Perfidy

In the context of war, perfidy is a form of deception in which one side promises to act in good faith (such as by raising a flag of truce) with the intention of breaking that promise once the enemy is exposed (such as by coming out of cover to attack the enemy coming to take the "surrendering" prisoners into custody). Perfidy constitutes a breach of the laws of war and so is a war crime, as it degrades the protections and mutual restraints developed in the interest of all parties, combatants, and civilians.

In practice, combatants find it difficult to respect protected persons and objects if experience causes them to believe or suspect that their adversaries are abusing a claim to protection under international law to gain a military advantage.

Perfidy is specifically prohibited under the 1977 , which states:

Article 37. – Prohibition of perfidy
1. It is prohibited to kill, injure or capture an adversary by resort to perfidy. 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, shall constitute perfidy. The following acts are examples of perfidy:
(a) The feigning of an intent to negotiate under a flag of truce or of a surrender;
(b) The feigning of an incapacitation by wounds or sickness;
(c) The feigning of civilian, non-combatant status; and
(d) The feigning of protected status by the use of signs, emblems or uniforms of the United Nations or of neutral or other States not Parties to the conflict.
2. Ruses of war are not prohibited. Such ruses are acts which are intended to mislead an adversary or to induce him to act recklessly but which infringe no rule of international law applicable in armed conflict and which are not perfidious because they do not invite the confidence of an adversary with respect to protection under that law. The following are examples of such ruses: the use of camouflage, decoys, mock operations and misinformation.

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Wikipedia