Related Rule
United States of America
Practice Relating to Rule 65. Perfidy
Section A. General
The US Field Manual (1956) states:
The line of demarcation between legitimate ruses and forbidden acts of perfidy is sometimes indistinct … It would be an improper practice to secure an advantage of the enemy by deliberate lying or misleading conduct which involves a breach of faith, or when there is a moral obligation to speak the truth …
Treacherous or perfidious conduct in war is forbidden because it destroys the basis for a restoration of peace short of the complete annihilation of one belligerent by the other. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 50.
The US Air Force Pamphlet (1976) states:
Perfidy or treachery involves acts inviting the confidence of the adversary that he is entitled to protection or is obliged to accord protection under international law, combined with intent to betray that confidence … Like ruses perfidy involves simulation, but it aims at falsely creating a situation in which the adversary, under international law, feels obliged to take action or abstain from taking action, or because of protection under international law neglects to take precautions which are otherwise necessary … In addition, perfidy tends to destroy the basis for restoration of peace and causes the conflict to degenerate into savagery. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 8-3(a).
The US Instructor’s Guide (1985) notes: “The law of war prohibits treacherous acts.” 
United States, Instructor’s Guide – The Law of War, Headquarters Department of the Army, Washington, April 1985, p. 8.
The US Naval Handbook (1995) states:
The use of unlawful deceptions is called “perfidy”. Acts of perfidy are deceptions designed to invite the confidence of the enemy to lead him to believe that he is entitled to, or is obliged to accord, protected status under the law of armed conflict, with the intent to betray that confidence. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 12.1.2.
The US Naval Handbook (2007) states:
The use of unlawful deceptions is called “perfidy”. Acts of perfidy are deceptions designed to invite the confidence of the enemy to lead him to believe that he is entitled to, or is obliged to accord, protected status under the law of armed conflict, with the intent to betray that confidence. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Homeland Security, US Coast Guard, July 2007, § 12.1.2.
In 1991, in response to an ICRC memorandum on the applicability of IHL in the Gulf region, the US Department of the Army stated that its practice was consistent with the definition and prohibition of perfidy contained in Article 37 of the 1977 Additional Protocol I. 
United States, Letter from the Department of the Army to the legal adviser of the US Army forces deployed in the Gulf region, 11 January 1991, § 8(J), Report on US Practice, 1997, Chapter 2.8.
In 1992, in its final report to Congress on the conduct of the Gulf War, the US Department of Defense stated:
Perfidy is prohibited by the law of war. Perfidy is defined in Article 37(1) of [the 1977 Additional Protocol I] 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 law [of war], with intent to betray that confidence …
Perfidious acts are prohibited on the basis that perfidy may damage mutual respect for the law of war, may lead to unnecessary escalation of the conflict, may result in the injury or death of enemy forces legitimately attempting to surrender or discharging their humanitarian duties, or may impede the restoration of peace …
However, there does not appear to have been any centrally directed Iraqi policy to carry out acts of perfidy. The fundamental principles of the law of war applied to Coalition and Iraqi forces throughout the war. 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Appendix O, The Role of the Law of War, ILM, Vol. 31, 1992, p. 632.