.

Further, the drafters of the U.S. Constitution recognized the critical importance of this belligerent right and codified the authority of Congress to establish prize courts in Article I, section 8. This grants Congress the power to “define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations,” and to “make rules concerning Captures on Land and Water.” By the War of 1812, prize courts had been established in the new nation to handle captured enemy vessels and property.⁸

During the American Civil War (1861–65), both the Union and Confederacy established prize courts to adjudicate the legality of captures at sea and determine how to distribute seized assets.⁹ The most famous U.S. Supreme Court case on the subject, appropriately referred to as The Prize Cases, 67 US 635 (1863), held the seizure of ships running a blockade of Southern ports was lawful because a state of war existed in fact between the Union and Confederacy, even though Congress had not formally declared war. Similarly, the Supreme Court case Mrs. Alexander’s Cotton, 69 U.S. 404 (1864), recognized the right of the Union to capture cargo as a prize, again owing to the existence of a war in fact. In U.S. law, the right to take prizes during armed conflict therefore exists irrespective of a formal declaration of war.

The 1898 Spanish-American War gave rise to the Manila Prize Cases, 188 U.S. 254 (1903), which involved the legality of the seizure and condemnation of vessels that had been detained by the U.S. Navy in Manila Bay, Philippines. The primary issue in these cases was whether the vessels and their cargoes captured abroad were lawfully captured as prizes of war. In its holding, the Supreme Court recognized the existence of a state of war between the United States and Spain and determined that the seizure of Spanish-owned vessels was therefore legitimate. Important, the Manila Prize Cases recognized that the capture of vessels in territory that was not contiguous to the United States was still lawful, thereby recognizing the U.S. Navy’s authority to capture prizes under U.S. and international law anywhere in the global maritime commons.

U.S. forces brought no cases before U.S. prize courts in either World War I or World War II. But that did not mean prize law in the United States or elsewhere stopped evolving and maturing. The United States, United Kingdom, Austria-Hungary, China, France, Belgium, Italy, Japan, Germany, and other belligerents established and refined their prize court processes as World War I unfolded.¹⁰ The Supreme Court adjudicated The Steamship Appam, 243 U.S. 124 (1917), in which it held in favor of the British owners of a vessel captured by the German Navy and brought into a U.S. court for a prize proceeding. The Supreme Court applied customary international law in concluding that a belligerent nation may not bring a prize case in a neutral port, which the United States was at that time. Similarly, the United States and other belligerents issued new legislation allowing prize proceedings during World War II, and their courts began to interpret traditional principles to apply to modern conditions.¹¹

After World War II, Congress passed laws to ensure the U.S. military could continue to lawfully capture and condemn prizes.¹² And though no U.S. courts have heard prize cases since these statutes were adopted in the 1950s, Congress has updated the prize statutes at least three times since then, most recently in 2021 to include a provision about the U.S. Space Force, demonstrating Congress’s intent that prize law remain available and in effect. Indeed, the latest version of the U.S. Navy’s Commander’s Handbook on the Law of Naval Operations acknowledges the role prize courts must play in modern conflict, indicating prize law’s operational importance.¹³

Away All Boarders!

To ensure the Navy is prepared to present U.S. decision-makers with all appropriate tools during a conflict, Navy warfighters, policy-makers, and judge advocates will continue to update the legal and procedural steps required to operate under prize law. The Newport Manual on the Law of Naval Warfare includes detailed coverage of the subject, but recent academic thought has conflicting perspectives about the exercise of what is often termed “economic warfare” during modern conflict.¹⁴

To facilitate smooth exercise of prize law in the event of conflict and ensure a practice that protects and upholds neutral global maritime commerce, the process within and among the U.S. armed forces and justice system must be updated, and legal consensus must be built ahead of time with allies and partners. Work so far has identified areas of federal law to update to modern procedural and evidentiary standards, as well as Navy manuals to correct and disseminate. From here, interagency work will focus on creating guidelines for designating, standing up, and manning prize courts. Similarly, work with allies and partners will focus on rules for interoperability, interdiction, and evidentiary and disposition processes. Finally, both military personnel and their attorneys must be educated and trained on prize law, its lawful place in maritime conflict, and how their roles intersect with and support operations and court proceedings.

Constricting the flow of enemy matériel, preventing movement of contraband, and degrading enemy sealift are essential components of interstate maritime warfare. Describing these efforts as “piracy” or as undermining global maritime trade would be mistaken, and it would ignore the long history and careful balance struck in the law of war between neutral and belligerent rights. Alfred Thayer Mahan, one of the most important modern thinkers on naval warfare, illuminated the critical overlap between naval might and the economic security of the nation.¹⁵ In conflicts among major powers, the ability to degrade the adversary’s economic production has been seen as a consistent aspect of victory. The lawful, rules-based right of belligerents to directly seize as prizes shipping and cargo, and thus diminish enemy economic power at sea, is an idea new to many leaders today, but it is firmly rooted in many old books.