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United States of America
Practice Relating to Rule 117. Accounting for Missing Persons
Section D. Right of the families to know the fate of their relatives
The US Field Manual (1956) reproduces Article 26 of the 1949 Geneva Convention IV. 
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, § 265.
The US Air Force Pamphlet (1976) stipulates that the 1949 Geneva Convention IV contains “measures for facilitating the establishment of contact between members of a family who have been separated because of the war”. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 14-3.
The Annotated Supplement to the US Naval Handbook (1997) states: “The United States also supports the new principles in [the 1977 Additional Protocol] I, art. 32 & 34, that families have the right to know the fate of their relatives.” 
United States, Annotated Supplement to the Commander’s Handbook on the Law of Naval Operations, prepared by the Oceans Law and Policy Department, Center for Naval Warfare Studies, Naval War College, Newport, Rhode Island, November 1997, § 11.4, footnote 19.
At the CDDH in 1974, the United States referred to “the anguish of the families of persons of whom there was no word during conflicts” and stressed
the need to inform those families of the fate of their missing relatives as soon as possible, and pointed out that the draft followed logically from resolution V adopted on that subject by the XXIInd International Conference of the Red Cross at Teheran in 1973. 
United States, Statement at the CDDH, Official Records, Vol. XI, CDDH/II/SR.6, 14 March 1974, p. 41, § 4.
At the CDDH in 1976, the United States stated:
The statement of the right of the families to know the fate of their relatives was of primary importance for the understanding of the Section under discussion. Paragraph 1 of article 20 bis did not refer to other sections of the draft Protocol or the Geneva Conventions. If the right of the families was not specifically mentioned, the section might be interpreted as referring to the right of Governments, for instance, to know what had happened to certain missing persons … As regards [a] query of the Yugoslav representative whether paragraph 1 of article 20 bis was necessary, he agreed that it was unusual to state the premises on which an article was based. The paragraph had been included in response to a strong feeling of many delegations and institutions that it was important to express in the Protocol the idea that families had a right to know what had happened to their relatives. United Nations General Assembly resolution 3220 (XXIX), which the Working Group had studied when drawing up the present text, stated in the last preambular that “the desire to know … is a basic human need”, but the next under consideration went even further by referring to the “right”. 
United States, Statement at the CDDH, Official Records, Vol. XII, CDDH/II/SR.76, 1 June 1976, p. 232, §§ 28–29.
In 1987, the Deputy Legal Adviser of the US Department of State affirmed: “We support the principle that families have a right to know the fate of their relatives.” 
United States, Remarks of Michael J. Matheson, Deputy Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, American University Journal of International Law and Policy, Vol. 2, 1987, p. 424.