Definition
A ruse de guerre (from French: "trick of war") is a deliberate deception or stratagem employed in armed conflict to mislead an enemy. Under the laws of war, ruses de guerre are lawful methods of warfare — acts intended to confuse, mislead, or induce a mistaken belief in the opposing force — so long as they do not violate the rules and customs of international armed conflict.
The concept is distinguished from perfidy, which is the unlawful invocation of protected status to kill, injure, or capture. A ruse deceives without invoking legal protections to which the deceiver is not entitled. Feigning a false position, using camouflage, conducting a feint attack, or broadcasting disinformation about troop movements are classic examples of lawful ruses. Feigning surrender while preparing to resume fire, or using enemy uniforms to conduct a hostile attack, crosses into perfidy and is prohibited.
Common Language
Modern common usage (Wiktionary): "A stratagem of war."
The common and legal meanings are closely aligned here, but the legal term carries a formal normative dimension that the plain definition omits. In international humanitarian law, ruse de guerre is a term of art that does legal work: it marks the boundary between permitted deception and prohibited perfidy. The common definition says nothing about this boundary, making it incomplete for any legal research purpose.
Common Confusion
Ruse de guerre is frequently confused with perfidy. The distinction is operationally and legally significant. Both involve deception in armed conflict, but perfidy specifically exploits protections afforded by the laws of war — flags of truce, the red cross emblem, feigned incapacitation, or feigned surrender — to gain a military advantage. A ruse de guerre exploits the enemy's ignorance or confusion without abusing a protected status. The legal consequence is stark: perfidy constitutes a war crime; a ruse de guerre does not. Researchers encountering historical tribunal records, military manuals, or international law commentary must take care not to treat all battlefield deception as a single undifferentiated category.
Why It Matters in Research
The term appears infrequently in domestic legal sources and almost exclusively in the context of the laws of armed conflict, military manuals, international tribunal proceedings, and treatises on international humanitarian law. Researchers working in the Law Mind corpus should anticipate that ruse de guerre will surface primarily in materials touching on the Hague Conventions, the Geneva Conventions and their Additional Protocols, war crimes proceedings, and military doctrine rather than in domestic case law or statutes.
The codification of the ruse/perfidy distinction is relatively modern in explicit form. The 1907 Hague Regulations (Articles 23–24) addressed permissible ruses without fully articulating the distinction. The Additional Protocol I to the Geneva Conventions (1977) sharpened the boundary at Article 37 (prohibiting perfidy) and Article 39 (prohibiting misuse of emblems), giving the ruse de guerre concept its clearest contemporary legal footing. Historical sources predating 1977 will treat the concept less precisely, and researchers should read them with that evolution in mind.
A secondary trap: in older military and legal writing, "stratagem" is used loosely and may encompass acts that modern law would classify as perfidy. Do not assume that historical approval of a "stratagem" or "ruse" reflects contemporary legal permissibility.
Historical Dictionary Support
Both Black's Law Dictionary editions define ruse de guerre simply as "a trick in war; a stratagem." This is accurate as a translation and useful as an entry point, but neither edition does any legal work with the term. Neither source engages the ruse/perfidy distinction, the Hague framework, or any normative dimension. The brevity is unsurprising — domestic American legal dictionaries of those periods had limited occasion to develop international humanitarian law concepts in depth.
Historical legal dictionaries are largely silent on the internal legal framework governing when a ruse is lawful. Researchers should treat the Black's entries as confirmation of the term's meaning and provenance, not as substantive guidance on its legal content. For that, the relevant sources are international treaties, military manuals (including the U.S. Army Field Manual on the Law of Land Warfare), and commentary from authorities such as Oppenheim's International Law and the ICRC Commentaries.
Jurisdictional Note
The rules governing ruse de guerre are creatures of international law rather than any domestic legal system. Domestic courts have limited occasion to apply the concept directly. Application is primarily through international tribunal proceedings (including the International Criminal Court and ad hoc tribunals), military court-martial proceedings under the law of war, and executive-branch military doctrine.