Prohibition of Perfidy

The prohibition of perfidy is a foundational rule of international humanitarian law (IHL) that forbids combatants from betraying an adversary's confidence in legal protections in order to kill, injure, or capture them. Its modern treaty basis is Article 37(1) of Additional Protocol I (AP I) of 1977 to the Geneva Conventions, which defines perfidy as "acts inviting the confidence of an adversary to lead him to believe that he is entitled to, or is obliged to accord, protection under the rules of international law applicable in armed conflict, with intent to betray that confidence." The rule has deep customary roots predating its codification: Article 23(b) of the 1907 Hague Regulations prohibited treacherously killing or wounding individuals belonging to the hostile nation, and the 1863 Lieber Code (Article 16) condemned acts of perfidy as incompatible with the laws of war. The International Committee of the Red Cross (ICRC) lists the prohibition as Rule 65 of its Customary IHL Study, binding in both international and non-international armed conflict.

The mechanics of perfidy turn on a two-element test. First, the perpetrator must invite the adversary's confidence that a legal protection applies — for example, by displaying a white flag of truce, feigning surrender, simulating incapacitation by wounds, or wearing the distinctive emblem of the red cross or red crescent. Second, the perpetrator must act with intent to betray that confidence, and the betrayal must result in killing, injuring, or capturing the enemy. Both elements are essential: the deception alone is not perfidy unless it is the operative means by which the protected status is exploited to commit a hostile act. Article 37(1) enumerates illustrative examples, including the feigning of surrender, of an intent to negotiate under a flag of truce, of incapacitation by wounds or sickness, of civilian or non-combatant status, and of protected status by using the emblems or uniforms of the United Nations or of neutral States not party to the conflict.

A central distinction within the regime is the threshold of harm. Article 37 perfidy is consummated only when the betrayal kills, injures, or captures. A separate and broader prohibition addresses the improper use of emblems and signs as such: Article 38 of AP I bars improper use of the red cross, red crescent, and other recognized protective emblems and the distinctive emblem of the United Nations, and Article 39 prohibits the use of enemy flags, military emblems, insignia, or uniforms while engaging in attacks or to shield military operations. These provisions criminalize the misuse regardless of resulting casualties, whereas perfidy proper requires the lethal or capturing outcome. The Statute of the International Criminal Court reflects this in Article 8(2)(b)(xi) and (vii), which list treacherously killing or wounding and the improper use of protective emblems among war crimes.

Contemporary practice illustrates the rule's continuing relevance. Military manuals of the United States Department of Defense (the 2015 Law of War Manual), the United Kingdom Ministry of Defence (JSP 383, 2004), and Germany's Bundesministerium der Verteidigung all reproduce the perfidy prohibition and cite the surrender and red-cross-emblem scenarios. Allegations of perfidy have recurred in modern conflicts: combatants feigning surrender to ambush approaching forces, the use of ambulances or medical insignia to transport fighters or munitions, and fighters dressing in civilian clothing to draw protected-status confidence have been raised in theatres including Iraq, Afghanistan, the Syrian civil war, and the Russo-Ukrainian war since 2022, where both Kyiv and Moscow have traded accusations of feigned surrender.

Perfidy must be carefully distinguished from the ruse of war, which Article 37(2) of AP I expressly permits. Ruses are acts intended to mislead an adversary or induce reckless conduct but which infringe no rule of international law and do not invite confidence in legal protection — examples include camouflage, decoys, mock operations, and misinformation. Wearing the enemy's uniform behind one's own lines or to deceive may be a lawful ruse, but using it during an attack crosses into the Article 39 prohibition. The decisive line is whether the deception exploits a legally protected status. Espionage is likewise distinct: a spy who is captured forfeits prisoner-of-war status but commits no perfidy merely by gathering information in disguise.

Edge cases and controversies persist. The status of assassination using feigned protected status — such as the targeting of an adversary by an operative posing as a medic — remains debated, and the legality of certain decapitation strikes has been analyzed through the perfidy lens. Naval warfare carries a recognized historical exception: a warship may fly false colours as a ruse but must hoist its true flag before opening fire, a customary rule reflected in the 1994 San Remo Manual. Cyber and information operations raise unsettled questions about whether digital impersonation of protected entities could constitute perfidy, a matter examined in the Tallinn Manual 2.0. The use of human shields and the blurring of combatant and civilian appearance in asymmetric conflicts continue to generate perfidy allegations that are difficult to adjudicate.

For the working practitioner, the prohibition of perfidy is more than a doctrinal nicety: it protects the very signals — the white flag, the red cross, the surrendering hand — on which battlefield restraint depends. Each act of perfidy erodes the credibility of these signals and invites adversaries to fire on the genuinely wounded or surrendering, escalating brutality. Legal advisers, targeting officers, and accountability investigators must distinguish perfidy from lawful ruses with precision, because a finding of perfidy supports individual criminal responsibility under the ICC Statute and domestic war-crimes legislation. Mastery of the Article 37 test remains essential to advising commanders and documenting violations.